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National Park Service U.S. Department of the Interior Christiansted National Historic Site Christiansted, VI Fort Christiansvaern and Stable Building Historic Structure Report Volume 2 of 2 Cultural Resources Partnerships and Science Division Interior Region 2 Fort Christiansvaern and Stable Building Christiansted National Historic Site Historic Structure Report Volume 2 of 2 2023 for Christiansted National Historic Site Interior Region 2: South Atlantic-Gulf, National Park Service by JKOA JOSEPH K. OPPERMANN–ARCHITECT, P.A. 539 N. Trade Street Winston-Salem, NC 27101 www.jkoa.net | office@jkoa.net | (336)721-1711 The historic structure report presented here exists in two formats. A traditional, printed version is available for study at the park, at the Interior Region 2: South Atlantic-Gulf office of the National Park Service (NPS), and at a variety of other repositories. For more widespread access, the historic structure report also exists in digital format through the IRMA Portal, Integrated Resource Management Applications, including the NPS Data Store, accessed at <https:// irma.nps.gov/App/Reference/Welcome>, a website of the National Park Service. Cultural Resources, Partnerships, and Science Division Interior Region 2: South Atlantic-Gulf National Park Service 100 Alabama St. SW Atlanta, GA 30303 (404) 507-5847 September 2023 Historic Structure Report Fort Christiansvaern and Stable Building Christiansted National Historic Site (CHRI) CRIS Number: Fort: 00188 Stable: 091554 Cover Photo: JKOA, July 2021 Christiansted National Historic Site Historic Structures Report Fort Christiansvaern and Stable Building and Associated Stableyard, Gate and Walls Christiansted, St. Croix, U. S. Virgin Islands Approved: ________________________________________________________________ Superintendent, Christiansted National Historic Site Date Recommended: ________________________________________________________________ Chief, Cultural Resources, Partnerships, and Science Date Interior Region 2, South Atlantic Gulf Recommended: ________________________________________________________________ Deputy Regional Director Date Interior Region 2, South Atlantic Gulf Approved: ________________________________________________________________ Regional Director, Interior Region 2, South Atlantic Gulf Date Regional Director, Interior Region 2, National Park Service Date ANGELITA ALVINO Digitally signed by ANGELITA ALVINO Date: 2023.10.12 09:54:36 -04'00' JULIE ERNSTEIN Digitally signed by JULIE ERNSTEIN Date: 2024.03.28 08:21:36 -04'00' KAREN CUCURULLO Digitally signed by KAREN CUCURULLO Date: 2024.09.17 13:54:48 -04'00' MARK FOUST Digitally signed by MARK FOUST Date: 2024.09.19 08:23:56 -04'00' Foreword We are pleased to make available this Historic Structures Report for Fort Christiansvaern and its associated Stable Building at Christiansted National Historic Site, part of the ongoing effort to provide comprehensive documentation for the historic structures of the National Park Service. The success of this project is due in large part to the staff of the Christiansted National Historic Site. The park has long sought to protect and interpret this important resource. Evan Gwilliam, the Park’s Supervisory Resource Management Specialist, as well as staff from the park and the region have assisted in providing support for this project. We would like to thank Project Lead Joseph K. Oppermann, FAIA, Preservation Architect Robert J. Hotes, Architectural Historian Langdon E. Oppermann, Architectural Staff Christopher Woolard and Jeffrey P. Anderson, of Joseph K. Oppermann - Architect, P.A., Structural Engineer John Matteo of MCC 1200 Architectural Engineers, PLLC, and Architectural Conservator Dorothy Krotzer of Building Conservation Associates for their thorough research, rigorous existing conditions documentation, and carefully considered recommendations. The Park would also like to thank Interior Region 2 for their careful reviews and contributions on this project. Angelita Alvino Superintendent 8 HSR, Fort Christiansvaern and Stable Building Table of Contents Volume 1 Foreword Project Team....................................................................................................................................iii List of Figures................................................................................................................................... v Management Summary........................................................................................ xxxi Part I - Developmental History Historical Background and Context.......................................................................... 1 Chronology of Development and Use...................................................................... 21 Section I – Herbert Olsen, Historic Structure Report, Fort Christiansvaern, 1960................21 Section II – The Fort, 1960 to the present................................................................................101 Section III – The Stableyard Complex, 1960 to the present...................................................131 Bibliography...........................................................................................................141 Physical Description and Condition Assessment....................................................145 Physical Description General Description............................................................................................................................... 145 Exterior Organization............................................................................................................................ 147 Exterior Features.................................................................................................................................... 162 Room-by-Room Description................................................................................................................ 201 Character-Defining Features......................................................................................................313 Condition Assessment................................................................................................................315 Significance & Integrity..........................................................................................327 Part II - Treatment and Use Requirements for Treatment and Use........................................................................................331 Ultimate Treatment and Use.......................................................................................................337 Alternatives for Treatment and Use..................................................................................................... 337 Recommendations for Achieving Ultimate Treatment and Use.............................................341 Guidelines for Treatment and Use....................................................................................................... 341 Exterior Features.................................................................................................................................... 343 Interior Features..................................................................................................................................... 357 Ventilation and Building Systems......................................................................................................... 363 Structural System................................................................................................................................... 366 Accessibility and Universal Design...................................................................................................... 375 Resilience to Natural Hazards.............................................................................................................. 376 Recommendations for Ultimate Use................................................................................................... 378 Recommendations for Further Research............................................................................................ 380 National Park Service i Monitoring Checklist...................................................................................................................385 Implementation Projects..............................................................................................................387 Volume 2 Appendix A 1959 Historic American Buildings Survey (HABS) Documentation Drawings Appendix B Historical Epoch Drawings Appendix C Annotated HABS Documentation Drawings Showing Present Conditions Appendix D Selected Utility Drawings Appendix E Structural Investigation Report by 1200AE Appendix F Materials Analyses Report by BCA ii HSR, Fort Christiansvaern and Stable Building Project Team Joseph K. Oppermann–Architect, P.A. (JKOA) Joseph K. Oppermann, FAIA, APT RP, Historical Architect and Principal-in-Charge Robert J. Hotes, AIA, NCARB, APT RP, LEED AP BD+C, Historical Architect Jeffrey P. Anderson, Assoc. AIA Langdon E. Oppermann, Architectural Historian/Planner Christopher M. Woollard, Assoc. AIA In Collaboration with: MCC≡1200 Architectural Engineers PLLC (1200AE) John A. Matteo, PE, FAAR, Principal Nicole Ferran, PE, Senior Engineer II Building Conservation Associates Inc. (BCA) Dorothy S. Krotzer, Director Prepared for: National Park Service – Interior Region 2: South Atlantic-Gulf Celinda Hicks, Contracting Officer Megan Jenkins, AIA, NCARB, Contracting Officer’s Technical Representative National Park Service – Christiansted National Historic Site Angelita Alvino, Park Superintendent Evan Gwilliam, Supervisory Resource Management Specialist National Park Service iii iv HSR, Fort Christiansvaern and Stable Building Appendix A: 1959 HABS Documentation Drawings 1959 HABS Documentation Sheet 1 of 26 1959 HABS Documentation Sheet 2 of 26 1959 HABS Documentation Sheet 3 of 26 1959 HABS Documentation Sheet 4 of 26 1959 HABS Documentation Sheet 5 of 26 1959 HABS Documentation Sheet 6 of 26 1959 HABS Documentation Sheet 7 of 26 1959 HABS Documentation Sheet 8 of 26 1959 HABS Documentation Sheet 9 of 26 1959 HABS Documentation Sheet 10 of 26 1959 HABS Documentation Sheet 11 of 26 1959 HABS Documentation Sheet 12 of 26 1959 HABS Documentation Sheet 13 of 26 1959 HABS Documentation Sheet 14 of 26 1959 HABS Documentation Sheet 15 of 26 1959 HABS Documentation Sheet 16 of 26 1959 HABS Documentation Sheet 17 of 26 1959 HABS Documentation Sheet 18 of 26 1959 HABS Documentation Sheet 19 of 26 1959 HABS Documentation Sheet 20 of 26 1959 HABS Documentation Sheet 21 of 26 1959 HABS Documentation Sheet 22 of 26 1959 HABS Documentation Sheet 23 of 26 1959 HABS Documentation Sheet 24 of 26 1959 HABS Documentation Sheet 25 of 26 1959 HABS Documentation Sheet 26 of 26 Appendix B: Historical Epochs Drawings This appendix includes historic plans of the fort for five identified epochs, including: 1780, 1836, 1919, 1953, and 1959. Each plan after 1780 is followed by an annotated version calling out changes since the previous epoch. Changes since 1959 are included in Appendix C. Sheet 1: 1778-1780 First-floor plan by Peter Lotharius Oxholm Sheet 2: 1778-1780 Second-floor plan by Peter Lotharius Oxholm Sheet 3: 1836 First-floor plan by First Lieutenant Gjellurup and Second Lieutenant Friis. Sheet 4: 1836 First-floor plan with changes annotated Sheet 5: 1836 Second-floor plan by First Lieutenant Gjellurup and Second Lieutenant Friis Sheet 6: 1836 Second-floor plan with changes annotated Sheet 7: 1836 Roof plan by First Lieutenant Gjellurup and Second Lieutenant Friis Sheet 8: 1836 Roof plan with changes annotated Sheet 9: 1919 First-floor plan by Tyge Hvass Sheet 10: 1919 First-floor plan with changes annotated Sheet 11: 1919 Second-floor plan by Tyge Hvass Sheet 12: 1919 Second-floor plan with changes annotated Sheet 13: 1953 First-floor plan by Frederick Gjessing Sheet 14: 1953 First-floor plan with changes annotated Sheet 15: 1953 Second-floor plan by Frederick Gjessing Sheet 16: 1953 Second-floor plan with changes annotated Sheet 17: 1959 First-floor plan, Historic American Buildings Survey (HABS) (No substantive changes since 1953) Sheet 18: 1959 Second-floor plan, HABS (No substantive changes since 1953) Historical Epoch Drawings 1 of 18 1778-1780 First-floor Plan Historical Epoch Drawings 2 of 18 1778-1780 Second-floor Plan Historical Epoch Drawings 3 of 18 1836 First-floor Plan Historical Epoch Drawings 4 of 18 1836 First-floor Plan (Annotated) SHED ROOF SHED ROOF ADDED ADDED AT EAST AT EAST CURTAIN CURTAIN PARTITIONS PARTITIONS REMOVED REMOVED AND WINDOWS AND WINDOWS ENLARGED ENLARGED CARRIAGE CARRIAGE HOUSE HOUSE CONSTRUCTED CONSTRUCTED LAUNDRY HOUSE LAUNDRY HOUSE CONSTRUCTED CONSTRUCTED STABLE STABLE AND ASSOCIATED AND ASSOCIATED SITE WALLS & SITE WALLS & GATE GATE CONSTRUCTED CONSTRUCTED WINDOW WINDOW AND AND DOOR DOOR REVERSED REVERSED ARTILLERY ARTILLERY SHED SHED CONSTRUCTED CONSTRUCTED WINDOW WINDOW ADDED ADDED STAIR STAIR MODIFIED MODIFIED STAIR TO STAIR TO UPPER LEVEL UPPER LEVEL ADDED ADDED DOORWAYS DOORWAYS AT PREVIOUS AT PREVIOUS WINDOWS WINDOWS OPENING OPENING IN PARTITION IN PARTITION CLOSED CLOSED PARITITION PARITITION ADDED ADDED DOORWAY DOORWAY AT PREVIOUS AT PREVIOUS WINDOW WINDOW PRISON YARD PRISON YARD WALL WALL CONSTRUCTED CONSTRUCTED LATRINES LATRINES EXPANDED EXPANDED STOVE STOVE REMOVED REMOVED Historical Epoch Drawings 5 of 18 1836 Second-floor Plan Historical Epoch Drawings 6 of 18 1836 Second-floor Plan (annotated) NORTHEAST NORTHEAST BASTION SECOND BASTION SECOND LEVEL AND ROOF LEVEL AND ROOF CONSTRUCTED CONSTRUCTED CARRIAGE CARRIAGE HOUSE HOUSE CONSTRUCTED CONSTRUCTED LAUNDRY HOUSE LAUNDRY HOUSE CONSTRUCTED CONSTRUCTED STABLE STABLE AND ASSOCIATED AND ASSOCIATED SITE WALLS & SITE WALLS & GATE GATE CONSTRUCTED CONSTRUCTED PARTITIONS PARTITIONS REMOVED REMOVED STAIR TO LOWER LEVEL ADDED PARTITION ADDED PRISON YARD WALL CONSTRUCTED LATRINES EXTENDED SHED ROOF SHED ROOF ADDED ADDED AT EAST AT EAST CURTAIN CURTAIN SHED ROOF SHED ROOF ADDED ADDED AT SOUTH AT SOUTH CURTAIN CURTAIN SHED ROOF SHED ROOF ADDED ADDED AT EAST AT EAST CURTAIN CURTAIN Historical Epoch Drawings 7 of 18 1836 Roof Plan Historical Epoch Drawings 8 of 18 1836 Roof Plan (annotated) NORTHEAST NORTHEAST BASTION SECOND BASTION SECOND LEVEL AND ROOF LEVEL AND ROOF CONSTRUCTED CONSTRUCTED CARRIAGE CARRIAGE HOUSE HOUSE CONSTRUCTED CONSTRUCTED STAIR TO STAIR TO LOWER LOWER LEVEL ADDED LEVEL ADDED PRISON YARD PRISON YARD WALL WALL CONSTRUCTED CONSTRUCTED LATRINES LATRINES EXTENDED EXTENDED ARTILLERY ARTILLERY SHED ADDED SHED ADDED SHED ROOF SHED ROOF ADDED ADDED AT EAST AT EAST CURTAIN CURTAIN SHED ROOF SHED ROOF ADDED ADDED AT SOUTH AT SOUTH CURTAIN CURTAIN LAUNDRY HOUSE LAUNDRY HOUSE CONSTRUCTED CONSTRUCTED STABLE STABLE AND ASSOCIATED AND ASSOCIATED SITE WALLS & SITE WALLS & GATE GATE CONSTRUCTED CONSTRUCTED Historical Epoch Drawings 9 of 18 1919 First-floor Plan Historical Epoch Drawings 10 of 18 1919 First-floor Plan (annotated) STAIR TO UPPER LEVEL ELIMINATED NORTHEAST BASTION WINDOW OPENINGS RECONFIGURED NORTHWEST BASTION WINDOW OPENINGS RECONFIGURED STAIR TO STABLEYARD ADDED ARTILLERY SHED NOT SHOWN WINDOW OPENINGS ADDED/ RECONFIGURED EXTERIOR STAIR TO UPPER LEVEL ADDED RETAINING WALL AND EXTERIOR STAIR ADDED Historical Epoch Drawings 11 of 18 1919 Second-floor Plan Historical Epoch Drawings 12 of 18 1919 Second-floor Plan (annotated) STAIR TO LOWER LEVEL ELIMINATED Historical Epoch Drawings 13 of 18 1953 First-floor Plan Historical Epoch Drawings 14 of 18 1953 First-floor Plan (annotated) PLANTER ADDED GARAGE CONSTRUCTED DOORWAYS IN PARITION WALLS RECONFIGURED BATHROOM PARITIONS ADDED; WINDOW OPENINGS RECONFIGURED NORTHEAST BASTION WINDOW OPENINGS RECONFIGURED Historical Epoch Drawings 15 of 18 1953 Second-floor Plan Historical Epoch Drawings 16 of 18 1953 Second-floor Plan (annotated) PARITION RECONFIGURED DOORWAY WIDENED Historical Epoch Drawings 17 of 18 1959 First-floor Plan (No substantive changes since 1953) Historical Epoch Drawings 18 of 18 1959 Second-floor Plan (No substantive changes since 1953) Appendix C: Annotated HABS Documentation Drawings Showing Present Conditions Sheet 1: Context Plan Sheet 2: First-floor Plan (South) Sheet 3: First-floor Plan (North) Sheet 4: Stableyard Plan Sheet 5: Second-floor Plan (South) Sheet 6: Second-floor Plan (North) Sheet 7: Southwest, West, and East Elevations Sheet 8: Sections - Ravelin, South Curtain, and Water Battery Sheet 9: Sections - South and East Curtains Sheet 10: Section-Elevations - South Curtain Sheet 11: Section-Elevations - Stableyard and Courtyard 1/32” =1’-0” 1 CONTEXT PLAN SCALE: 1/32” = 1’-0” DEMOLISHED STAIR RUINS HIP ROOF REMOVED WATER BATTERY COURTYARD WEST CURTAIN EAST CURTAIN LATRINES NORTHWEST BASTION NORTHEAST BASTION SOUTHWEST BASTION SOUTHEAST BASTION RAVELIN YARD STABLEYARD STABLE PRISON YARD CARRIAGE HOUSE PLAN NORTH FIRST-FLOOR PLAN (SOUTH) SCALE: 1/16” = 1’-0” 1/16” =1’-0” 2 PLANTER REMOVED AND PAVED PARTITION ADDED PARTITION AROUND CISTERN REMOVED BAR PARTITIONS ADDED WINDOW OPENING INFILLED AT INTERIOR 5 6 7 8 9 10 11 12 13 14/15 16 17 26A 26B 26C 26D 27 28 33 PLAN NORTH FIRST-FLOOR PLAN (NORTH) SCALE: 1/16” = 1’-0” 1/16” =1’-0” 3 BAR PARTITIONS ADDED BAR PARTITIONS ADDED TILE FLOOR, PLUMBING FIXTURES & STALLS ADDED LATER PARTITION REMOVED 18 19 20 21 22/23 24A 24B 24C 25 26E 1 2 3 4 PLAN NORTH STABLEYARD PLAN SCALE: 1/16” = 1’-0” 1/16” =1’-0” 4 DEMOLISHED RUINS WOOD GATE WOOD GATE WOOD SCREEN PARTITIONS (TYP.) RAISED PLYWOOD FLOOR ADDED TO ROOM 31A 29 30 31A 31B PLAN NORTH SECOND-FLOOR PLAN (SOUTH) SCALE: 1/16” = 1’-0” 1/16” =1’-0” 5 PARTITION REMOVED G H I/K L M PLAN NORTH SECOND-FLOOR PLAN (NORTH) SCALE: 1/16” = 1’-0” 1/16” =1’-0” 6 N PLAN NORTH SOUTHWEST, WEST, AND EAST ELEVATIONS SCALE: 1/32” = 1’-0” 1/32” =1’-0” 7 WINDOW SASH REMOVED AT SECOND FLOOR HIP ROOF REMOVED HIP ROOF REMOVED HIP ROOF REMOVED SECTIONS - RAVELIN, SOUTH CURTAIN, AND WATER BATTERY SCALE: 1/16” = 1’-0” 1/16” =1’-0” 8 DOORS REMOVED AT GALLERY HIP ROOF REMOVED SECTIONS - SOUTH AND EAST CURTAINS SCALE: 1/16” = 1’-0” 1/16” =1’-0” 9 WINDOW SASH REMOVED AT SECOND FLOOR (TYP.) TRAY CEILING REMOVED IN ROOM G FLAGPOLE REMOVED AT SOUTHWEST BASTION HIP ROOF REMOVED HIP ROOF REMOVED SECTION-ELEVATIONS - SOUTH CURTAIN SCALE: 1/16” = 1’-0” 1/16” =1’-0” 10 HIP ROOF REMOVED HIP ROOF REMOVED WINDOW SASH REMOVED AT SECOND FLOOR (TYP.) SHUTTERS, WINDOW SASH, AND DOORS REMOVED AT GALLERY (TYP.) SECTION-ELEVATIONS - COURTYARD AND STABLEYARD SCALE: 1/16” = 1’-0” 1/16” =1’-0” 11 FLAGPOLE INSTALLED AT NORTHWEST BASTION STALL PARTITIONS REMOVED IN STABLE WOOD SCREENS INSTALLED IN ARCHES PAIRED DOORS INSTALLED Appendix D: Selected Utility Drawings Sheet 1: Electrical Plan, 2010 Sheet 2: Ground Floor HVAC Drain Layout Plan, 2010 Sheet 3: Ground Floor HVAC Layout Plan Details, 2010 Sheet 4: Fire Alarm Networking Detail of Buildings, 2016 Sheet 5: First-floor Fire Alarm System Plan, 2016 Sheet 6: Second-floor Fire Alarm System Plan, 2016 Sheet 7: Stable Fire Alarm Plan, 2016 Sheet 8: Fire Alarm Riser Diagram, 2016 Sheet 9: Fire Alarm System Calculations, 2016 Sheet 10: Fire Alarm Details and Specifications, 2016 2010 HVAC/Electrical Plans Sheet 1 of 3 2010 HVAC/Electrical Plans Sheet 2 of 3 2010 HVAC/Electrical Plans Sheet 3 of 3 2016 Fire Alarm Plans Sheet 1 of 7 2016 Fire Alarm Plans Sheet 2 of 7 2016 Fire Alarm Plans Sheet 3 of 7 2016 Fire Alarm Plans Sheet 4 of 7 2016 Fire Alarm Plans Sheet 5 of 7 2016 Fire Alarm Plans Sheet 6 of 7 2016 Fire Alarm Plans Sheet 7 of 7 Appendix E: Structural Investigation Report by 1200AE Fort Christiansvaern and Stable Building Historic Structure Report 1200AE PROJECT NO. 20-131 July 19, 2023 Prepared For: Joseph K. Oppermann - Architect, P. A. 539 N. Trade St. Winston-Salem, NC 27101 By: 1200 Architectural Engineers, PLLC 210 North Lee Street, Suite 210 Alexandria, VA 22314 T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Introduction 1200 Architectural Engineers (1200AE) was contracted to assist with preparing a Historic Structures Report (HSR) for Fort Christiansvaern in Christiansted, St. Croix, U.S. Virgin Islands. The scope of the HSR includes Fort Christiansvaern (1738) and its Stable Building (1836) and the associated Stableyard, Gate, and Walls. This HSR is intended to update a previous HSR produced in 1960, including a review of research and documentation of historic treatment and restoration efforts undertaken since that time. In addition, it will provide recommendations for future maintenance, preservation, and use of the structures. (Google Maps). Figure 1: Aerial View of Fort Christiansvaern Fort Christiansvaern is located on the shoreline of Christiansted Harbor and is sited on the earthworks of the earlier French fortification. Construction of the fort was begun in 1738 during the Danish occupation and largely completed by 1749, with the last major additions dating from 1835-1841. After 1878, the fort was used as a police station and courthouse. In 1952, the U.S. Secretary of the Interior, through a Memorandum of Agreement with the Governor of the Virgin Islands, established Virgin Islands National Historic Site, which in 1960 was renamed Christiansted National Historic Site. The structure measures approximately 132 feet by 144 feet and is built around a central rectangular courtyard. It has vaulted masonry corner bastions built at salient angles and a ravelin on the landward (south) side to protect the two-story south curtain and sally port. The south curtain houses a second-floor gallery which overlooks the central courtyard. The bastions are connected on the east and west elevations by one-story curtains which support terrepleins and on the north side by a water battery. A stableyard, carriage house and stables are located to the east of the fort at a lower elevation. The fort structure consists of brick and rubble masonry load-bearing walls. Framed floors and roofs are built with one of three systems depending on location: brick vaults support the bastion floor and roof structure and the water battery, timber framing with wood planks support the south curtain second floor, and timber framing supports the flat or low-slope brick roofs. In isolated locations within the west curtain, earlier timber construction was replaced with reinforced concrete structure. The yellow brick used T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report throughout the fort is said to have been brought from Denmark in sailing vessels as ballast. As part of the current efforts, 1200AE conducted a detailed site investigation of the Fort on May 28 through May 30, 2021, documenting via field notes and photographs the existing conditions of the structures and localized structural geometry, including typical framing member dimensions and floor and roof system assemblies and dimensions. A follow up site visit was performed on February 14 through February 15, 2022, to perform a more detailed assessment of the deteriorated timber girder at the Commandant’s Gallery. These field observations along with a review of various existing drawings and documents are used as the basis for a preliminary structural analysis of isolated structural elements to evaluate historic and current load patterns on the structure, including areas of potential structural concern noted by 1200AE on site. This review is then followed by a discussion of the analysis results and prioritized recommendations for future structural preservation work. Review of Existing Documents The following existing drawings and documents were provided by the National Park Service and are referenced for this report: Drawings: 1. “Main floor plan and stable yard plan,” April 1953 (NHS-VI-250). 2. “Plan of second floor & gun decks,” April 1953 (NHS-VI-251). 3. “Sections thru flat brick roofs,” April 1953 (NHS-VI-252). 4. Historic American Building Survey, December 1959, Sheets 1-26. Reports and other documents: 5. Condition Report of Historic Buildings, Virgin Islands National Historic Site, Christiansted, St. Croix, Virgin Islands: Christiansvaern Fort by Frederik C. Gjessing, Architect, May 1956. 6. Historic Structure Report (HSRs) for Fort Christiansvaern (H-3, LCS 188) and Stable Building (H-9, LCS 91554), located within Christiansted National Historic Site St. Croix, U. S. Virgin Islands, Herbert Olsen, 1960. 7. General Management Plan / Environmental Assessment, Christiansted National Historic Site, National Park Service, June 1986. 8. Historic Structure Treatment Record, Emergency Stabilization of the Christiansted NHS Gallery Floor by the Historic Preservation Training Center, February 2015. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Past Structural Investigations and Preservation Efforts Based on information provided to 1200AE and noted above, past structural investigations or structural preservation efforts conducted at Fort Christiansvaern are extensive. Those which have been completed are primarily in response to noted areas of deterioration and past extreme weather events. Known past investigations and recommendations relating to the existing structure as well as previous repair campaigns are discussed in more detail in the architectural section of this report but include the following: 1. 1956 Condition Report of Historic Buildings: This report was written after the fort became part of the Virgin Islands National Historic Site in 1952. The following observations and recommendations were made as part of this report: • Replace the second-floor roofs. • The 1st floor roofs supporting the gun decks were noted to be in poor condition, especially in the southwest and southeast bastions. • At the southwest bastion and adjoining rooms, the beam supports had rotted out and required replacement. • At the ravelin immediately east of the sally port, the vault and roof needed restoration. A similar condition existed at the roof of the stables. • The brick paving had extensive vegetation growing in it and required restoration. • At the south curtain second story porch, the parapet wall was noted to be cracked. 2. Major repair/restoration work is understood to have been undertaken by the NPS in the early 1980s, including reconstruction of both terreplein (gun decks). Extensive masonry repairs consisted of pointing in areas of mortar deterioration, grouting of cracks, and replacement of bricks and stones to match existing construction where needed. Replacement and repair of wood framing elements was also documented, including a preservation treatment of the wood. 3. Post-hurricane repairs are understood to have taken place and are described in more detail in the architectural section of this report. Hurricane Hugo (Category 4; September 17, 1989) inflicted significant damage to the fort and caused it to be closed temporarily. Post-hurricane repairs included reconstruction of the latrine roof, which had had been torn off; replacement of the flagpole in the Northwest bastion; and repair or replacement of numerous doors and windows. The west and east site wingwalls were partially destroyed by impact from large yachts thrown by the storm and were later reconstructed. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Later hurricanes include Hurricanes Marilyn (Strong Category 2; September 15,1995), Omar (Category 3; October 15, 2008), and Irma / Maria (Category 5; September 6 and 20, 2017). Following Hurricane Marilyn, repairs included localized roof repairs and repairs to windows, doors, and shutters. Hurricane Omar caused more significant damage and required more extensive repairs, including repairs to severe cracking in the fort’s masonry walls, replacement of roofs and repair of the flagpole at the northwest bastion. 4. 2015 Historic Structure Treatment Record by HPTC: • The Historic Structure Treatment Record (HSTR) is a statement of the Emergency Stabilization of the Christiansted NHS Gallery Floor completed by personnel of the National Park Service, Historic Preservation Training Center (HPTC) from January 19th through February 26th, 2015. The Final Project Agreement, dated November 2014, included as an appendix in the HSTR, indicated two primary areas of work: the second floor Gallery and the exhibit area in the south curtain and southwest bastion. This document appears to have been revised in December 2014 to eliminate the scope for the exhibit areas and therefore it is assumed that this work has not been completed. Second Floor Gallery • The floor area located on the second floor Gallery of the fort, located between the two staircases over the breezeway was noted to be sagging. The timber beams and wooden boards supporting the floor were damaged by long term moisture exposure and termite activity. In the two most seriously deteriorated areas, the cribbing was sagging and ready to fall. Temporary shoring was installed to stabilize the ceiling until a repair could be devised. • The floor construction was dismantled to facilitate replacement and repair of deteriorated members. Floor composition was noted to consist of masonry tile set on 6” fill supported by modern 3/4”x5-1/4” tongue and groove wood planking on 6”x7” timber beams spaced at 34” on center. The historic planking found in the gallery hallways was measured to be 1-1/2” thick and random width. The 3/4" tongue and groove boards were noted to have been installed as part of repair work performed in the 1980s and 1990s. • As part of the repair work, the 3/4" tongue and groove boards were replaced with 1-1/2” thick random width mahogany to match the historic configuration. Deteriorated beams were replaced with mahogany beams to match the existing. Approximately 70% of the planking and beams were noted to have been replaced. Pressure treated plywood (3/4”) was installed above the boards and a T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report waterproofing membrane (Grace Bituthene System 4000) installed over top of the plywood. The existing fill was replaced with crushed stone dust and then the salvaged tiles were reinstalled using a traditional lime-based mortar. Two coats of a waterproofing substance (WaterBan) were applied to the entire gallery floor and the joints between the pavers were filled with an impermeable grout. Exhibit Areas, South Curtain and Southwest Bastion • In the exhibit areas of the slave quarters, soldiers’ barracks and brick kitchen & oven located in the south curtain and southwest bastion at the parade ground level, the walls were noted to contain embedded iron components that were rusting and causing displacement of structural elements. The anticipated scope of work in these areas, which appears not to have been executed, was summarized in the November 2014 Final Project Agreement and is noted in more detail below. • Soldiers’ barracks: This is a trapezoidal room with four embrasure openings, each containing six iron bars 1-1/4” square which are embedded in a wooden header beam and into a masonry sill. The rusting bars caused spalling and deterioration of the masonry sills. Proposed scope of work consisted of removal of rusting iron bars, replacement of bars with non-ferrous components, reconstruction of masonry sills, repairs of wood headers, and stucco repairs to sills and groin vaults. • Slave quarters: Two openings to the courtyard had extensive damage to the wooden header and masonry sill as well as the stucco due to rust jacking. Reconstruction was recommended, although the exact tasks were not identified. • Brick Kitchen and Oven: Two openings in the oven were framed with steel / iron frames, both of which were corroding and causing damage to the surrounding masonry. The main oven chamber was noted to have partially collapsed. Careful dismantling and reconstruction were recommended. 5. Successive campaigns of termite damage assessments and treatments were performed throughout the decades. These included a report on termite activity prepared by the park biological technician in October 1987, termite monitoring and baiting in 1991, removal of tree roots in the Ravelin Yard in 1992 to help mitigate subterranean termite infestations, among other reasons, and a 1995 prototype termite treatment developed by University of Florida entomologists. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Existing Structural Systems and History of Structural Modifications As observed on site and through historic documentation, the existing structure of Fort Christiansvaern consists of a combination of masonry and timber construction. Structural systems are described below, starting at the Ravelin Yard, continuing with the south curtain, moving counterclockwise from that location around the interior courtyard, and finishing with the Stableyard and Site Structures. For room numbers and names, refer to Drawings 1 through 6 in Appendix C. Structural framing plans and select sections and details are provided in Drawings E-1 through E-11 in Appendix E.1. Ravelin Yard The Ravelin Yard was built as part of the original construction between 1738 and 1749 and is located at the southern end of the fort and is triangular in shape (Fig. 2). The west side of the triangle is defined by a masonry site wall. The east side is defined by the Ravelin (Rm. 27) with the Guard House at the southern tip (Rm. 28). The Ravelin is constructed of exterior masonry walls supporting a shed roof that slopes down towards the Ravelin Yard (Fig. 3). The wall facing the East is thicker, approximately 2’-4” thick based on the HABS drawings, and the wall facing the Ravelin Yard is thinner. Wood rafters 3” wide by 5-1/2” deep are spaced at 3’- 10” (+/-) on center and support wood roof boards and a corrugated metal roof (Fig. 4). The rafters are notched over wood sill plate over top the exterior masonry walls. Some temporary shoring of the roof is in place in the rear storage area, which is depicted and discussed in the conditions and treatment recommendations section below. The Guard House has significantly thicker masonry walls, approximately 4’-0” thick at their thinnest points (Fig. 5). The roof is framed with roof joists measured to be 4” Figure 2: Ravelin Yard as Seen from SE Bastion. Figure 3: Looking East at Ravelin West Façade. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report wide by 7-1/2” deep spaced at 18” on center (Fig. 6). Per the 1960 HSR, in 1826 the vaulted roof on the former magazine at the salient angle of the ravelin was replaced with a wood-framed roof and flat brick roofing since the vaults were severely cracked. Figure 4: Looking North within Ravelin Interior (27). Figure 5: Guard House Façade at Yard. Figure 6: Guard House Roof Framing (28). T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report South Curtain Current Existing Construction The south curtain stands at the transition from the Ravelin to the Interior Courtyard. The south façade presents the central arched entrance with a series of rectangular window openings on two levels (Fig. 7). The stucco-covered wall is constructed of brick masonry and is approximately 2’-2” thick. The north façade presents three distinct switchback stairways from the first to second floor levels, jutting out in plan into the Interior Courtyard (Fig. 8). The stair construction consists of brick masonry walls and lower-level vaulting, stuccoed on the vertical surfaces. The second level presents a continuous arcade along the full length of the façade. The typical piers are approximately 18” to 20” in width, while the piers at the east and west ends are wider, measuring approximately 2’4” in width. The increased width reflects the need for thrust resistance at the ends of the arcade. The center hall at the lower level is spanned in the southern portion by a series of groin vaults (Fig. 9). The traditional masonry vaulted form takes advantage of masonry’s strength in compression and its geometry directs these forces to discrete locations along the supporting walls. This allows for the creation of openings in the masonry walls in lesser loaded areas. The northern portion of the center hall is spanned with wood framing. Figure 7: South Curtain South Facade at Ravelin Yard. Figure 8: South Curtain North Façade at Interior Courtyard. Figure 9: South Curtain Entrance Corridor. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report At the lower level, in Room 26, some deterioration of finishes helps to expose the structural systems within (Fig. 10). The floor consists of wood boards on wood sleepers, laid directly onto the ground surface. The brick masonry walls show remnants of arches on both the south and west walls, indicating a likely change in wall openings at some point in its history. The masonry openings are typically spanned with wood lintels. The framing above at the second-floor level consists of two primary wood beams spanning north-south and dividing the space in thirds east-west. The beams are approximately 7” wide by 8” deep. Floorboards span east to west between the beams. The main east-west corridor at the lower level is sided by an approximately 2-foot 1/2” thick and random width. The 3/4" tongue and groove boards were noted to have been installed as part of repair work performed in the 1980s and 1990s. Figure 10: South Curtain Room below Stair (26). Figure 11: South Curtain Corridor below Gallery. Figure 12: South Curtain Room below Stair (26). thick wall to the south that defines the rooms of the south curtain, and a series of piers and arched openings to the north providing access to the Interior Courtyard and the vaulted spaces below the stairs (Fig. 11). The Gallery floor above is supported with wood joists spanning north-south, with sizes varying from 5 ½” square to 6” x 7” and spaced from 2’-6” to 3’-0” on center. Wood boards span east-west between the joists. Per the 2015 Historic Structure Treatment Record by HPTC, much of this floor was rebuilt by HPTC in 2015. The floor construction was dismantled to facilitate replacement and repair of deteriorated members. Floor composition was noted to consist of masonry tile set on 6” fill supported by modern 3/4”x5-1/4” tongue and groove wood planking on the timber beams. The historic planking found in the gallery hallways was measured to be 1 - - T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report As part of the 2015 repair work, the 3/4" tongue and groove boards were replaced with 1-1/2” thick random width mahogany to match the historic configuration. Deteriorated beams were replaced with mahogany beams to match the existing. Approximately 70% of the planking and beams were noted to have been replaced. Pressure treated plywood (3/4”) was installed above the boards and a waterproofing membrane installed over top of the plywood. The existing fill was replaced with crushed stone dust and then a combination of salvaged and new tiles was reinstalled using a traditional lime-based mortar. A waterproofing substance was applied to the entire gallery floor and the joints between the pavers were filled with an impermeable grout. The spaces below the stairs are generally spanned with barrel vaults (Fig. 12). The semicircular geometry of the coursed brick ceiling delivers the weight of the heavy masonry fill materials and floor above to the robust masonry side walls as a uniform load. Small arched openings offer some light to these confined spaces. At the second-floor level the robust masonry walls define a series of rooms on the south side (the Commandant’s Quarters) and the arcaded Gallery to the north. Masonry wall openings are spanned with either wood lintels or shallow masonry arches, covered with exterior stucco and interior plaster (Fig. 13). The roof framing consists of 3-1/2” x 11” wood joists spaced at 16” on center, which in turn support regularly spaced wood sleepers and the flat brick roofing system (Fig. 14). The North Gallery is sided by the masonry walls of the Commandant’s Quarters to the south and the exterior brick masonry arcade to the north. The arched Figure 13: South Curtain Second Floor (G). Figure 14: South Curtain Roof Framing. Figure 15: South Curtain North Gallery. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report openings are currently open for the most part with remnants of wood window jambs and their iron anchorages around the perimeter (Fig. 15). The roof above is spanned from north to south with 3 ¾” x 10 ¼” wood joists spaced at 17” on center typically within the narrow halls east and west. Wood sleepers and the flat brick roofing system again bear atop the joists. The center landing at the North Gallery is spanned with 4” x 10” joists over a 14” wide by 12” to 16” deep tapered girder, set below the joists which run continuously overtop north to south. Again, the same wood sleeper and brick roofing system are over top. As depicted in Fig. 16, the low girder is heavily deteriorated and has been the subject of more detailed evaluation, included as an appendix to this report. At the east side of the south curtain a wood-framed shed roof provides a sheltered transition to the North Gallery (Fig. 17). The framing is depicted on drawing 1/E-7. The light wood framing consists of 3” x 3-3/8” rafters spaced at 2’- 11” on center, supported by a 3-3/8” x 4- 7/8” primary wood member spanning over the east line of wood posts. The posts are 3-1/4” square with chamfered edges (Fig. 18). A single scarf joint is located approximately 2 feet north of the southernmost bay, and in this case seems likely part of the original construction and a means of lapping the edge framing for two shorter members rather than finding a single, slender member that would be more than 25 feet long (Figure19). The joint appears pegged with 3/4” diameter dowels. See detail 3/E-8. At the corners, the framing members are lapped overtop the posts (Fig. 20). The Figure 16: South Curtain North Gallery. Figure 17: South Curtain Shed, Looking South. Figure 18: South Curtain Shed, Underside of Roof Framing. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report full nature of the connections is somewhat hidden; however, it consists of a combination of metal fasteners and traditional timber-frame joinery. Lapping side plates with nail and screw fasteners provide the current level of tie-down of the roof framing to the posts. The anchorage of the side panels to the masonry wall of the south curtain may represent the primary tie-down, as the full nature of the connections of the posts to the roof deck below is unclear. Figure 19: South Curtain Shed, Scarf Joist in Edge History of Structural Modifications / Beam. Repairs Per the 1960 HSR, the original flat brick roof of the southern portion of the south curtain was replaced with a mansard roof between 1755 and 1767. This roof was damaged and largely blew off during a hurricane on August 31 – September 1, 1772. After the hurricane, between 1774 and 1777, a flat brick roof was constructed in place of the mansard roof again. Figure 20: South Curtain Shed, Corner Half-lapped In 1839 a new masonry stair was added Connection. on the west side of the double stair up to the Commandant’s quarters. These stairs were supported on eight piers. In 2005, the Commandant Gallery floor was repaired due to extensive termite damage and water damage from Hurricane Jeanne. It appears that water drainage issues were not resolved, and as noted above, this floor was again disassembled and rebuilt in 2015 by HPTC, with 70 percent of the wood elements replaced. Figure 21: Southwest Bastion, Exterior View. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Southwest Bastion Current Existing Construction The Southwest Bastion consists of heavy brick masonry exterior walls and brick masonry groin vaults supporting both the first floor and roof levels (observed from the basement and first floors respectively). As depicted in Fig. 21, two large masonry buttresses are battered in profile, widening toward the base, and are set near the middle of the walls at the south and west faces. A plan of the two levels of the bastion is shown on drawing E-1 with a section through the vaulting shown on drawing E-9. From the interior, the groin vaulting is seen to be coated with plaster. The vaults are formed from brick masonry. At the lower level, the groins integrate seamlessly with the surrounding walls and central pier (Fig. 22). At the upper level the center pier transitions to a more slender section above its base, and the load path to that pier is articulated with ribbed arches in the two cardinal directions (Fig. 23). Crack monitors and active cracking is apparent from this image and discussed in more detail below. At the roof level the surface rises up higher than the adjacent roof areas to the north (Fig. 24). The walls are typically on the order of 20” minimum thickness and the piers were measured to be on the order of 4 feet wide (out-of-plane from the line of wall) at the top. History of Structural Modifications / Repairs Per the 1960 HSR, the roof of the Southwest Bastion was originally built as a flat brick roof supported on timber joists. This roof was replaced between 1774 and Figure 22: Southwest Bastion, Lower Level. Figure 23: Southwest Bastion, Upper Level. Figure 24: Southwest Bastion Roof, Looking South. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report 1777 with the current vaulted brick construction. West Curtain Current Existing Construction The exterior wall to the west is approximately 2’-2” thick brick masonry, while the interior east wall that defines this side of the Interior Courtyard is approximately 1’-7” thick. The floor is on grade while the roof is framed with a mix of framing approaches. A site wall provides an additional line of the defense further to the west (Figs. 25 and 26). Rooms within the west curtain are separated by walls of varying thickness, some of which show intact half-timbered construction (Fig. 27). This approach has a long history dating back to medieval construction. The integration of wood with a masonry wall has the structural benefit of adding stronger tension- resisting elements into the masonry assemblies, which in general are strong in compression but weak in tension. This is particularly valuable in areas with significant lateral loading requirements, such as wind and seismic. Roof framing is indicated on drawings E-1 and E-2 and consists typically of a low north-south running girder that supports regularly spaced joists overtop. The girders are generally on the order of 8” x 10” and the joists typically 6” x 7 ½” spaced at 18” to 20” on center. Figure 25: West Curtain, East Façade. Figure 26: West Curtain, West Façade. Note West Site Wall and Northwest Bastion in Distance. Figure 27: West Curtain, Interior Half-timbered Wall, Room 14/15. Note Timber Roof Framing with Low Girder and Joists above. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report A number of joists and girders have apparently been repaired, with visible scarf joints at some locations (Fig. 28). A sample of these are noted in plan and depicted in drawing E-8. The Kitchen area presents an interesting change in roof construction, with the use of brick masonry vaulting within the western extension (Room 15) (Fig. 29). At the northern end of the west curtain the roof framing has been changed to reinforced concrete (Fig. 30), perhaps in response to more historic deterioration of wood framing. History of Structural Modifications / Repairs Per the 1960 HSR, the gun deck of the west curtain was shored in several places in 1824 due to rotten bearing ends of roof joists. In the early 1980’s significant repairs to the terreplein surfaces and to the wood framing below were implemented. In 2016-2017, HPTC rebuilt portions of the brick oven in the kitchen, whose inner arch had almost completely collapsed. Figure 28: West Curtain, Scarf Joint at Roof Joist. Figure 29: West Curtain, Kitchen. Figure 30: West Curtain, Reinforced Concrete Framing above Room 21. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Northwest Bastion and Latrine Current Existing Construction The Northwest Bastion is constructed of brick masonry vaulting. The construction is depicted in plan on drawing E-2 and in section on E-10. An overarching barrel vault spans from north to south within the bastion and is then divided at its midspan by a wall with arched openings (Fig. 31). This interior wall is approximately 2 feet thick while the exterior walls range from approximately 3’-7” to 4’-10”. At the roof level, the northwest corner is thickened to provide the structural base for the flagpole (Fig. 32). Extending north from the bastion is the latrine, with lower, buttressed, masonry walls that define the space as the land descends toward the shoreline (Fig. 33). The roof is wood-framed and surfaced with corrugated metal. As depicted in Fig. 34, the framing is light but well built, with inverted joist hangers tying down the metal roof and flatwise sleepers to the main rafters. The lightweight structure and immediate exposure to the shoreline render this roof susceptible to strong uplift forces from the wind. History of Structural Modifications / Repairs The flagpole in the North Bastion roof was repaired or replaced several times, once in 1991 after Hurricane Hugo and again in 2010 after Hurricane Omar. The Latrine Roof was replaced several times. It was reported in 1953 that portions of the roof were missing, and the 1959 HABS drawings showed the roof to Figure 31: Northwest Bastion, Room 22/23. Figure 32: North Bastion Roof, Note Flagpole. Figure 33: Latrine Roof. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report be entirely missing. The roof was replaced in 1983 and again in 1990 after Hurricane Hugo. Figure 34: Latrine, Underside of Roof Framing above Room 24C. Water Battery Current Existing Construction The Water Battery along the north side of the fort is a robust, heavy mass masonry construction mostly construction (Fig. 35). A group of nine groin vaults at the center, constructed of brick masonry, provides a strong support for the upper platform (Fig. 36). With short spans, robust piers, and ample mass and thickness above and to Figure 35: Water Battery, Looking Northwest. all sides, the structure was likely conceived with resistance to both heavy dead loads and potential artillery impacts. Figure 36: Water Battery, Vaulting at Room 25. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Typical of most areas at the top of the fort, the roof surface is covered with a cementitious parging over brick masonry pavers (Fig. 37). History of Structural Modifications / Repairs In 2020, HPTC removed vegetation from the Water Battery parapet. Figure 37: Water Battery, Brick Paving at Roof, Looking South towards Courtyard. Northeast Bastion Current Existing Construction Like the Northwest Bastion, the Northeast Bastion is spanned by a north-south barrel vault that is divided midspan by an interior wall with arched openings (Figure 38). A raised extension creates a second-floor Figure 38: Northeast Bastion, First Floor Level space that has an innovative approach (Room 1) with Vaulted Roof. to roof framing for the non-rectangular space. A kinked timber girder spans north-south, set below 4” x 10” rafters spaced approximately at 17” on center. The framing is shown in plan on drawing E-4 with details of the kinked beam on E-7 (Fig. 39). History of Structural Modifications / Repairs Per the 1960 HSR, the Bastion was extended vertically in 1836 to create a “Common Room.” The new flat brick roof Figure 39: Northeast Bastion, Room N at Second was supported on timber framing. Floor with Wood-framed Roof. Note Kinked Beam. After Hurricane Marilyn, it was noted in 1995 that the Common Room’s roof framing required modifications to address T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report wind uplift; however, it is unclear whether any repairs were made. East Curtain Current Existing Construction The exterior wall to the east is approximately 2’-4” thick brick masonry, while the interior east wall that defines this side of the Interior Courtyard is approximately 1’-8” thick. The floor is on grade. A site wall provides an additional line of the defense further to the east (Figs. 40 and 41). Roof framing is indicated on drawings E-1 and E-2 and consists of regularly spaced joists spanning in the east-west direction. The joists are typically 5 ½” x 7” spaced at 18” on center. These joists support 3”- wide by 2”-thick sleepers spaced at 4 ½” on center spanning in the perpendicular direction. These sleepers support roof boards which, in turn, support the flat brick roof. A similar construction exists in Room 7. In this area, previous repairs in the form of scarf joints were made (Fig. 42). At the west side of the east curtain a wood-framed shed roof provides a sheltered transition from the Courtyard (Fig. 40). The framing is depicted on drawing 1/E-7 and Figure 43. The light wood framing consists of 1-1/2” x 3” rafters spaced at 3’-4” on center, supported by a 2-3/8” x 2-5/8” primary wood member spanning over the west line of wood posts. The posts are 2-3/8” square and spaced at 8’-0” to 8’-6” on center. The full nature of the connections is somewhat hidden; however, it consists of a combination of metal fasteners and traditional timber-frame joinery. Roof joists have birdsmouth connections over Figure 40: East Curtain, West Façade facing Courtyard. Figure 41: East Curtain, East Façade Facing Stableyard. Figure 42: East Curtain Room 7, Existing Scarf Joint in Timber Roof Framing. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report the edge beams with blocking between joists to provide lateral stability (Fig. 44). West edge beams are connected to the posts below with pegged, mortise and tenon connections (Fig. 45), providing resistance against uplift. The east edge beam against the building wall is tied down to the wall with a metal connector (Fig. 46). History of Structural Modifications / Repairs Figure 43: East Curtain Shed, Underside of Roof. Per the 1960 HSR, in 1817-1818 rotted wood roof joists supporting the gun deck were replaced and the brick was relaid. In 1822, additional reconstruction of the east curtain was performed, including replacing the original half-timbered west wall with a thicker masonry wall. In 1826 the roof of the east curtain was covered with a layer of cement to mitigate the on- going leaks. In 1843, the gun deck was torn out and the timber roof joists were replaced due to rot. The gun deck was then relaid. Figure 44: East Curtain Shed, Edge Detail. In 1836 the zinc-covered shed on the courtyard side of the east curtain was constructed supported by eight hardwood posts. The floor below the shed consisted of bricks laid flat. In the early 1980’s significant repairs to the terreplein surfaces and to the wood framing below were implemented. Figure 45: East Curtain Shed, Beam to Post Connection. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Southeast Bastion Current Existing Construction The Southeast Bastion consists of heavy brick masonry exterior walls and brick masonry groin vaults supporting the roof level, as observed from the first floor. Similar to the Southwest Bastion, two large masonry buttresses are battered in profile, widening toward the base, and are set near the middle of the walls at the south and east faces. A Plan representation of the bastion is shown on drawing E-1. From the interior, the groin vaulting is seen to be coated with plaster. The vaults are formed from brick masonry. At the lower level, the groins integrate seamlessly with the surrounding walls and central pier. The load path to that pier is articulated with ribbed arches in the two cardinal directions (Fig. 47). Cracking is apparent from this image, similar but less severe than that observed at the Southwest Bastion. This is described in more detail below. History of Structural Modifications / Repairs Figure 46: East Curtain Shed, Hold-Down Detail. Figure 47: Southeast Bastion, Room 8, Brick Vaulting Supporting Roof. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Per the 1960 HSR, the roof of the Southeast Bastion was originally built as a flat brick roof supported on timber joists, per the 1960 HSR. This roof was replaced in between 1781 and 1782 with the current vaulted brick construction. In 1836 a wood shingle-covered shed was installed on the roof of the Southeast Bastion connected to the east wall of the south curtain. Stables Current Existing Construction The Stable is a long, narrow one-story brick masonry building approximately 123 feet long by 17.5 feet wide (Fig. 48). Its west wall is approximately 1’-8” thick with a series of large, arched openings (Fig. 48 and 49). The east wall is approximately 2’- 3” thick and punctured with small windows (Fig. 50). The south and north wall are approximately 2’-0” thick. Neither one has any openings currently, although the north wall has a previous arched opening which has been infilled (Fig. 49). The roof is a flat brick roof supported on wood sleepers and wood joists (Fig. 50). The roof joists were measured to be 5- 1/2” square and spaced at 13” to 18” on center. A roof framing plan is provided on drawing E-5. History of Structural Modifications / Repairs Per the 1960 HSR, the original stable was built between 1836 and 1837 and was 74’ long with six arched openings on the west façade. It had a flat brick roof supported on timber framing. The floor was paved with bricks, some of which were replaced with stone in 1839. Figure 48: Stable and Stableyard, Looking East at West Façade. Figure 49: Stable, Looking South at North Façade. Figure 50: Stable, Looking East at Interior Face of East Wall. Note Wood Roof Framing. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report In 1840 the stable was extended 25’ towards the north to accommodate laundry functions. In 1844, another addition approximately 21’ long was built at the north end of the stable for a second carriage house. The southern portion of the stable was also partitioned for a granary at that time. By 1978, large portions of the stable roof were missing or damaged and the roof was replaced in 1978-79. The new roof consisted of two layers of thin Danish brick and a rigid underlayment sandwiched between, all supported on wood framing. By 2013 the roof was determined to have “critical structural failure,” presumably due to considerable termite and water damage. The roof was once again replaced, this time in two phases. During Phase 1 in 2015-2017, the previous roof was removed in its entirety and all wood framing was replaced with green, pressure treated pine. Framing was attached to a top plate which was anchored into the masonry walls below. A temporary plywood roof was then installed over top of the framing. During the course of the work, it was discovered that the masonry walls and rafter pockets were damaged and these were rebuilt. Phase 2 was performed in 2015 and consisted of replacing the temporary roof with a new roof consisting of one layer of brick adhered to concrete roof panels with epoxy. The added weight of this system required modifications of the roof framing. Carriage House Current Existing Construction The Carriage House was built with brick masonry exterior load-bearing walls. The Figure 51: Carriage House, Looking South. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report south wall is approximately 2’ thick while the other three walls are thinner, measuring approximately 1’-6”. The west side of the structure connects to the Ravelin as well as the East Site Wall. The roof is a flat brick roof supported on wood sleepers and wood roof joists. The joists were measured to be 2-3/4” wide by 5-3/4” deep spaced at 15” on center. A roof framing plan is provided on drawing E-5. History of Structural Modifications / Repairs Per the 1960 HSR, the combined watchman’s room – carriage house was built between 1836 and 1837. It had a flat brick roof supported on timber framing. The Carriage House was reroofed in 1977 using salvaged bricks. Site Structures Current Existing Construction Site structures consist of the West and East Site Walls which flank the west and east curtains, described above. These walls, in addition to several other site structures, extend towards and even into the water on the north side of the site (Fig. 53 & 54). History of Structural Modifications / Repairs Per the 1960 HSR, the stone retaining wall on the west side of the stable yard was built between 1840 and 1841. In 1992, portions of the west and east wing walls were reconstructed after damage inflicted by Hurricane Hugo. Historic stone was salvaged for reuse in future projects and the wall was rebuilt with concrete block to differentiate the new from the earlier construction. Figure 52: Carriage House, Looking South within Interior. Note Wood Roof Framing. Figure 53: View of North Side of Site Facing Water. Note Various Site Structures. Figure 54: Looking East at West Site Wall. Note Continuation of Site Wall into Water. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Existing Conditions Existing conditions observed during 1200AE’s site visits on May 28 through May 30, 2021, and February 14 through February 15, 2022, are summarized below and follow the same order as the descriptions of the structural systems in the previous section. Observations start at the Ravelin Yard, continue with the south curtain, move counterclockwise from that location around the interior courtyard, and finish with the Stableyard and Site Structures. For room numbers and names, refer to Drawings 1 through 6 in Appendix C. Structural framing plans with annotated conditions and select sections and details are provided in Drawings E-1 through E-11 in Appendix E.1. All photographs are by 1200AE unless noted otherwise. Ravelin Shoring has been installed in the artillery shed (Room 27) to support deteriorated roof boards (Fig. 55). This deterioration is likely due to water infiltration through the roof. It appears that the leak has been repaired. Recommendation: Replace the roof boards for one bay. Sister or replace the rafter up against the wall. This will also require some roofing / flashing repair or replacement. The roof framing above Room 27 is of small dimensions and is spaced far apart, at approximately 3’-10” on center. Preliminary analysis of these rafters (using assumed material properties in the absence of wood identification and grading) indicates that the live load capacity of these rafters is on the order of only 8 pounds per square foot. This is not sufficient to meet current load requirements. In addition, it is unclear whether the rafter ends are adequately tied down to resist wind uplift loads (Fig. 56). Recommendation: Install one or two intermediate rafters in each rafter bay, pending further analysis. Install tie-downs at rafter ends. Figure 55: Ravelin Artillery Shed (Room 27), Deteriorated and Shored Roof Boards (JKOA). Figure 56: Ravelin Room 27, Rafter Bearing Condition at Low End. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report South Curtain – First Floor Spaces and Second Floor Framing The rooms below the exterior stairs on the north side of the south curtain are built with barrel vaults supporting the stairs above. The brick masonry and mortar in these vaults are showing signs of deterioration, likely due to long-term water infiltration through the stairs above (Fig. 57). Recommendation: The vaults appear structurally stable; however, surface Figure 57: South Curtain First Floor, Deteriorated Masonry in Room 26 below Stairs. deterioration of brick units and mortar can accelerate over time and lead to future structural weakening. The transmission of water through the stairs above should be minimized where possible, through localized joint treatments or potential resloping of surfaces to assure water can run off and is not trapped. At the intrados of the vaults, repointing is recommended at deteriorated areas and consideration of applying a parge coat to help minimize further losses of brick units. The wood floor and supporting joists/ sleepers at the south-facing rooms in the south curtain are heavily deteriorated (Fig. 58). They are in direct contact with the ground, which dramatically increases the moisture contact of the wood, a condition favorable to wood rot and termites. Recommendation: Wood in direct contact with earth is subject to accelerated deterioration from both Figure 58: South Curtain First Floor, Deteriorated moisture and easy access for termites Wood Floor in Room 12. and other insects. If public access is to be allowed, lift wood boards and salvage intact material for reuse. Install a reinforced concrete slab on grade at an elevation deep enough to allow room for application of wood sleepers and finish T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report wood flooring at the current elevation. Reinforcement in the slab on grade should be corrosion resistant, with consideration of both galvanized and stainless-steel wire mesh. If public access is not to be allowed, then the existing condition can remain as is. The second-floor framing above Room 12 was found to have evidence of termite damage (Fig. 59). Field documentation of exposed areas estimated the amount of loss to the 7” x 8” beams to be on the order of 1” from the top surface, for the southern third of the span. The floorboards were previously replaced and are currently supported on wood sleepers set on top of the beams. The sleepers are intermittently attached to the beams and some gaps in their support are likely causing flexibility in the floor surface above. Recommendation: Termite treatments should be updated at regular intervals to assure that infestations are not active. Preliminary calculations based upon the observed dead load and a 60 psf live load find the magnitude of loss to warrant reinforcement of the framing. Refinement of these findings is warranted, given the limited access, and the need for reinforcement may be limited to a portion of the beam span. It is assumed that reinforcement would be in the form of sistering new timber alongside the existing framing. As the current floorboard support is inconsistent, sistering the beams could also provide a more continuous and direct support of the floorboards, thereby providing both added beam capacity and continuous board support. Figure 59: South Curtain Second Floor Framing above Room 12. Note Termite Damage and Sleeper Discontinuity. Figure 60: South Curtain Second Floor, Termite Trails on Wall Leading up to Roof Framing. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report South Curtain – Second Floor Spaces and Roof Framing Termite trails were noted on wall surfaces in the Commandant’s Gallery at several locations (Fig. 60). These trails lead up the walls towards the roof framing. Recommendation: Termite treatments should be updated at regular intervals to assure that infestations are not active. Evidence of water infiltration through the roof and resulting deterioration of wood framing was noted in several locations within the Commandant’s Gallery. One such location is at the northwest corner of Room M and the adjacent space at the west end of the corridor (Fig. 62 and 63). At this location, there is a scupper to drain the rainwater from the roof. It is likely that the scupper does not drain adequately and has caused water to back up and enter the building through the exterior wall and / or roof. Recommendation: Roofing and drainage systems should be reviewed to ensure that the roof is watertight and the scupper is functioning as intended. After any necessary roofing repairs have been made, deteriorated wood members should be replaced in kind, either full length or partial length with an engineered scarf joint. Commandant’s Gallery Roof Severe deterioration of the low timber girder in the center bay of the Commandant’s Gallery was noted during 1200AE’s initial site visit (Fig. 63). Deterioration was found to be particularly severe at the east end of the girder. The root cause of this deterioration is likely water ingress from the roof associated at least in part with problems of the flashing Figure 61: South Curtain Roof Framing with Water Damage, Room M. Figure 62: South Curtain Roof Framing with Water Damage, Corridor Adjacent to Room M. Figure 63: South Curtain Gallery, Heavily Deteriorated Roof Girder. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report around the flagpole immediately above. The flagpole no longer projects above the roof and the roofing appears to have been repaired such that water is no longer penetrating the roof at this location. 1200AE recommended that temporary shoring be installed to provide safe access to the Gallery and adjacent spaces for staff and the public and provided engineered drawings for this shoring. Subsequently, 1200AE visited the site again to perform probing of the girder and its bearings to assess the remaining intact portions of wood and recommend options for repair or replacement of the girder. The girder was found to be built up with four separate members connected to each other with ferrous elements (Fig. 64). In the areas of heavy deterioration of the wood, the connectors were also noted to be heavily corroded. Wood testing indicated that the existing girder species is Southern Pine. A more detailed report of the girder assessment is provided in Appendix E.2. Recommendation: Based on the findings of the girder assessment, the southern ply of the girder should be replaced in kind. Connectors between plies will require replacement and reinforcement. A small area of the lower plies at the west end will require wood consolidation. Final design of the repairs was issued on January 23, 2023. South Curtain – Embedded Ferrous Elements Rusting of iron embedments in masonry, including window bars as well as window and door framing anchorages was prevalent. In some areas the deterioration of the iron was coincident Figure 64: South Curtain Gallery, Heavily Deteriorated Roof. Note Corroded Connectors. Figure 65: South Curtain, Embedded Corroded Ferrous Element. Figure 66: South Curtain, Embedded Corroded Ferrous Element. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report with significant wood deterioration, or complete loss of wood components (Fig 65 & 66). Other areas were clearly in an earlier phase of deterioration, with iron fasteners beginning to rust and starting to cause damage to surrounding materials (Fig. 67). As iron or steel rust in the presence of water and oxygen, the chemical process results in the volumetric expansive production of iron oxide. This expansive process can exert large forces on the surrounding materials. Figure 68 shows an apparent case of rusting embedded anchors that is damaging the surrounding wood and masonry, with incipient failures in both. Recommendation: Iron or steel anchorages should be replaced with structurally equivalent stainless steel to assure proper durability in the marine environment. Given the proximity of salt water, stainless steel Type 316 is recommended. Embedded iron or steel that is not deteriorating actively may be susceptible to future deterioration; however, replacement may be deferred, and the areas visually monitored over time to assure conditions do not change. South Curtain – Shed Roof The second-floor porch on the east side of the south curtain has a wood-framed, corrugated metal covered shed roof. As opposed to the heavy flat brick roofs in other areas, where the weight of the brick resists wind uplift during heavy wind events, this shed roof is of much lighter construction. Wind uplift is resisted by roof connections down to the wood rafters and tie-downs of the roof rafters to the wood beams and posts below. Edge beam to wood post connections are assumed to consist of pegged mortise and tenon connections, possibly with ferrous connectors in lieu of wood Figure 67: South Curtain, Embedded Corroded Ferrous Element in Wood Frame. Figure 68: South Curtain Gallery, Embedded Steel with Adjacent Incipient Spall in Masonry. Figure 69: South Curtain Shed, Post Crack at Beam to Post Connection. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report pegs. Some cracking was observed in the wood at these connections (Fig. 69), possibly indicating either corrosion of the ferrous connector or overstress in the wood. In addition, at the south end of the roof, the edge beam was observed to be pulling away from the south curtain wall (Fig. 70). This behavior is consistent with roof shifting or uplift due to high wind loads. Recommendation: Tie-downs and connections should be evaluated, although they currently appear to have performed relatively well over time. As the severity of storms and, as a result, wind loads are predicted to increase with the warming climate, this evaluation should take into account these anticipated changes. It is likely that connections will require some reinforcement in the form of added fasteners or connector plates. Added materials should be selected for the marine environment, with stainless steel typical for metal fasteners and connectors. Southwest Bastion The windows of the basement rooms are protected with steel or iron bars embedded in the surrounding masonry. These bars are corroding (Fig. 71). As noted above, when ferrous elements corrode in the presence of moisture and oxygen, they expand volumetrically, exerting large pressures against the surrounding materials. This typically causes cracking, crushing and/or displacement of these materials. Recommendation: The bars are likely still needed for both safety and historical reasons. As such, we recommend replacing the bars in kind with stainless steel and repairing surrounding masonry. If these elements are deemed to no Figure 70: South Curtain Shed, Separation of South Edge Beam from Wall. Figure 71: Southwest Bastion, Basement Window, Corroding Bars and Spalling Masonry. Figure 72: Southwest Bastion, First Floor. Note Cracking at Pier (Red Arrows). T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report longer be needed, remove bars from walls and repair masonry in kind with appropriate mortar. Extensive cracking in the masonry vaulting in the Southwest Bastion was observed from within the first-floor spaces, at the underside of the roof. Crack patterns are indicative of outward movement in masonry walls and piers, and corresponding flattening of the arches and vaults, associated with the horizontal thrust imposed by the primary arches and groin vaults (Fig. 72 & 73). In broad terms, as vertical load is applied to vaults and arches these structures carry that weight through compression along the lines of their raised profiles. For these structures, the rise of the vaults and arches provide the geometric stiffness to accommodate the large weights. These compressive forces must then be resisted at the base of the vaults and arches, both vertically and horizontally. When insufficient resistance to these forces is present, the vaults and arches will spread or settle, generally resulting in cracking. Crack gauges were installed prior to the current survey as a means to monitor and measure any movements after the installation of the gauges. Assuming that the gauges were all installed to be with the standard zero setting, movement has been observed at several locations (Fig. 74). Several of the gauges indicated no movement, remaining at the zero- movement mark. In one area, plaster was noted to have fallen from a line of cracking in a primary arch (Fig. 75) with plaster dust and fragments observed on the beds below (Fig. 76). This provided a clear sign of recent, on-going movement. Based on the 1960 HSR, the roof of the Southwest Bastion was originally built as a Figure 73: Southwest Bastion Exterior Cracking at Base of Wall, SW Corner. Figure 74: Southwest Bastion, Crack Gauge Indicating Movement (Rotation). Figure 75: Southwest Bastion, Recent Plaster Loss at Crack. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report brick flat roof supported on timber framing. This framing system would not have imposed horizontal thrust on the walls below, only vertical loads; however, the wood framing would have been more susceptible to rot and termite damage in the presence of moisture over time. The brick roof and wood framing were replaced with brick groin vaults, which likely provided better protection against water infiltration but did exert a horizontal thrust on the walls below. Recommendation: Since movement has been documented to be active and the observed conditions clearly support that data, a more detailed structural investigation and the design of repairs is warranted. Given the presence of the large exterior piers, the overall mass of the walls and vaulting, and the long history of the vaults remaining in place, an imminent structural failure does not seem likely. It is more likely that movements will advance slowly over time. As such, having this space continue to operate with the public having partial access near the entrance is deemed acceptable while further evaluation and likely strengthening is pursued. Structural analysis should provide a quantified assessment of the vault loads and thrust on the perimeter walls. The exterior masonry piers should be evaluated to resist these forces. Strengthening may consist of grouted anchorage of the exterior wall and piers to the roof and second-floor diaphragms, with potential vertical reinforcement of the exterior piers. Grouted anchorage may be in the form of extended stainless-steel anchors set in a grouted sock, with the grout engaging and keying into irregularities and/or voids in the masonry. Figure 76: Southwest Bastion, Recent Plaster Loss at Crack. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report West Curtain Some of the wood framing has suffered from both water and insect damage historically, with residual evidence of deterioration as well as areas of both full member replacement and repairs with traditional scarf joints for partial member replacement (Fig. 77). Recommendation: Address any active areas of water penetration to reduce potential for ongoing accelerated deterioration of wood framing. Cracking was observed at the underside of the reinforced concrete roof framing just south of the Northwest Bastion (Fig. 78). This is likely due to long-term water infiltration causing corrosion of the steel reinforcing at the bottom of the concrete beams. As noted previously, like steel or iron embedded in masonry, when steel reinforcement in concrete corrodes in the presence of moisture and oxygen, it expands volumetrically, exerting large pressures against the surrounding materials. This typically causes cracking, crushing and/or displacement of these materials. The observed cracking will likely continue and eventually result in spalling of the concrete below the reinforcing bars. At this point, the concrete below the bars would eventually break off and fall to the floor. Although this would not likely coincide with a catastrophic failure of the roof structure since the bars typically would remain in place, the falling concrete itself could represent a risk to visitors. Recommendation: Remove loose concrete. Expose corroded reinforcing bars, clean of all corrosion and coat with a rust-inhibiting coating. Patch concrete with a trowel-on patching mortar. Figure 77: West Curtain, Scarf Joint in Framing Member to Address Previous Deterioration. Figure 78: West Curtain, Cracked Concrete Beam. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Northwest Bastion Directly to the south of the latrine, in the Northwest Bastion, embedded ferrous elements have caused deterioration in the masonry walls (Fig. 79). As noted above, when ferrous elements rust in the presence of moisture and oxygen, they expand volumetrically, exerting large pressures on the surrounding materials. This has caused spalling of these materials. These elements do not appear to serve a structural function and appear to be abandoned and no longer needed. Recommendation: Remove ferrous elements from walls and repair masonry in kind with appropriate mortar. The vaulting of the Northwest Bastion generally appears in good structural condition. A line of cracking was noted, running parallel to the span of the main north-south barrel vault (Fig. 80). That this crack is running parallel to the span, as opposed to being transverse, leaves the vault form and original load path structurally intact without indication of movement relating to horizontal thrust. The crack may relate to some past movement of the exterior wall or localized discontinuity in the construction; however, it does not impede proper structural functioning of the vault. Recommendation: Localized repointing of crack and repair of finishes. If crack re- emerges then some form of long-term monitoring may be warranted, similar in nature to what has been done at the Southwest Bastion. Figure 79: Northwest Bastion, Corroded Elements. Figure 80: Northwest Bastion, Crack in Vault. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Latrine The latrine window has embedded ferrous bars that have caused damage to the masonry wall (Fig. 81). When ferrous elements rust in the presence of moisture and oxygen, they expand volumetrically, exerting large pressures on the surrounding materials. This has caused localized damage of the surrounding materials and represents an ongoing mechanism of deterioration that will continue to worsen. Recommendation: The bars are likely still needed for both safety and historical reasons. As such, we recommend Figure 81: Latrine, Corroded Bars. replacing the bars in kind with stainless steel and repairing surrounding masonry. The latrine roof is a light corrugated metal roof supported on wood framing. While there are no visible signs of distress, this type of roof is vulnerable to high wind uplift forces during severe weather events. Recommendation: Tie-downs and connections should be evaluated, although they currently appear to have performed relatively well over time. As the severity of storms and, as a result, wind loads are predicted to increase with the warming climate, this evaluation Figure 82: Latrine, Underside of Roof. should take into account these anticipated changes. Some connection reinforcement with stainless steel fasteners or connectors is likely, pending a detailed structural analysis. Water Battery The structure of the Water Battery was found to appear in good condition where accessible. No structural treatments are required. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Northeast Bastion The masonry structure of the Northeast Bastion was found to appear in good condition. No structural treatments are required. The roof framing appears to have suffered some damage historically, with some rafters being repaired with bolted half-lapped joints. The bolt heads are covered with wood plugs and the repairs appear to be functioning well over time. Surface rusting of iron anchors at the kinked center beam was observed (Fig 83 Figure 83: Northeast Bastion, Kinked Roof Beam. & 84). The rusting does not appear to be compromising the structural functioning of the framing. Recommendation: Scrape the iron of paint and loose materials, and recoat with an appropriate coating for the marine environment, in-keeping with the historic appearance. East Curtain The first-floor porch on the courtyard side Figure 84: Northeast Bastion, Corroded Connectors of the east curtain has a wood-framed, at Kinked Roof Beam. corrugated metal covered shed roof (Fig. 85). As opposed to the heavy flat brick roofs in other areas, where the weight of the brick resists wind uplift during heavy wind events, this shed roof is of much lighter construction. Wind uplift is resisted by roof connections down to the wood rafters and tie-downs of the roof rafters to the wood beams and posts below. Edge beam to wood post connections are observed to consist of pegged mortise and tenon connections, possibly with the addition of ferrous connectors in Figure 85: East Curtain Shed, View of Framing. lieu of wood pegs in some areas. Recommendation: Similar to the shed roof at the south curtain second floor, tie- downs and connections should be T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report evaluated, although they currently appear to have performed relatively well over time. As the severity of storms and, as a result, wind loads are predicted to increase with the warming climate, this evaluation should take into account these anticipated changes. It is likely that connections will require some reinforcement in the form of added fasteners or connector plates. Added materials should be selected for the marine environment, with stainless steel typical for metal fasteners and connectors. In Room 7, some of the wood roof framing has suffered from both water and insect damage historically, with residual evidence of deterioration as well as areas of both full member replacement and repairs with traditional scarf joints for partial member replacement. Some deterioration was still present in the roof boards (Fig. 86). Recommendation: Address any active areas of water penetration to reduce potential for ongoing accelerated deterioration of wood framing. Southeast Bastion Similar to the observations at the Southwest Bastion, extensive cracking in the masonry vaulting was observed from within the first-floor spaces, at the underside of the roof. Crack patterns are indicative of outward movement in masonry walls and piers, and corresponding flattening of the arches and vaults, associated with the horizontal thrust imposed by the primary arches and groin vaults (Fig. 87). The observations described for the Southwest Bastion are also applicable here, with a similar history of timber roof Figure 86: East Curtain Room 7, Split in Previous Scarf Joint Repair. Figure 87: Southeast Bastion, Crack in Vault. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report replacement with a heavier and thrust- inducing vaulted masonry roof system. Recommendation: The observed cracking again appears to be active, with areas of delaminating plaster and/or masonry, particularly at the primary arches. This area is not currently accessible to the public and should remain that way until further analysis and repairs, similar to that recommended for the Southwest Bastion are performed. Like the Southwest Bastion, further deterioration would appear to most likely develop in a slow progression in the form of localized material loss, as opposed to catastrophic collapse. As such, occasional access by staff would be acceptable and temporary shoring is not currently recommended. Stable At the northern end of the Stable, there is visible outward displacement of the northwest corner at the spring point of the arches on the west façade (Fig. 88). Related to this outward movement, there is cracking visible at the interior face of that corner and of the north wall (Fig. 89). This cracking and movement is likely caused by the lateral thrust at the arch spring point and insufficient stiffness at the corner pier to resist this thrust. Recommendation: Further analysis of the arch system along the west wall of the Stable should be performed to support the development of some form of strengthening and stiffening of the northernmost bay. Given that this bay does not currently have a door opening and has some shelving on the interior, there is opportunity to infill the opening in a discrete manner that still expresses the arched profile on the exterior, and perhaps even keeps the wood lattice Figure 88: Stable West Elevation, Note Inflection Point at Northwest Corner (Red Arrow). Figure 89: Stable Interior View of Northwest Corner. Note Cracking (Red Arrow). T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report finish. An infill might consist of reinforced concrete block with a potential new footing at the existing threshold of the opening, depending on existing conditions below grade. An external augmentation of the pier in the form of a buttress is also a possible solution; however, it will have greater visual impact and likely require more complicated foundations given the slope of the grade and the proximity of the shoreline. The windows in the east façade of the stable have embedded, corroding ferrous bars that have caused damage to the masonry wall (Fig. 90). As noted previously, when ferrous elements rust in the presence of moisture and oxygen, they expand volumetrically, exerting large pressures on the surrounding materials. This can cause crushing, cracking, or spalling of these materials, while also representing a loss of integrity to the metal itself. Recommendation: The bars are likely still needed for both safety and historical reasons. As such, we recommend replacing the bars in kind with stainless steel and repairing surrounding masonry. If these elements are deemed to no longer be needed, remove bars from walls and repair masonry in kind with appropriate mortar. Carriage House Some deterioration of wood framing was observed in areas of more recent water penetration at the Carriage House roof, east end. This correlates to open joints and vegetation observed in the flat brick roof above (Fig. 91), likely allowing water to penetrate into the building and cause the deterioration of the wood. Figure 90: Stable, Corroding Embedded Iron Bar at East Side Window. Figure 91: Carriage House Roof, NE Corner. Note Crack and Vegetation. Figure 92: Carriage House, Sill, and Roof Joist Deterioration at SE Corner. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report The sill and roof framing at the southeast corner of the building showed signs of rot (Fig. 92), as did the west bearing end of the lintel above the door opening (Fig. 93). Recommendation: Remove vegetation and repair brick roof to provide waterproof enclosure. After any necessary roofing repairs have been made, deteriorated wood members should be replaced in kind. Roof joists may be replaced full length or possibly partial length with an engineered scarf joint. A lapped joint should be provided for the sill replacement. Replacement wood should be suitable to the marine environment and contact with masonry for durability, although these members should not be subjected to extensive amounts of direct, sustained moisture. Site Structures The north side of the Fort and its site elements face the water and are more vulnerable to high wind, water, and flooding events. There is a history of strong hurricanes that have damaged the fort and its various site elements. Scour was observed at the base of the east (Fig. 94) and west seawalls. Erosion has exposed the base of the side walls of the site stair leading down to the water at the north end of the site (Fig. 95). The ground below the end of the east fort wall has also been eroded away, undermining the decorative masonry element (Fig. 96). Recommendation: Designs for localized underpinning of these projecting walls should be developed in coordination with a geotechnical investigation at the waterline. Underpinning may be in the form of surface-level concrete in combination with deeper pile Figure 93: Carriage House, Lintel Bearing Deterioration. Figure 94: East Seawall, Note Scour at Base. Figure 95: Site Stair, Note Scour / Soil Erosion (Red Arrow). T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report foundations, depending upon geotechnical findings. Projections of more intense weather events and rising sea levels should be taken into account in the design of the underpinning. Figure 96: Undermined Site Element at End of East Fort Wall. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Preliminary Structural Analysis As part of the review of the existing structure, 1200AE performed a preliminary structural analysis at locations of concern to understand possible sources of the existing distress observed in the field. This analysis was accomplished primarily with hand calculations using the following reference standards: • 2018 International Building Code (IBC), and referenced codes and standards including: o 2018 International Existing Building Code (IEBC) o Minimum Design Loads for Buildings and Other Structures (ASCE 7-16) o Flood Resistant Design and Construction (ASCE 24-14) o 2018 National Design Specification for Wood Construction (NDS) Given the nature of the structure and its location in a hurricane-prone zone by the sea, wind and flood loads are considered to be contributing to the ongoing mechanisms of deterioration. The following sources were consulted in regard to these types of extreme weather events: • Climate-Resilient Infrastructure: Adaptive Design and Risk Management, ASCE Manuals and Reports on Engineering Practice No. 140, edited by Bilal M. Ayyub, 2018. • The Secretary of Interior’s Standards for Rehabilitation & Guidelines for Flood Adaptation for Rehabilitating Historic Buildings, U.S. Department of the Interior, National Park Service, Technical Preservation Services, 2021. • FEMA Advisory Flood Hazard Resources Map, United States Virgin Islands, St. Croix, Map ID 0072, May 25, 2018. • U.S. Virgin Islands Mitigation Assessment Team (MAT) Report, FEMA P-2021, Hurricanes Irma and Maria in the U.S. Virgin Islands. Structural Loading and Serviceability 1. Risk Category The Risk Category of buildings and other structures for flood, wind, and earthquake loads is based on the building’s use or occupancy. Given that the building is currently used as office space for NPS staff and as a museum, the Risk Category based on ASCE-7 is Risk Category II. 2. Uniformly Distributed Live Loading The following values are specified by the applicable codes and standards or are higher values selected for use on this project. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Occupancy or Use Live Loadings Uniform Concentrated Assembly Areas and Terraces Offices Exhibit / Museum Spaces Metal Roofs Surcharge for Landscape Features 100 psf 50 psf 60 psf 20 psf 100 psf 300 lbs 300 lbs 300 lbs 300 lbs 3. Wind Loading The ASCE 7 Section on wind loads is used to calculate the design forces. The design base shear is found using the static force procedure with the following factors: Basic Wind Speed 165 mph (* See Special Wind Region below) Surface Roughness D (Water surfaces) Wind Exposure D Importance Factor (Iw) 1.0 Fort Christiansted is in a wind-borne debris region. ASCE 7 requires that wind speed-up effects at hills, ridges, and escarpments be included in the determination of the wind loads by using the Topographic Factor (Section 26.8 ASCE 7-16). The wind speed-up from topographic effects can produce significantly higher wind pressures than those calculated using the base design wind speed values. However, ASCE 7 topographic procedures are complex, and application is typically inconsistent. In response to 2017 Hurricanes Irma and Maria and in an attempt to provide a simplified alternative to determining the wind speedup effects, the Federal Emergency Management Agency (FEMA) in collaboration with the U.S. Virgin Islands Department of Planning and Natural Resources (DPNR) developed a set of new basic wind speed maps that include topography related speed-up effects referred to as the U.S. Virgin Island Special Wind Region. Special Wind Region Maps provide design wind speeds at one height above ground level (32.8 feet) and one terrain roughness exposure (Open terrain, Exposure C). Per the U.S. Virgin Islands Special Wind Region Maps (2019), the Basic Wind Speed including topographic effects is 172 mph. It has been proposed that the next edition of the USVI Building Code incorporate revised basic wind speed maps that consider topographic effects as an option for determining wind pressures on buildings and that these revised maps developed for the USVI should be included in the next edition of ASCE 7 (7-22). T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report 4. Seismic Loading The ASCE 7 Section on earthquake loads is used to calculate the design forces. The design base shear is found using the equivalent lateral force procedure with the following factors: Short Period Map Value (Ss) 82.0% g 1-Sec Period Map Value (S1) 30.6% g Site Class (soil factor) D (assumed, to be verified) 5% Spectral Response Acceleration (SDS) 65.6% g 5% Spectral Response Acceleration (SD1) 36.7% g Seismic Design Category D Basic Structural System Load-bearing masonry walls Seismic Resisting System Ordinary plain masonry shear walls Response Modification Factor (R) 1.5 5. Flood Loading Flood maps show how likely it is for an area to flood. Any place with a 1% chance or higher chance of experiencing a flood each year is considered to have a high risk. The excerpt of the FEMA flood map below indicates the flood risk in the area surrounding and including Fort Christiansvaern. Figure 97: Excerpt from 2018 FEMA Advisory Flood Hazard Resources Map, United States Virgin Islands, St. Croix, Map ID 0072. Red Arrow Points to Fort Christiansvaern. The areas north, east, and west of the fort are designated as Advisory Zone VE (ABFE: VE 1% EL 16-19), depending on the location. These are shaded in orange. The area south (inland) of the fort is designated as Advisory Zone AE (ABFE: AE 1% EL 15). These zones are shaded in blue. Per the ASCE-7 section on Flood Loads, these zones are defined as follows: T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report • Coastal V-Zone / High Hazard Area: An area within a Special Flood Hazard Area (SFHA), extending from offshore to the inland limit of a primary frontal dune along an open coast, and any other area that is subject to high-velocity wave action from storms or seismic forces. • Coastal A-Zone: An area within a special flood hazard area, landward of a V-Zone or landward of an open coast without mapped V-Zones. To be classified as a Coastal A-Zone, the principal source of flooding must be astronomical tides, storm surges, seiches, or tsunamis, not riverine flooding, and the potential for breaking wave heights greater than or equal to 1.5 ft must exist during the flood. The SFHA is defined as the land area covered by the floodwaters of a base flood. The elevation indicated is the Base Flood Elevation (BFE), which is the computed elevation to which floodwater is anticipated to rise during the base (1-percent-annual-chance) flood event. The ASCE 7 Section on flood loads defines flood-related design forces, which include the following: • Hydrostatic loads: loads caused by a depth of water to the level of the Design Flood Elevation (DFE). • Hydrodynamic loads: loads incorporating the dynamic effects of moving water. • Wave loads: loads that result from water waves propagating over the water surface and striking a building or other structure. • Impact loads: loads that result from debris or any object transported by floodwaters striking against buildings or other structures. ASCE 24 covers the design of structures to resist these flood-related design forces. Serviceability 1. Floor and Roof Deflections a) Floor deflection shall not exceed the following: • For floors supporting wood finishes: the floor live load deflection of wood beams and girders shall not exceed 1/360 of span lengths. Total deflection (dead + live) shall not exceed 1/240 of span lengths. • For floors supporting tile finishes or plaster ceilings: the floor live load deflection of wood beams and girders shall not exceed 1/480 of span lengths. Total deflection (dead + live) shall not exceed 1/360 of span lengths. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report b) Roof deflection shall not exceed the following: • For flat brick roofs on timber framing: under live or wind load shall not exceed 1/360 of the span length. Total deflection (dead + live) shall not exceed 1/240 of span length. • For sloped metal roofs on timber framing: under live or wind load shall not exceed 1/240 of the span length. Total deflection (dead + live) shall not exceed 1/180 of span length. Structural Material Specifications Existing Timber / Lumber Wood species identification was performed at the built-up girder supporting the roof at the center of the Commandant’s Gallery. This testing was performed by the Forest Service Center for Wood Anatomy Research of the U.S. Department of Agriculture. It was found that the wood is a species of Southern Yellow Pine, Pinus sp. As pine is not native to the Virgin Islands, it appears that this wood was imported. It was noted in the 2015 HPTC Historic Structure Treatment Record that deteriorated framing members in the south curtain were replaced with Mahogany during that program of repairs. Given that no additional testing or grading of other wood elements at the Fort was performed as part of this HSR, preliminary analysis of limited areas was based on the assumption of Southern Pine No. 1. For any future detailed analysis, this assumption should be confirmed by testing. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Conclusions and Recommendations Climatic Effects There is a history of severe hurricanes damaging elements of Fort Christiansvaern. Post-hurricane structural repairs were undertaken after each of those events and are summarized above. Recent hurricanes resulting in damage include Hurricanes Hugo (Category 4; September 17, 1989), Marilyn (Strong Category 2; September 15,1995), Omar (Category 3; October 15, 2008), and Irma / Maria (Category 5; September 6 and 20, 2017). The intensity and frequency of these hurricanes are anticipated to increase with the warming climate, and building codes are incorporating updated design parameters to reflect these changes. At Fort Christiansvaern, the implications of these more intense weather events include the following: • Higher wind loads associated with more intense storms impose larger uplift forces on roofs. This may not affect the heavier brick roofs on site; however, the lighter metal roofs and supporting framing may require additional analysis and more substantial tie-downs to prevent the roofs from being torn off during a heavy storm. • Flagpoles are also susceptible to wind damage and the flagpoles themselves and/or their attachments may require reinforcement for higher load scenarios. • Wind-borne debris can impact the building elements with a higher force in more intense storms. Windows are particularly susceptible to damage from wind-borne debris. The heavy masonry walls of the structure are more resistant to these forces but can also sustain damage. • Site elements near the shoreline are exposed to wave action and may experience higher forces, potentially causing more damage to these elements and their foundations. Scour has affected the foundations for these elements historically and this is anticipated to increase. Specific recommendations for building elements exposed to these forces are described in more detail below. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Stabilization and Repair Specific recommendations related to observed structural deficiencies have been described in detail in the Existing Conditions section of this report, including recommendations related to the changing climate. These recommendations are summarized briefly below: 1. Ravelin, Room 27: In shored area, replace the roof boards for one bay. Sister or replace the rafter up against the wall. Perform roofing and flashing repair or replacement. 2. Ravelin, Room 27: Preliminary analysis of roof framing yielded low load capacities. Install one or two intermediate rafters in each rafter bay, pending further analysis. Install tie-downs at rafter ends. 3. South Curtain, First Floor: Deteriorated brick masonry and mortar in barrel vaults below stairs. At stairs above, perform localized joint treatments or potential resloping of surfaces to assure water can run off and is not trapped. Repoint deteriorated areas at the intrados of the vaults and consider applying a parge coat to help minimize further losses of brick units. 4. South Curtain, First Floor: Deteriorated wood floor and supporting joists/ sleepers at the south-facing rooms. Wood in direct contact with earth is subject to accelerated deterioration from both moisture and easy access for termites and other insects. If public access is to be allowed, lift wood boards and salvage intact material for reuse. Install a reinforced concrete slab on grade at an elevation deep enough to allow room for application of wood sleepers and finish wood flooring at the current elevation. Reinforcement in the slab on grade should be corrosion resistant, with consideration of both galvanized and stainless-steel wire mesh. If public access is not to be allowed, then the existing condition can remain as is. 5. South Curtain, second-floor framing above Room 12: Framing found to have evidence of termite damage with significant section loss and inconsistent support of floorboards. Termite treatments should be updated at regular intervals to assure that infestations are not active. Remove finishes to fully expose extent of deterioration. Reinforce deteriorated beam(s) by sistering new timber alongside the existing framing. 6. South Curtain – Second Floor Spaces: Termite trails leading up the wall surfaces towards the roof framing surfaces in the Commandant’s Gallery at several T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report locations. Termite treatments should be updated at regular intervals to assure that infestations are not active. 7. South Curtain – Second Floor Spaces: Evidence of water infiltration through the roof and resulting deterioration of wood framing in several locations within the Commandant’s Gallery. Roofing and drainage systems should be reviewed to ensure that the roof is watertight and the scupper at west end of corridor is functioning as intended. After any necessary roofing repairs have been made, deteriorated wood members should be replaced in kind, either full length or partial length with an engineered scarf joint. 8. Commandant’s Gallery Roof: Severe deterioration of the low timber girder in the center bay of the Commandant’s Gallery. Temporary shoring should be installed per provided engineered drawings to provide safe access to the Gallery and adjacent spaces. Based on the findings of the girder assessment, the southern ply of the girder should be replaced in kind and connectors between plies replaced and reinforced. A small area of the lower plies at the west end will require wood consolidation. Final design of the repairs was issued on January 23, 2023. 9. South Curtain: Corroded ferrous elements embedded in masonry or wood. Replace iron or steel anchorages with structurally equivalent stainless steel (Type 316) to assure proper durability in the marine environment. Embedded iron or steel that is not deteriorating actively may be susceptible to future deterioration; however, replacement may be deferred, and the areas visually monitored over time to assure conditions do not change. 10. South Curtain – Shed Roof at second-floor porch: Evidence of behavior consistent with roof shifting or uplift due to high wind loads. Tie-downs and connections should be evaluated, although they currently appear to have performed relatively well over time. As the severity of storms and, as a result, wind loads are predicted to increase with the warming climate, this evaluation should take into account these anticipated changes. It is likely that connections will require some reinforcement in the form of added fasteners or connector plates. Added materials should be selected for the marine environment, with stainless steel typical for metal fasteners and connectors. 11. Southwest Bastion: Corroding steel or iron bars embedded in surrounding masonry at basement windows. Replace bars in kind with stainless steel and repair surrounding masonry. If these elements are deemed to no longer be T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report needed, remove bars from walls and repair masonry in kind with appropriate mortar. 12. Southwest Bastion Vaulting: Extensive cracking in masonry vaulting within the first- floor spaces with existing crack gauges installed to facilitate monitoring. Signs of on-going movement are evident, but an imminent structural failure does not seem likely. It is more likely that movements will advance slowly over time. As such, having this space continue to operate with the public having partial access near the entrance is deemed acceptable while further evaluation (structural analysis) and likely strengthening is pursued. Strengthening may consist of grouted anchorage of the exterior wall and piers to the roof and second-floor diaphragms, with potential vertical reinforcement of the exterior piers. Grouted anchorage may be in the form of extended stainless-steel anchors set in a grouted sock, with the grout engaging and keying into irregularities and/or voids in the masonry. 13. West Curtain: Some of the wood framing has suffered from both water and insect damage historically. Address any active areas of water penetration to reduce potential for ongoing accelerated deterioration of wood framing. 14. West Curtain: Cracking at underside of reinforced concrete roof framing just south of the Northwest Bastion. Remove loose concrete. Expose corroded reinforcing bars, clean of all corrosion and coat with a rust-inhibiting coating. Patch concrete with a trowel-on patching mortar. Address any active areas of water penetration. 15. Northwest Bastion - directly to the south of the latrine: Corroded ferrous elements with associated damage in the masonry walls in which they are embedded. Remove ferrous elements from walls and repair masonry in kind with appropriate mortar. 16. Northwest Bastion vaulting: Line of cracking running parallel to the span of the main north-south barrel vault. The crack does not impede proper structural functioning of the vault. Localized repointing of crack and repair of finishes. If crack re-emerges then some form of long-term monitoring may be warranted, similar in nature to what has been done at the Southwest Bastion. 17. Latrine: Corroded ferrous bars with associated damage in masonry wall in which they are embedded. The bars are likely still needed for both safety and historical reasons. As such, we recommend replacing the bars in kind with stainless steel and repairing surrounding masonry. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report 18. Latrine roof: Light roof construction is vulnerable to high wind uplift forces during severe weather events. Tie-downs and connections should be evaluated, although they currently appear to have performed relatively well over time. As the severity of storms and, as a result, wind loads are predicted to increase with the warming climate, this evaluation should take into account these anticipated changes. Some connection reinforcement with stainless steel fasteners or connectors is likely, pending a detailed structural analysis. 19. Northeast Bastion Roof: Surface rusting of iron anchors at the kinked center beam. The rusting does not appear to be compromising the structural functioning of the framing. Scrape the iron of paint and loose materials, and recoat with an appropriate coating for the marine environment, in-keeping with the historic appearance. 20. East Curtain - first-floor porch roof on the courtyard side: Light roof construction is vulnerable to high wind uplift forces during severe weather events. Tie-downs and connections should be evaluated, although they currently appear to have performed relatively well over time. As the severity of storms and, as a result, wind loads are predicted to increase with the warming climate, this evaluation should take into account these anticipated changes. It is likely that connections will require some reinforcement in the form of added fasteners or connector plates. Added materials should be selected for the marine environment, with stainless steel typical for metal fasteners and connectors. 21. East Curtain, Room 7: Some of the wood roof framing has suffered from both water and insect damage historically. Address any active areas of water penetration to reduce potential for ongoing accelerated deterioration of wood framing. 22. Southeast Bastion Vaulting: Extensive cracking in masonry vaulting within the first- floor spaces. Signs of on-going movement are evident, but an imminent structural failure does not seem likely. It is more likely that movements will advance slowly over time. This area is not currently accessible to the public and should remain that way until further analysis and repairs are performed. Occasional access by staff would be acceptable and temporary shoring is not currently recommended. Strengthening may consist of grouted anchorage of the exterior wall and piers to the roof and 2nd floor diaphragms, with potential vertical reinforcement of the exterior piers. Grouted anchorage may be in the form of extended stainless-steel anchors set in a grouted sock, with the grout engaging and keying into irregularities and voids in the masonry. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report 23. Stable – northern end: Outward displacement of northwest corner at the spring point of the arches on the west façade and related cracking at interior face of wall. Further analysis of the arch system along the west wall should be performed to support the development of a strengthening design. A potential solution is to infill the northernmost opening in a discrete manner that still expresses the arched profile on the exterior. Infill might consist of reinforced concrete block and a potential new footing at the existing threshold of the opening, depending on existing conditions below grade. An external augmentation of the pier, in the form of a buttress, is also possible; however, it will have greater visual impact and likely require more complicated foundations. 24. Stable – east facade: Corroded ferrous bars with associated damage in masonry wall in which they are embedded. The bars are likely still needed for both safety and historical reasons. As such, we recommend replacing the bars in kind with stainless steel and repairing surrounding masonry. If these elements are deemed to no longer be needed, remove bars from walls and repair masonry in kind with appropriate mortar. 25. Carriage House – Roof framing: Areas of water penetration at east end of roof with associated deterioration of framing, including sill and roof framing at southeast corner and west bearing end of the lintel above the door opening. Open joints and vegetation in flat brick roof above. Remove vegetation and repair brick roof to provide waterproof enclosure. After roofing repairs, replace deteriorated wood members in kind. Roof joists may be replaced full length or possibly partial length with an engineered scarf joint. A lapped joint should be provided for the sill replacement. Replacement wood should be suitable to the marine environment and contact with masonry for durability. 26. Site Structures: Scour and erosion at bases of seawalls and at site stair side walls and decorative masonry element. The north side of the Fort and its site elements face the water and are more vulnerable to high wind, water, and flooding events. There is a history of strong hurricanes that have damaged the fort and its various site elements. Designs for localized underpinning of these projecting walls should be developed in coordination with a geotechnical investigation at the waterline. Underpinning may be in the form of surface-level concrete in combination with deeper pile foundations, depending upon geotechnical findings. Projections of more intense weather events and rising sea levels should be taken into account in the design of the underpinning. T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Appendix E.1: Drawings E-1: Second Floor Framing on First Floor Plan – South E-2: Second Floor Framing on First Floor Plan – North E-3: Roof Framing on Second Floor Plan – South E-4: Roof Framing on Second Floor Plan - North E-5: Stable / Carriage House Roof Framing on Floor Plan E-6: Section Through First Floor Porch E-7: Section Through Second Floor Porch and Kinked Beam Details E-8: Scarf Joint Details E-9: E-W Section Through Southwest Bastion – Looking South E-10: Partial Building Sections Through West Curtain E-11: Partial Building Sections Through Stable T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com Date: Submission: Project Number: Project Title: 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS E-1 Date: Submission: Project Number: Project Title: 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS E-2 Date: Submission: Project Number: Project Title: 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS E-3 Date: Submission: Project Number: Project Title: 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS E-4 Date: Submission: Project Number: Project Title: 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS E-5 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: E-6 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: E-7 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: E-8 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: E-9 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: E-10 07-19-2023 HISTORIC STRUCTURE REPORT 20-131 FORT CHRISTIANSVAERN AND STABLE BUILDING HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: E-11 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Appendix E.2: Detailed Assessment of Timber Girder at Commandant’s Gallery T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com DETAILED ASSESSMENT OF TIMBER GIRDER AT COMMANDANT’S GALLERY 100% REPORT Date: May 2, 2022 Date(s) on site: February 14, 2022 Attention: Christopher Woollard, Assoc. AIA Project name: Fort Christiansvaern – Girder Assessment Company: Joseph K. Oppermann – Architect, P.A. (JKOA) 1200AE Proj. #: 20-131.2 Weather: Sunny, 75oF Location: St. Croix, USVI Submitted by: Nicole Ferran, PE John Matteo, PE Present on site: N. Ferran & J. Matteo (1200AE); Evan Gwilliam (NPS) Cc: Robert Hotes, Joseph Oppermann, File BACKGROUND Fort Christiansvaern is a brick, rubble masonry and half-timber structure located on the shoreline of Christiansted Harbor, St. Croix, U.S. Virgin Islands and is part of the Christiansted National Historic Site. The construction was begun in 1738 and largely completed by 1749. During the structural survey from 6/28/21 to 6/30/21, performed as part of the development of a Historic Structures Report, a primary timber girder at the Commandant’s Gallery was found to be severely deteriorated. 1200AE issued a memo dated 7/16/21 recommending that temporary shoring be designed and installed, with public access to the area being restricted until the work is completed. Drawings for the temporary shoring were issued by 1200AE on 3/23/2022. At the request of the National Park Service, 1200AE personnel performed a site visit on February 14, 2022 to conduct a detailed assessment of the timber girder, including hands-on documentation and probing of surface conditions, localized drilling with a small diameter bit to assess the integrity of interior wood material, and extraction of a wood sample for species identification. The intent of this review was to evaluate the extent of deterioration of the existing girder and make recommendations regarding its repair or replacement. Figure 1: Exterior view of the Commandant’s Gallery, looking South, with the area of study circled in red. T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM 2 of 6 Detailed findings with accompanying photographs and sketches as well as repair and / or replacement recommendations are provided below. FINDINGS FIGURES Geometry and Configuration The existing timber girder spans approximately 16.5 feet between masonry walls and supports a series of wood roof joists (Figure 2), which in turn support wood sleepers and a brick roof. The roof joists bear on the top surface of the girder, which slopes along its length to create the roof slope. A partial roof framing plan is provided on SSK-1, attached. The south face of the existing timber girder is exhibiting severe signs of deterioration, in particular at its east end (Figure 2). This deteriorated area facilitated observation of the girder by1200AE personnel, who accessed the girder by means of a tall ladder and discovered that the girder was, in fact, a built-up member comprised of four structural components and wood veneer on the three exposed sides. The two lower portions of the girder are approximately 6 inches wide by 7-1/2 inches tall. The two upper portions of the beam are the same width; however, the height varies along the span to create the roof slope. At the ends, the low points, the upper members are 3-3/4 inches tall and at the peak they are 7-3/4 inches tall. The veneer was approximately 1 inch thick on the sides and 3/4 inches thick at the bottom. A cross section is provided in Figure 3 and at a larger scale on SSK-2, attached. The plies are connected to each other by means of ferrous connectors. At the heavily deteriorated area, these could be observed approximately 2-1/2 feet from the east end of the girder (Figure 4). One vertical connector (red arrow) approximately 3/4 inches in diameter and one horizontal connector with a 1-1/4 inch square head (green arrow) were observed. Both were heavily corroded. Figure 1: Looking north at deteriorated timber girder Figure 3: Existing section through girder Figure 4: Existing connectors in deteriorated girder T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM 3 of 6 At the bearing ends, the girder pockets into the masonry walls. At the east bearing end, a crack was observed emanating from the corner of the roof joist above. 1200AE personnel drilled a hole into the stucco wall finish to confirm that this crack coincided with the end of the girder within the wall (Figure 5). Given the level of deterioration of the girder at this end, it appeared plausible that the embedded girder end would crush with the load of the roof joist above and cause cracking in the stucco finish. It was confirmed that this crack, located 16 inches from the end of the wall, coincided with the girder end. On the north face of the girder, remnants of a flagpole support can be seen at mid­ span of the girder (Figures 6 and 7). A 5”x5” post is connected to the girder with a 3/4” diameter thru-bolt and four additional screws through a 1/2”x2” bent plate. Where the wood post extends through the roof the typical wood sleepers and brick roof were replaced with a solid concrete section. The flagpole is no longer visible above the roof (Figure 1); however, a historic photograph thought to have been taken in 1953 still shows the flagpole present (Figure 8). The wood and metal fasteners appear to be in good condition at this location. Figure 5: East girder bearing condition. Note drill hole and crack in plaster finish coinciding with end of girder. Figure 6: Looking south at north face of the girder and the flagpole connection Figure 8: Exterior view of the Commandant’s Gallery, looking South, thought to have been taken ca. 1953 by Frederik Gjessing. Note presence of flagpole. Figure 7: Close-up view of the flagpole connection T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM 4 of 6 Existing Conditions As noted above and as can be seen in the photograph in Figure 2, severe deterioration of the existing girder was evident at the south face, east end of the girder. It is assumed that this deterioration is due to continued exposure to moisture, possibly from a previous leak at the roof penetration for the flagpole. The portion of the flagpole above the roof level has been removed and roof repairs have been performed, and it appears that there are no remaining roof leaks at this location (Figure 9). To evaluate the extent of deterioration or decay in the existing girder, 1200AE personnel used a drill with a small diameter drill bit to drill into the sides and underside of the girder at regular intervals (Figure 10). Where the drill entered the wood easily, the wood was deemed to be deteriorated. Where substantial effort was required to penetrate the wood with the drill, the wood was considered sound. While just a qualitative method, this manner of drilling facilitated mapping of deteriorated areas in the girder. The lower member of the southern ply was found to be the most severely deteriorated portion of the girder. Along the full length of the member, the lower south ply was found to have deterioration within up to 3­ 1/2 inches of the width, including the veneer (Figure 11) as well as at the east bearing, as noted above. At the upper member of the southern ply, the bottom inch of the eastern third was deteriorated, as was a small portion near the west end. In addition, a shear crack was visible near the east bearing end (Figure 12). This shear crack is likely due to the severe deterioration and crushing of the lower member, which has caused the bearing end of the upper member to be overstressed. Figure 9: Looking east at roof above girder. Figure 10: Drilling at east bearing end to evaluate soundness of wood. Figure 11: Resistance drilling at south face of girder. Screwdriver in drill hole indicates depth of deterioration. T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM 5 of 6 The northern ply was typically found to be in much better condition than the southern ply of the girder. The regular drilling pattern showed both the upper and lower members to be sound with the exception of the west bearing, where a small portion of the lower member exhibited deterioration near the center of the beam (Figures 13 and 14). The extent of the deterioration was limited to an area approximately 3 inches wide by 1-1/2 inches tall by 10 inches long. These conditions are documented in SSK-4 and SSK-5, attached. Wood Species Identification A small sample of wood from the southern plies was removed while on site and sent to a wood testing laboratory for species identification. Testing by the Forest Service of the U.S. Department of Agriculture found that the wood is a species of Southern Yellow Pine, Pinus sp. As pine is not native to the Virgin Islands, it appears that this wood was imported. As no dendrochronology was performed at this time, we are not able to confirm whether this member was part of the original construction or was a later addition. The detailing is historic in nature and appears consistent with other components of the framing. The results of the laboratory testing are provided in Appendix B. Preliminary Analysis A preliminary structural analysis of the wood girder was performed to evaluate the adequacy of its as-built geometry under current code-mandated loading. The girder was analyzed both as four individual members, neglecting their connections to each other, and as one composite member, assuming full connectivity between the four components. Figure 12: Shear crack at east end, upper girder member Figure 13: Looking south at north face of girder, west bearing. Red arrows indicate drilling locations. Figure 14: Underside of west bearing end of girder with drilled holes T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM 6 of 6 The analysis showed that the first approach, that of considering only an additive approach for four individual members, was not sufficient regardless of the existing or proposed wood species and grade. The required properties both for bending moment and for deflections exceeded typical values for timber. However, once the connectors were taken into account and the member was analyzed as a composite section, it was found that a range of wood types and grades would be sufficient to resist the current loading scenarios. Recommendations The deteriorated girder should be shored to allow safe visitor access to the areas surrounding the Commandant’s Gallery. Shoring should remain in place during the girder replacement / repairs (see below). Temporary shoring drawings were issued by 1200AE on 3/22/2022 and are provided in Appendix C for reference. Given the poor condition of the southern ply of the girder, we recommend that the entire southern ply be replaced to match the existing in geometry. Based on the findings of the preliminary analysis, rot-resistant wood with the following minimum properties should be used. Note that this assumes composite action between the girder components and a maximum deflection of 1/360 of the girder span. Emin = 900,000 psi fb = 900 psi fc (perp.) = 100 psi fv = 100 psi White Oak No. 1 or pressure treated Southern Pine No. 1 both meet these requirements, among others. The final selection of replacement wood and the final design should include an evaluation of relative stiffness between new and old to assure compatible structural interaction. In order to remove the deteriorated ply, existing screws / connectors between the northern and southern plies will need to be removed or cut. New connections will be required after replacement of the deteriorated ply. Type and frequency of connectors will be determined as part of the final repair design. For the northern ply, only a small area at the west bearing was found to be deteriorated. For this area, localized epoxy repairs would be an appropriate repair. It may be prudent to provide additional connectors between the upper and lower northern plies to ensure full composite behavior. We recommend repairing this side of the girder, as opposed to replacing it in full, because it is in-keeping with an approach to maximize the retention of historic structural fabric, including the detailing of the flagpole connection which serves as an interpretable artifact of this former feature. There is also a likely cost savings with this approach. The existing wood veneer was found to be deteriorated at the south face and underside of the beam. We recommend replacement in kind once the structural repairs are complete, matching the existing thicknesses and profiles. If you should have any questions or concerns related to the content of this report, please feel free to contact us at (703) 350-4151. T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM APPENDIX A: STRUCTURAL SKETCHES T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM 04/15/22 REPORT 20-131.2 FORT CHRISTIANSVAERN GIRDER ASSESSMENT SSK-1 ST. CROIX, VI Date: Submission: Project Number: Project Title: 04/15/22 REPORT 20-131.2 FORT CHRISTIANSVAERN GIRDER ASSESSMENT SSK-2 ST. CROIX, VI Date: Submission: Project Number: Project Title: 04/15/22 REPORT 20-131.2 FORT CHRISTIANSVAERN GIRDER ASSESSMENT SSK-3 ST. CROIX, VI Date: Submission: Project Number: Project Title: 04/15/22 REPORT 20-131.2 FORT CHRISTIANSVAERN GIRDER ASSESSMENT SSK-4 ST. CROIX, VI Date: Submission: Project Number: Project Title: 04/15/22 REPORT 20-131.2 FORT CHRISTIANSVAERN GIRDER ASSESSMENT SSK-5 ST. CROIX, VI Date: Submission: Project Number: Project Title: 04/15/22 REPORT 20-131.2 FORT CHRISTIANSVAERN GIRDER ASSESSMENT SSK-4 ST. CROIX, VI Date: Submission: Project Number: Project Title: APPENDIX B: WOOD TESTING REPORT T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM APPENDIX C: TEMPORARY SHORING DRAWINGS T: (703) 350-4151 210 NORTH LEE STREET, SUITE 210, ALEXANDRIA, VA 22314WWW.1200AE.COM 5-3-2022 TEMPORARY SHORING 20-131.1 FORT CHRISTIANSVAERN HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: SSK-1 5-3-2022 TEMPORARY SHORING 20-131.1 FORT CHRISTIANSVAERN HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: SSK-2 5-3-2022 TEMPORARY SHORING 20-131.1 FORT CHRISTIANSVAERN HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: SSK-3 5-3-2022 TEMPORARY SHORING 20-131.1 FORT CHRISTIANSVAERN HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: SSK-4 5-3-2022 TEMPORARY SHORING 20-131.1 FORT CHRISTIANSVAERN HOSPITAL STREET CHRISTIANSTED, ST. CROIX 00820 U.S. VIRGIN ISLANDS Date: Submission: Project Number: Project Title: SSK-5 20-131 Fort Christiansvaern and Stable Building – Historic Structure Report July 19, 2023 Appendix E: Structural Report Appendix E.3: Existing Drawings T: (703) 350-4151 210 North Lee Street, Suite 210, Alexandria, VA 22314 www.1200ae.com Appendix F: Materials Analyses Report by BCA Fort Christiansvaern Materials Analyses Christiansted, U.S. Virgin Islands FINAL (Revised July 20, 2023) _rfiafkd=`lkpbos^qflk=^ppl`f^qbp=fk`= Fort Christiansvaern Materials Analyses Christiansted, U.S. Virgin Islands FINAL (Revised July 20, 2023) Prepared For Joseph K. Oppermann Architects Winston-Salem, North Carolina Prepared By Building Conservation Associates, Inc. 242 Cherry Street Philadelphia, Pennsylvania 19106 CONTENTS 1.0 INTRODUCTION .........................................................................................1 2.0 BACKGROUND INFORMATION.............................................................4 3.0 METHODOLOGY ..........................................................................................7 4.0 IN SITU OBSERVATIONS ............................................................................8 4.1 Masonry Materials (Mortar, Plaster, Stucco)...................................8 4.2 Finishes .....................................................................................................15 5.0 LABORATORY ANALYSIS...........................................................................16 5.1 Masonry (Mortar, Plaster, Stucco).....................................................16 5.2 Finishes .....................................................................................................20 6.0 CONCLUSIONS & RECOMMENDATIONS...........................................39 APPENDICES Appendix A: Previous Materials Analyses Reports Appendix B: Existing Floor Plans with Room Names/Numbers Used by BCA Appendix C: List of Sample Locations Appendix D: Photomicrographs and Stratigraphy Charts of Finish Samples Appendix E: Mortar Analysis Report (Highbridge Materials Consulting) Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 1.0 INTRODUCTION At the request of Joseph K. Opperman Architects (JKOA), Building Conservation Associates, Inc. (BCA) has prepared an analysis of historic building materials of Fort Christiansvaern, located at the Christiansted National Historic Site in Christiansted, St. Croix in the U.S. Virgin Islands. (Figures 1-3) This study provides information about the fort’s historic mortar, plaster, and stucco, as well as paint finishes of select architectural elements. It will revisit the findings of prior materials analyses and make recommendations for repair mixes for the materials examined based on the results of the laboratory analysis. The goal of the materials analyses is two-fold: one, to ensure that physically and visually compatible repair mixes are being used for contemporary repair campaigns; and two, to confirm the accuracy of prior materials analyses studies, especially in relation to the fort’s appearance over time. Following introductory information and a discussion of the materials analysis methodology, the report is organized into two primary sections. Section 4.0 summarizes the in-situ observations of both masonry and paint materials and Section 5.0 summarizes the results of the laboratory analysis. All photographs included in the report were taken by BCA unless otherwise noted. All mounted paint cross-sections will be permanently housed at BCA’s Philadelphia office. All work required for this study was performed by Dorothy Krotzer, Director. BCA performed a site visit and removed paint and masonry material samples in June 2021 and analyzed the samples from August 2021 through October 2022. For the execution of this study, BCA collaborated with Highbridge Materials Consulting for the laboratory analysis of the historic mortar, stucco, and plaster. It should be noted that the current materials analysis is fairly limited in terms of scope due to budgetary constraints. While it documents in great detail certain mortar, plaster, and stucco materials and contributes to a better general understanding of the fort’s physical evolution over time, it is by no means meant to be an exhaustive study of the fort’s masonry materials and paint finishes. This fort contains numerous unique mortar materials, and this study was only able to analyze a few that are believed to be representative of the most common mortars observed at the fort. Additional study and testing will be required to more fully understand and document the fort’s construction materials. This report, in combination with earlier materials analyses studies, represents a foundation on which this subsequent analysis can build. To guide future studies, this report will make recommendations for additional materials testing and analyses. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 1. Fort Christiansvaern, exterior, south (entrance) elevation. Figure 2. Fort Christiansvaern, interior courtyard, view of the north elevation of the south curtain. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 3. Fort Christiansvaern, exterior, north elevation, view from the bay. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 2.0 BACKGROUND INFORMATION1 Fort Christiansvaern was built for the Danish West India and Guinea Company from 1739-1750. It is a brick and rubble masonry structure currently covered with stucco, located on the shoreline of Christiansted harbor, St. Croix, U. S. Virgin Islands. The fort remains largely an 18th century structure with significant alterations and additions occurring in the 19th century and numerous repair campaigns throughout its history. The following is a brief list of the more significant changes to the fort which are relevant to the materials examined in this study: • 1739-1750 (original period of construction) • 1774-78 (partial reconstruction after a hurricane) • 1817-18 (major rehabilitation including repointing and stucco work) • 1834-35 (major additions/alterations including repointing and stucco work) • 1849-77 (very little work done, time of austerity/declining economy) • 1878 (converted from a fort to use as a police station/courthouse) • 1909-16 (general building rehabilitation) • 1955 (NPS takes over ownership/site management) • 1999 (masonry repairs and limewashing) • 2010 (significant post-hurricane stucco repairs, approximately 35% of fort re-stuccoed) • 2021 (minor stucco repairs, all stucco completely repainted with a silicate paint) BCA reviewed materials and reports as part of this study, primarily the Historic Structures Report, Part 1: Fort Christiansvaern, Christiansted, St. Croix, U.S. Virgin Islands from 1960 and two materials analysis reports from 1983, “Narrative Report on the Findings of Historic Structure Inspection: Conclusions and Recommendations” and “Report on Architectural Finishes at Fort Christiansvaern: The Von Scholten Period: 1827-1848.” The latter two documents have been included with this report, for reference, as Appendix A. 1 The content of this section was derived from Historic Structures Report, Part 1: Fort Christiansvaern, Christiansted, St. Croix, U.S. Virgin Islands. National Park Service, 1960. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 4. Fort Christiansvaern, first floor plan, ca. 1778-1780, by Peter Lotharius Oxholm. (Danish National Archives, Chamber of Revenue, Maps and Drawings Collection, card no. 337.304, cs.sa.dk/picture/view-values/676872?selectedTab=116 &locale=en). BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 5. Fort Christiansvaern, first floor plan, 1836, by First Lieutenant Gjellerup and Second Lieutenant Friis. (Danish National Archives, Chamber of Revenue, Maps and Drawings Collection, card no. 337.109, cs.sa.dk/picture/view-values/676797?selected Tab=116&locale=en) BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 3.0 METHODOLOGY BCA performed a site visit in June 2021 to investigate the fort’s masonry materials (mortars, stuccos, plaster) in situ and remove representative samples. Paint finishes on wood and masonry were also investigated in situ and sampled. BCA removed 15 samples of finishes and 23 samples of mortar, plaster and stucco. Each sample was bagged, labeled with its location, and returned to BCA’s Philadelphia conservation laboratory. All 15 finish samples were analyzed as part of this study, however, only three of the 23 masonry material samples were analyzed due to budget constraints. It should also be noted that BCA’s site investigation and sampling focused on the interior elevations of the fort and not the exterior, as the exterior walls had been recently re- stuccoed and painted. See Appendices B and C for a list of the locations from which all samples were removed, as well as a key to the room names and numbers used by BCA for this study. Each finish sample was embedded in Extec® polyester resin2 and sectioned on a Buehler IsoMet® low-speed saw. The sectioned samples were then dry-polished using a series of fine Micromesh® cloths ranging from 6,000 to 12,000 grit. Sectioned samples were observed under a Nikon Eclipse E200® compound microscope in both visible light passed through a daylight-correction filter and ultraviolet light.3 Photomicrographs of representative samples were taken using a 5.9­ megapixel DS-Fi3® color digital camera system and are included in this report to illustrate specific observations. Photomicrographs and stratigraphy charts for all finish samples are included in Appendix D. Highbridge Materials Consulting, Inc. performed petrographic, chemical, and gravimetric analysis of the masonry material samples using the procedures specified in ASTM C1324 – Standard Test Method for Examination and Analysis of Hardened Masonry Mortar. The results of the analysis are summarized in Section 5.1 and Highbridge’s full report is included in Appendix E. 2 Extec® polyester resin is a commercial polyester/methacrylate resin polymerized with a methyl-ethyl-ketone peroxide catalyst. 3 The ultraviolet light was generated by a mercury illumination system passed through a violet filter cube (EF4 V-2A Ex400/40 Dm 430 Bar 450). BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 4.0 In Situ Observations 4.1 In Situ Observations: Masonry Materials (Mortar, Plaster, Stucco) The masonry materials (mortars, plasters, and stuccos) of the fort were visually examined over the course of a three-day site visit. The focus was on the interior elevations of the fort since the exterior was recently re-stuccoed and painted. The visual investigation allowed for a general understanding of the physical evolution of the various materials simply by looking at their placement (by looking at which material was placed over another, relative dates of installation can be determined), in tandem with archival information such as historic plans of the fort. Because of the large quantity of masonry materials present at the fort, an emphasis was placed on identification and discussion of the earliest existing masonry materials. These early materials were also the subject of the laboratory analysis. Therefore, significantly more information is provided on these materials in this report. Based on this site examination, the masonry materials could be classified into four primary groupings, as discussed below and as depicted in the following photographs. Mortar Type A. Earliest Existing Mortar (possibly ca. 1739-50) (Samples Mortar.4, Mortar.19, Mortar.20, Mortar.21B) This mortar appears to be the earliest mortar at the fort and most likely dates to the original period of construction, 1739-50. It is bright white in color with a slight pinkish hue and appears to have relatively fine aggregate, none of which is particularly visible in hand samples. As discussed in Section 5.2, the mortar is a high calcium lime-based mortar made with natural corraline sand. This mortar was found in brick masonry in multiple locations (inside the slave cells of the south curtain, on the east exterior wall of the south curtain at the second-floor level and in a window opening of the second-floor level of the south curtain). In two of these locations (the slave cell interior and the south curtain window opening), where the brick surface had not been stuccoed over, the mortar joint was tooled to create a convex, rounded bead. It also had evidence of washes applied over top (see discussion of finishes in Section 5.2 below). In addition, the mortar is installed to compensate for irregular brick arrises, with the tooling creating a uniform horizontal line. This decorative treatment was seen on the columns as well as the underside of the arched opening in the slave cells (now enclosed) and the arched window openings of the second-floor gallery of the south curtain. (Figures 6-9) The decorative nature of the joint treatment, as well as the presence of washes over top of the brick masonry, indicate that the brick masonry was originally exposed and intended to be seen. It was not stuccoed originally. How extensive this treatment was on the fort is not clear. The physical evidence observed in this study is unfortunately not sufficient to definitively identify which portions of the fort’s masonry were stuccoed vs. exposed brick masonry. It is possible that the interior-facing walls of the fort were exposed brick while the exterior-facing walls were stuccoed. However, this could not be determined as part of the current study. The 1983 “Narrative Report on the Findings of Historic Structure Inspection: Conclusions and Recommendations” mentions washed brick masonry existing under later applied plasters and stuccos, but it does not discuss the earliest existing mortar identified in this study. Nor does it BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses discuss the original tooling and mortar installation documented in this study, which most likely represent the original masonry appearance (at least on the interior elevations of the fort). Mortar Type B. Second Oldest Mortar/Plaster (possibly ca. 1779) (Samples Mortar.1, Mortar.3, Mortar.14B) This mortar is pale warm yellow with large visible aggregate particles that are typically brown and gray in color. It is also a high calcium lime-based mortar made with corraline sand. It was found as the earliest mortar in Room 12, suggesting this room may have been constructed or significantly altered after the original period of construction since the earliest mortar referenced above was not found in this room. In Room 12, it appears as a parging or possibly a concrete/rubble wall infill. As a mortar, it was also found in the brick walls that were added to the ground floor level of the south curtain, enclosing the once exposed brick columns, and creating the slave cells, as discussed above in the “Mortar Type A. Earliest Existing Mortar” section. These walls are shown on the 1779 floor plan of the fort, so they existed at that time but are not original since they were clearly added after the brick columns, which they enclose. (Figure 4) The mortar also appears to be present on the north wall of Room 24B, which is in the northwest bastion, but on a wall identified as a later added partition wall on the 1959 HABS drawing. (Figures 10-13) This mortar may be the same material described as “light pink stucco” in the 1983 “Narrative Report on the Findings of Historic Structure Inspection: Conclusions and Recommendations”. This stucco, which the author of that report considered historic, was found under a white cementitious plaster in the interior rooms of the fort. Mortar Type C. Third Oldest Mortar/Plaster (possibly ca. 1817-18 or ca. 1834-37) (Samples Mortar.2, Mortar.8, Mortar.9, Mortar.21C, Mortar.22, Mortar.23) This material, which exists as both a mortar and a plaster, was found in multiple locations throughout the fort. It is white in color with distinct black aggregate, occasionally large. While similar in color to the earliest existing mortars, it appears to have more sand and a slight grayish hue. It is also typically quite thick. As discussed in Section 5.2, like the other two mortars, it is a high calcium lime mortar made with coralline sand. Although it is the third oldest mortar observed during BCA’s site visit, it is still relatively early in terms of its placement in relation to other mortar materials. (Figures 14-15) Given its relatively early date of installation as well as its ubiquitousness, it is believed to date to either the 1817-18 or 1834-35 period of alteration to the fort. The former period (1817-18) was known to have included significant repointing and stucco work. However, it was not possible to definitively date this mortar based on the results of the laboratory analysis or field investigation. This material was found as both a mortar and a plaster in Room 12. As a mortar, it was found in the entire east wall, in the infilled window opening at the south end of the west wall and in the existing window opening at the north end of the west wall. As a plaster, it is applied on all walls of Room 12. It extends past the current tongue-and-groove ceiling, indicating it pre-dates the installation of this wood board ceiling. It was also found as a mortar and plaster on the underside of the west stair of the south curtain that leads to the second-floor level. This stair is believed to date to ca. 1834-35 based on the ca. 1836 plan of the fort. (Figure 5) Several finishes and subsequent plaster skim coats were applied over top of it. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses It is also present as both a mortar and a plaster in Rooms 26E and 24A. In Room 24A, it is found in the embrasure opening on the north wall, where iron bars make it difficult to re-stucco, preserving this earlier evidence. This material may be the same as the “soft white” plaster referenced in the 1983 “Narrative Report on the Findings of Historic Structure Inspection: Conclusions and Recommendations”. That report states that the earliest existing stucco found on the exterior walls of the fort was a soft white plaster that existed under a hard white plaster as well as several hard grayish layers. Mortar Type D. Later Mortars, Plaster and Stuccos (Samples Mortar.5, Mortar.6, Mortar.7, Mortar.10, Mortar.11, Mortar.12, Mortar.13, Mortar.14, Mortar.15, Mortar.16, Mortar.17, Mortar.18) The rest of the mortar, plaster and stucco samples are typically more modern or anomalous materials from a wide range of non-original repair campaigns. This study did not focus on the analysis or characterization of these later masonry materials. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figures 6 and 7. Fort Christiansvaern, first floor level, Room 26C. This room contains the earliest existing mortar found at the fort (Type A). It is visible on these columns, which were enclosed by the adjacent masonry walls some time before 1779 according to an historic floor plan of the fort dated 1779. This mortar is likely the earliest mortar at the fort, dating to ca. 1738-39. Note the tooled mortar joints with the convex rounded profile that were obviously intended to be visible. The mortar is also used to fill irregularities in the brick arrises and, when struck, create the appearance of a straight, regular, thin joint. This is also the location of sample Mortar.4, which was subjected to laboratory analysis. Figure 8. A location at the second-floor level where a tooled brick mortar treatment similar to that found in the location shown in Figures 6 and 7 was uncovered behind a removed window frame. Note the red-colored washes applied over the brick and mortar. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 9. Samples Mortar.4 and Mortar.20, which both represent the earliest existing, white-colored mortar found at the fort. Sample Mortar.20 on the right contains evidence of the convex rounded tooling at the surface of the mortar joint (arrow) as well as applied red washes. Figure 10. The warm yellow mortar associated with the second oldest mortar/plaster campaign (Type B). On the west wall of Room 12 shown above, it appears to be applied either as a parging or part of an early concrete/rubble wall infill. This is the location of sample Mortar.1. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figures 11 and 12. The second oldest mortar was also observed on the walls that were added to the ground floor level of the south curtain enclosing the once exposed brick columns (visible in the left photo) and creating the slave cells. In the photograph on the right, sample Mortar.1 removed from Room 12 is shown for comparison. They appear to be the same material. Figure 13. Samples Mortar.1 (left), Mortar.3 (middle) and Mortar.14B (right) represent the second oldest mortar found at the fort (Type B), which is warm yellow in color and contains larger, more visible aggregate than the oldest mortar (Type A). BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 14. The third oldest mortar (Type C), which is also often found as a plaster, can be seen in the right side of this photograph (arrow). It is whitish gray in color and has been used to fill in an older window or door opening on the west wall of Room 12. The mortar in the left side of the photograph is the second oldest mortar (Type B), which is warm yellow in color by contrast. Figure 15. Sample Mortar.2 represents the third oldest mortar, which sometimes also occurs as a plaster. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 4.2 In Situ Observations: Finishes Because of the limited number of finish samples included in this study, it was decided to focus on two aspects of the fort’s paint finishes: the masonry finishes and the paint finishes of Room 12. Understanding the finishes applied to the fort’s masonry surfaces (brick, plaster, stucco) throughout its history is obviously a critical part of documenting the fort’s overall appearance over time and it goes hand-in-hand with the current study of its masonry materials. As for the selection of Room 12 as a focus area, Room 12 is one of the few rooms at the fort that has not been significantly altered and still retains evidence of historic paint finishes, including decorative stenciling on the walls. Therefore, it was seen as a good potential location for historic paint evidence that might be representative of the interior rooms of the fort. Paint samples were removed from both plaster and wood elements of this room. The results of the paint finishes investigation are summarized in Section 5.2 because they are primarily derived from the laboratory analysis of the paint samples. As mentioned before, the exterior walls of the fort were not investigated for historic paint evidence because they had been recently re-stuccoed and painted prior to BCA’s site visit. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 5.0 Laboratory Analysis 5.1 Laboratory Analysis: Masonry Materials (Mortar, Plaster, Stucco) BCA removed 23 masonry material samples from the site for laboratory analysis. Three of the samples were identified as representative of the earliest existing masonry materials at the fort and were selected for laboratory analysis. They were examined petrographically and chemically by Highbridge to determine their composition and condition. The analyzed samples include: • CHRI.Mortar.2: First floor level, Room 12, interior, west wall, brick mortar/plaster. This sample represents the third oldest masonry mortar material observed (Type C), which is believed to date to either 1817-18 or 1834-37. (Figures 16-17) • CHRI.Mortar.3: First floor level, Room 26C, interior, south wall, mortar. This sample represents the second oldest masonry mortar material observed (Type B), which is believed to date to 1779. (Figure 18) • CHRI.Mortar.4: First floor level, Room 26C, interior, east wall, brick mortar. This sample represents the oldest existing masonry mortar material observed (Type A), which is believed to date to 1739-50. (Figures 19-20) The results of the laboratory analysis indicate that all three mortars are generally similar in terms of composition with some variation in sand, most likely due to the fact that the mortars are believed to date to three different construction campaigns. All of the mortars are composed of high-calcium, non-hydraulic lime and well-graded, natural coralline sands. Volcanic grains and other siliceous materials were also noted as minor components of the sand. There is no evidence of any cements or other additives in any of the mortars. Lime-based mortars are typical for the 18th and early 19th centuries, which is consistent with the date of the masonry from which the samples were removed. It is interesting to note that there is evidence in Sample Mortar.3 that the lime was manufactured from fossil coral. Binder to sand ratios for the mortars analyzed were determined to be the following: Mortar.2 (Type C mortar, third oldest mortar observed at fort): 1 part lime: 1.7 parts sand Mortar.3 (Type B mortar, second oldest mortar observed at fort): 1 part lime: 0.9 parts sand Mortar.4 (Type A mortar, oldest mortar observed at fort): 1 part lime: 0.5 parts sand In terms of physical characteristics, Samples Mortar.2 and Mortar.4 are fairly cohesive and hardened, while Sample Mortar.3 is a bit softer and more friable. All three mortars are highly water permeable. Petrographic examination of the mortar samples indicates that they were mostly well-prepared, although Sample Morter.3 appears to have been prepared with more mix water than necessary to yield good workability. This fact is likely responsible for the weaker character of this particular sample. See Appendix E for Highbridge’s full mortar analysis report. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 16. Fort Christiansvaern, first floor level, Room 12, west wall, location of sample CHRI.Mortar.2. Figure 17. Location of CHRI.Mortar.2. This sample represents the third oldest masonry material at the fort, as observed during the current study’s site visit. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 18. Fort Christiansvaern, interior, Room 26C, location of Mortar.3, the second oldest mortar observed at the fort. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses . Figures 19 and 20. Fort Christiansvaern, first floor level, Room 26C, northeast corner. Location of CHRI.Mortar.4, the oldest mortar observed at the fort. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 5.2 Laboratory Analysis: Finishes Masonry Finishes The earliest masonry finishes observed by BCA were washes applied to the brick that was originally exposed on the interior elevations of the fort. The washes were found in two locations of the south curtain where the original brick masonry had not been stuccoed over (inside the slave cells on the ground floor and at the jambs of the window openings of the second-floor level gallery), as well as one location where the brick has been stuccoed over (the east elevation of the south curtain at the second-floor level). As discussed previously in the report, the original brickwork found inside the fort was meant to be exposed and not stuccoed over. It contained a tooled mortar joint that was obviously intended to be seen and not covered. In addition, it is likely that the brickwork was always intended to be painted. Not only do the original bricks appear to be two different colors—brown and yellow—but they also are irregularly shaped with undulating arrises that had to be filled with mortar and tooled to create the illusion of a straight, narrow joint.4 Painting the different colored brick, as well as the decorative mortar treatment, would have provided the appearance of a uniformly colored and neatly installed masonry wall. (Figures 21-26) The earliest finishes applied to the original brick masonry appear to be limewashes, based on their translucent appearance in cross-section. They are matte when viewed in bulk samples and in situ, which is also characteristic of limewashes. The color of the limewash varies by location. The limewash applied over the brick masonry of the slave cells (brick units and mortar alike) is brown in color, similar to the dark brown color of the brick itself. It is also fairly thick, more like a mortar parging or a sanded limewash. The color of the limewash applied over the brick masonry at the second-floor level is dark pink/dark red. It may actually be an even darker red than recorded, as the saturation of the color varies greatly and the removed samples that were used for color matching may not contain the darkest, most saturated version of the limewash color. The dark pink/red limewash was found in two locations on the second-floor level of the south curtain—the window openings of the gallery and the east elevation of the building, which is now stuccoed. The color of the early dark pink/red limewash is the same in both locations. In all three locations, there appears to be only one layer of limewash. It is not clear why two different-colored washes would have been applied to brickwork that presumably dates to the same period. Perhaps it was an intentional differentiation between the masonry of different floor levels or of different uses. It is also possible that the finish evidence may not be complete in these locations and that the washes date to two different periods. It is also unclear when these washes were applied. The 1960 HSR states that the arched openings of the second-floor level of the south curtain were enclosed in 1839, meaning the dark pink/red wash found on the bricks pre-dates this time.5 The prior materials analysis reports and archival information provided to BCA were not particularly helpful in answering the question about when these washes might have been applied and how extensive their application was throughout the fort. The prior studies focus primarily on the color of the exterior masonry walls of the fort and the archival information provided in 4 Although this study did not include an examination of the historic brick unit, it was observed during the course of examining the mortar materials, that the earliest brick appears to be two colors, brown and yellow. In some cases, individual bricks contain both colors, indicating two different colored clays may have been used to make the bricks or possibly the firing of the brick resulted in the bicoloration. 5 HSR, 46. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses these reports as well as the 1960 HSR is not always clear in terms of whether they are referring to interior or exterior wall surfaces. None of the previous reports discuss the limewashed brick that is believed to be an original feature of the fort. It should be noted that there is archival evidence for the use of brown limewashes early in the fort’s history. The 1960 HSR states: “The earliest… accounts indicate that the masonry walls of the fort were stuccoed with lime mortar and limewashed with a combination of yellow ocher and brown red until 1829.”6 It also says the walls were “limewashed with a yellow-brown stone color” in 1839. Whether these descriptions refer to the exterior or interior walls of the fort, or both, is unclear. Perhaps the exterior of the fort was limewashed yellow-ochre while the interior surfaces were limewashed brown-red. These archival references also state that the washes were applied over stucco, which would not have been the case originally for the interior brick masonry surfaces of the fort. The 1960 HSR also states that “the first entry in the accounts for the purchase of red ochre occurs in 1909.”7 However, it seems unlikely that the exposed brick surfaces on the interior of the fort would have been unpainted until 1909 and that the stucco over top of the brick dates to after this time. It is more likely that there is simply no record of an earlier purchase of the pigment used for these brown and dark pink/red washes, and that there were red washes on the interior walls of the fort earlier than previously thought. Clearly, more research is required on this topic, as it could have broader implications for the interpretation of the fort. After these early limewashes, the exposed brick was stuccoed in the slave cells and at the east elevation of the south curtain. At the second-floor level location, the openings were enclosed with wood jalousies. In the slave cells, the plaster was limewashed white and then painted white with a more modern paint. At the east elevation of the south curtain, two layers of stucco have been applied over the brick, a white one and a gray one. The more recent paint finishes include white, dark red and yellow finishes. Other locations of painted masonry were investigated and sampled by BCA. These additional areas include the stucco walls of two embrasures, one in Room 24A on the north wall of the fort and the other in Room 24B on the west wall of the fort. These locations were selected because they retain evidence of red-colored finishes that pre-dated the use of a yellow finish on the fort’s exterior walls. Given the presence of iron bars, these openings are also not able to be accessed from the exterior during exterior repair and repainting projects. In these locations, the red finishes look different from that found on the exposed brick columns discussed above. The samples removed from the west embrasure (Samples F.9 and F.10) have only one layer of dark red finish that appears to be a sanded paint and not a limewash. The sample removed from the north embrasure (Sample F.8) has three different red finishes, each applied over a different stucco. The first and third layers look more like paint while the middle (second) layer looks more like a limewash. None resemble the red or brown washes documented on the brick. The previous materials analysis report from 1983, “Report on the Architectural Finishes at Fort Christiansvaern: The Von Scholten Period: 1827-1848”, dates the red-colored finishes to the 20th century and states they are applied over top of earlier layers of white and yellow limewashes. This is consistent with the information contained in BCA’s samples, although BCA’s samples lacked the earlier white and yellow washes. (Figures 27-28) 6 HSR, 47. 7 HSR, 139 (footnote). BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses BCA also removed samples from the stucco on the interior of the fort in two other locations, the underside of the west stair of the south curtain and the south wall of the ground floor corridor of the south curtain (above the door to Room 12). The stucco under the stairs is constructed of yellow brick with a soft white stucco applied over top. As observed in situ, there are gray washes applied over the stucco followed by red-brown washes. Following this, an additional white-colored stucco (harder than the first) was applied and topped with yellow- brown washes, another then layer of stucco and the current yellow paint. Unfortunately, only the more recent finishes were captured in the cross-section sample (Sample F.14). The gray washes observed on the earliest layer of stucco may relate to the “blue-gray” finish applied to the walls in 1829, according to the 1960 HSR.8 (Figures 29-30) The sample removed from the south wall of the corridor only contains more recent stucco and paint finishes (Sample F.15). (Figure 31) 8 HSR, 47. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 21. In one of the slave cells (Room 26C), the brown wash (red arrow) applied to the bricks is visible under the current white finishes. Note the bicoloration of the bricks, yellow and red brown (black arrows). The original tooled, white-colored mortar joint is also visible in this location. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 22. In the window openings on the second-floor level of the south curtain, the dark pink/red wash applied to the original brickwork is clearly visible. It is a different color, redder, than the wash found on the bricks of the first-floor level (as seen in Figure 21). Figure 23. A photomicrograph of Sample F.11 removed from the painted brick above. It shows both the yellow brick and a small amount of white-colored mortar, as well as a single layer of red limewash (arrow). Visible light, 40x magnification. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 24. A piece of mortar (sample Mortar.20) removed from the jamb of the window opening on the second-floor level of the south curtain (the location on Figure 22 above). Note the red limewashes applied over the mortar, as well as the profile of the mortar in the photograph on the right, showing the curved portion that was installed in the joint in section. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 25. This piece of yellow brick (Sample F.13) was removed from the east exterior wall of the south curtain. It was taken from underneath layers of later stucco and paint finishes. It contains one to two layers of red/red brown washes, similar to that found on the window opening illustrated in Figure 22. Figure 26. Photomicrograph of Sample F.13 showing the reddish-brown washed applied over the yellow brick. Visible light, 40x magnification. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 27. Photomicrograph of Sample F.8. Visible light, 40x magnification. Figure 28. Photomicrograph of Sample F.9. Visible light, 40x magnification. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 29. The location under the west stair where Sample F.14 was removed from. Note the early gray finish that may date to ca. 1829 (arrow). The overall yellow color is due to the light in the space at the time the photograph was taken. Figure 30. Photomicrograph of a portion of Sample F.14, showing an early layer of stucco plus a red- brown wash and then a later stucco. Visible light, 40x magnification. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 31. This is the location where Sample F.15 was removed from. It contains only more contemporary stuccos and paints. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Room 12 Finishes Samples were removed from both plaster and wood elements of Room 12, including the door trim on the exterior (corridor) face of the door into the room. The samples removed from the woodwork outside of the door into Room 12 will be discussed first, since they relate to the preceding discussion of masonry finishes in this area. (Figure 32) Woodwork The exterior face of the wood frame of the door into Room 12 has a rich finish history (F.2). It has been painted approximately 25 times. The first layer, applied directly to the surface of the wood, is a dark gray. After this, it was painted dark green, cream, olive green, dark gray again, and then yellow-brown, olive green or tan approximately 14 times. All of these paint layers appear to be early paints given the coarseness of their pigment particles and overall heterogeneous appearance. After these early paint layers, the wood frame was painted pale gray, khaki, pale green, and dark green. The wood frame of the corridor opening (F.1) has a similar stratigraphy but lacks the earliest paint layers. Its first finish is the yellow brown found as the fourteenth paint layer in sample F.2. Sample F.1 also has evidence of a red material at the surface of the wood, most likely a pore filler used to prepare the wood for painting. It also has many more modern dark green paint layers than sample F.2 (nine versus one). (Figures 33-34) The earliest dark gray finish found on the woodwork of the south curtain first floor passage is consistent with the historic paint evidence discussed in the 1960 HSR and the 1983 materials analysis report. Both documents state that the earliest finish on the fort’s woodwork is dark gray.9 The HSR then goes on to say that subsequent paint colors for the woodwork were light yellow (1829-36) and dark green (1836, 1839). The 1983 paint analysis also lists subsequent paint colors for the fort’s exterior woodwork, many of which are comparable to the ones found in these two samples (e.g., tans and yellow browns). Since the first layer present on the wood frame of the passageway is an early but non-original yellow brown, it would be helpful to know what year this wood element was installed (since it would help to date this layer as well as all layers before it that are present in Sample F.2). The paint history on the interior side of the door into Room 12 is very similar to that on the exterior side. Sample F.3, removed from the wood lintel on the interior (room) face of the door, has the same first two paint layers as found in Sample F.2: dark gray and dark green. After this, the two stratigraphies diverge. The interior woodwork was painted olive green, brown, pale gray, and then various shades of tan, gray and khaki. Its most recent layers are pale green and three layers of dark green. While many of these layers match those found on the exterior woodwork, the sequence is slightly different and there are a few colors present in Sample F.3 that are not in F.2. A sample was also removed from the beaded joist of the second floor, visible behind the current tongue-and-groove ceiling (F.4). The earliest finish is a yellow brown followed by a pale gray. These might be the same as the fourth and fifth layers in Sample F.3. If the date that the current ceiling was established could be determined, it would help to date these finishes. (Figure 35) 9 HSR, 47. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Plaster Two samples were also removed from the plaster walls of Room 12, one from the stencil on the east wall (F.5) and one from the gray dado of the west wall (F.6). The sample removed from the dado, which is covered with a white plaster (the same as Mortar.2), contains only a single layer of dark gray paint. There may have been an earlier iteration of a gray dado, but lower on the wall: there appears to be a thinner band of a paler or more weathered gray lower down on the same wall underneath the current dark gray. (Figure 38-39) The sample removed from the stencil area (F.5) contains a layer of yellow ochre followed by dark gray, which represents the stencil design. These finishes may be pigmented limewash, based on their appearance in cross-section. Although not visible in the cross-section, this portion of the wall also contains a pale pink over top of the stencil campaign. It appears matte in bulk and may be a pigmented limewash. After this, the walls appear to have been limewashed white several times. (Figure 36-37) On site, a narrow band of pale gray (possibly the same as observed at the bottom of the east wall) is visible around the door to the corridor on the north wall. It is underneath the ochre/stencil and pale pink finish layers. (Figure 40) The 1960 HSR does not discuss stenciling on the interior walls of the enclosed rooms of the fort. It states that the majority of the rooms were limewashed white originally, although some rooms were also wallpapered. It does mention that the rooms of the west curtain were limewashed yellow in the 1830s and 1840s.10 Perhaps the ochre-colored limewash found in Room 12 dates to the same period. 10 HSR, 73. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 32. Samples F.1 and F.2 were removed from the wood elements in the passageway outside of the door to Room 12. F.1 from the wood frame on the left and F.2 from the door frame on the right. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 33. A montage of two photomicrographs of Sample F.2, removed from the exterior door frame into Room 12, shows the original dark gray layer on the wood (arrow), as well as numerous later layers that range in color from yellow brown to tan to green. Visible light, 40x magnification. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 34. A montage of two photomicrographs of Sample F.1, removed from the wood frame of the south curtain ground floor passage. The red wood filler is visible at the bottom of the photograph as is the original yellow-brown finish. Note this element’s earliest finish is the same as one of the much later yellow-brown paint layers visible in the photomicrograph of Sample F.2 in Figure 32 above. Visible light, 40x magnification. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 35. The beaded floor joist on the ceiling of Room 12, where Sample F.4 was removed from. The pale gray finish applied to this wood element is clearly visible. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 36. The area of stenciling on the east wall of Room 12, where Sample F.5 was removed from. Figure 37. A photomicrograph of Sample F.5, removed from the area of stenciling. Note yellow ochre colored first layer with black/dark gray stencil design layer on top. These finishes appear to be limewashes. Visible light, 40x magnification. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 38. The gray dado of the west wall of Room 12, the location of Sample F.6. Note the lighter- colored, narrower band of gray at the bottom of the wall (arrow), which appears to be an earlier gray dado treatment for the wall. Figure 39. A photomicrograph of Sample F.6 showing a gray paint (most likely limewash) applied over white plaster. Visible light, 40x magnification. F.6 BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Figure 40. The north wall of Room 12 also has traces of black/dark gray stenciling applied over a yellow ochre finish, which only partially remains. An earlier band of gray paint immediately adjacent to the door opening is also visible (arrow). BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses 6.0 CONCLUSIONS AND RECOMMENDATIONS The current materials analysis was able to uncover and document significant information about the fort’s historic materials, both its mortars and its paint finishes. Although the study was somewhat limited in terms of scope, it nonetheless revealed information about the fort’s earliest appearance and the materials used to create it. The fort contains numerous unique mortar materials and finishes, and this study was only able to analyze select materials believed to be the most representative. Additional study and testing will be required to understand and document the full breadth of the fort’s construction materials. One of the most significant discoveries of the materials analysis was the presence of limewashed brick masonry walls during the earliest years of the fort’s history, at least on the interior elevations (the exterior elevations were not included in this study). This brickwork had a tooled mortar joint and several limewashes ranging from red to brown in color. This evidence indicates that the brick was meant to be exposed and that it pre-dated the application of any stucco. BCA’s research suggests that the exposed, limewashed brick was present from 1734-1779 and may have adorned the interior of the fort until as late as 1839, when the arched openings of the second-floor level of the south curtain were purportedly enclosed, covering one of the locations of the red limewashed brickwork. None of the previous reports on the fort discuss the limewashed brick that appears to be an original feature of the fort. Clearly, more research is required on this topic, as it could have broader implications for the interpretation of the fort. Other early paint finishes were also documented in this report and color matches for significant layers are provided below. In terms of the mortar materials, three distinct but similar early mortars were documented as part of the current materials analysis. The mortar appears to date to the earliest periods of construction for the fort, ca. 1734-1837. They are all non-hydraulic, high calcium lime-based mortars mixed with natural coralline sand; and they are all highly water permeable. Lime-based mortars such as these are typical of the 18th and early 19th centuries, as well as Caribbean masonry structures of the period. The mortars examined are also all in good condition. Recommendations for replication mortar mixes for the three mortar types that were analyzed are included below. Additional study of the fort’s masonry materials beyond what was accomplished in the current study is also recommended. There are numerous stuccos, mortars and plasters present at the fort and this study was only able to focus on a select few. More investigation and analysis to confirm the findings of this report, as well as document the characteristics of later masonry materials would be helpful for gaining a more comprehensive understanding of the fort’s materials and physical evolution over time. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Masonry Materials Because the historic high-calcium, non-hydraulic lime mortars examined as part of this study have performed adequately over their life, a replication mortar mix based on their composition is recommended. Therefore, a high calcium lime putty-based mortar is recommended for masonry repair work in the locations where the samples were removed, as well as other locations in the fort where the same mortar types were observed. As a reminder, here are the three mortar types documented in this report, as well as the sample numbers associated with each type. The locations from which the samples were removed are identified in Appendix C. • Mortar Type A. Earliest Existing Mortar (possibly ca. 1739-50) (Samples Mortar.4, Mortar.19, Mortar.20, Mortar.21B) • Mortar Type B. Second Oldest Mortar/Plaster (possibly ca. 1779) (Samples Mortar.1, Mortar.3, Mortar.14B) • Mortar Type C. Third Oldest Mortar/Plaster (possibly ca. 1817-18 or ca. 1834-37) (Samples Mortar.2, Mortar.8, Mortar.9, Mortar.21C, Mortar.22, Mortar.23) As indicated below, a single mortar mix is recommended, even though there was some variation in terms of sand type and amounts in the three historic mortars. A single mix is being recommended primarily because the ingredients and proportions of the three historic mortars were generally the same (high calcium lime-based mortars with natural coralline sand). In addition, using a single mix proportion for these replication mortars will be more practical for repair work. The original proportions of lime putty to sand (1 : 1.7, 1 : 1.09, 1 : 0.5) have also been modified for the recommended replication mix to be more in line with current industry standards. Recommended Replication Mortar Mix for Mortar Types A, B and C • 1 part high-calcium, slaked lime putty • 2 parts sand, selected to match the color and approximate grain size and gradation of the existing sands of each mortar type while conforming to the requirements of ASTM C144 – Standard Specification for Aggregate for Masonry Mortar. NOTE: Different sands will need to be used to replicate each historic mortar type (Types A, B and C) in order to provide a good visual match to the original. Information on each sand (color, gradation) is provided in Highbridge’s report located in Appendix E. In addition, the extracted sand from each of the three mortars will be provided with this report. All of this information can be used for matching purposes. NOTE: Compared to ASTM C144, the modern standard for masonry sands, the aggregates in Samples Mortar.2 and Mortar.4 comply with the permissible gradation limits, while the aggregate in Sample Mortar.3 is too coarse. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Lime putty mortars require special precautions to ensure the proper installation and long-term durability. Because lime putty mortars take longer to cure and carbonate than lime-cement hybrid or hydraulic lime mortars (full carbonation of non-hydraulic lime can take years), it is important to protect the mortar during its initial cure. In order to ensure a proper cure, we recommend that the following precautions be taken when using lime putty mortars: • Install at least 28 days prior to expected freezing temperatures to prevent the mortar from freezing. This should not be an issue on St. Croix; however, it is important to note. • Do not install during the hottest summer months when mortar may dry out prematurely. • Do not install in areas of perpetual dampness. • Protect from sun, wind, and rain for at least 14 days. • Moisten mortar and allow to dry in regular cycles during the initial cure to allow for carbonation. • Best results will be obtained from a mason who is familiar with lime putty mortars, as their workability and working time differ from that of cement-lime hybrid mortars. The lime putty manufacturer’s precautions and recommended installation procedures should be consulted before beginning work. With any replication mix, samples should be created to evaluate the appearance of the new pointing mortar to ensure it matches the original in terms of overall appearance. BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Finishes The following table documents the colors of select historic finishes observed in this materials analysis. The finishes selected for color matching are those that have some type of significance or relevance for the discussion included in this report. They tend to be finishes on wood, plaster and brick that are associated with the earliest part of the fort’s history. For the color matches included in the following table, it is important that physical color samples for each color be reviewed, as the printed or electronic version of the color swatches included below vary from the actual colors. Any attempt to reproduce these pages, including printing from the electronic version of the report, will distort the color of the provided chip. Only the actual color chip or the color notation should be used for paint replication purposes. Element Location Possible Date Finish Description Color Match Originally Exposed Brick Masonry Wall/Column South Curtain, Ground Floor, Slave Cells ca. 1734-1779 Brown Limewash Munsell 5YR 5/4 B. Moore 1162 Wooden Vista Originally Exposed Brick Masonry Wall South Curtain, Second Floor, East Exterior Wall South Curtain, Second Floor, Gallery, Jamb of Current Window Opening ca. 1734-1779 Dark Pink/Red Limewash Note: Actual color may be more saturated and darker, color of finish varies in samples Munsell 7.5R 5/6 B. Moore 1201 Spiced Apple Cider Wood Door Frame South Curtain, Corridor, Door into Room 12 South Curtain, Room 12, Door to Corridor ca. 1734-1779 Dark Gray Paint Munsell N3.25 B. Moore 2118-20 Toucan Black BUILDING CONSERVATION ASSOCIATES INC. July 2023 Fort Christiansvaern. Christiansted, St. Croix, U.S. Virgin Islands. Materials Analyses Element Location Possible Date Finish Description Color Match Beaded Wood Joist South Curtain, Room 12, Ceiling Unknown, possibly mid 19th c. Yellow Brown Paint Munsell 10YR 6/6-7/6 B. Moore 188 Eye of the Tiger Plaster Wall, Painted Dado South Curtain, Room 12, West Wall 1830s-40s Medium Gray Limewash Munsell N4.75 B. Moore HC-178 Charcoal Slate Plaster Wall, Stencil Design (Background) South Curtain, Room 12, East Wall 1830s-40s Ochre-colored Limewash Munsell 10YR 8/6 B. Moore 180 Beverly Hills Plaster Wall, Stencil Design (Stencil) South Curtain, Room 12, East Wall 1830s-40s Dark Gray Limewash Munsell N3.75 B. Moore CW 685 Ambler Slate BUILDING CONSERVATION ASSOCIATES INC. July 2023 Appendix A. Previous Materials Analyses Reports 1/9 FINAL DRAFT NARRATIVE REPORT ON THE FINDINGS OF HISTORIC STRUCTURE EXAMINATION-, CONCLUSIONS t- - - ­ -S'-* AND RECOMMENDATION^. NAME OF SITE: Fort Christians^em , Commandant’s Quarters, 2nd floor, sout^ielevation, windows 114-122* LOCATION OF SITE: Christiansted, St, Croix, U.S, Virgin Islands, Christiansted National Historic Site INSPECTION OF SITE BY; Benjamin Nistal-Moret, Architecture Technician, NPS/SERO/OCR EXAMINATION REPORT FILED BY; Benjamin Nistal-Moret ji DATE OF INSPECTION: ­ 11 January 1983 TIME OF INSPECTION: 1300 - 1700 hrs, SCOPE OF WORK: Determine historic color finishes for exterior windows EXAMINATION OF FINISHES; All openings of the hall were examined -interior and exteriors- where windows 114-122 are located. The hall is positioned above the sally port . Windows open into the main elevation facing the main entrance. Besides windows 114-122, the following doors, including hardware, were examined: doors 54-56, 58-63, and 65. METHODOLOGY: Selective scrapping, cratering, and polishing prior to sample retrieval ere w conducted in order to determine -under field conditions- paint stratigraphy and possible historic finish. FINISHES’ CONDITIONS: Windows 114-122 were xamined (shutters, jambs, heads, and sills) in- eluding their hardware. It was found that due to extensive stripping, alterations, modifications, and introduction of later window types^ original finishes apparently have been lost. Examination of existing ■A-Wi*,---­ V- • . . _i REPORT ON ARCHITECTURAL FINISHES AT FORT CHRISTIANSVAERN: THE VON SCHOLTEN PERIOD: 1827-1848 * * * The problem under study is the establIshment of a significant relation­ ship between the historic exterior polychromy of Fort Christiansvaern and the highest level of architectural development of the structure, in order to sub­ stantiate a process bywhichit will be possible to approximately regain that finish appearance through a systematic preservation/restoration treatment. 1 The Historic Structure Report for Fort Christiansvaern states Exterior Paints and Finishes.— Numerous bills exist for frequent pointing, stuccoing, and limewashing of the exte­ rior walls of the south curtain and the entire fort. The earliest of these accounts indicate that the masonry walls of the fort were stuccoed with lime mortar and lime- washed with a combination of yellow-ocher and brown-red color until 1825 (47). All woodwork was painted "gray" or "stonecolor" during this era (48). The color of the walls was altered to a blue-gray in 1829 (49). All exterior woodwork was apparently a light yellow color until 1836 and thereafter a dark green color (50). All hardware was painted black. Once again in 1839 the walls were limewashed with a yellow- brown stonecolor, and all exterior woodwork was painted green (51). The practice of limewashing the walls was ap­ parently not begun until early in the 20th century (52). Structuraly, Mr. Herbert Olsen argued in his Foreword (p.iii) that The principal conclusion resulting from this study is that Forth Christianvaern is essentially an 18th century structure with some important additions and alterations from the 19th century era of 1834-1857. No major structural changes or additions have been made to the fort since the latter year 1 Appendix B. Existing Floor Plans with Room Names/Numbers Used by BCA HIP ROOF REMOVED RAVELIN YARD CARRIAGE HOUSE SOUTHEAST SOUTHWEST BASTION BASTION STABLE STABLEYARD EAST CURTAIN COURTYARD WEST CURTAIN PRISON YARD NORTHEAST NORTHWEST DEMOLISHED BASTION BASTION WATER BATTERY LATRINES STAIR RUINS 1/32” =1’-0” PLAN NORTH CONTEXT PLAN SCALE: 1/32” = 1’-0” 1 BAR PARTITIONS ADDED 13 8 PARTITION AROUND CISTERN REMOVED 9 10 11 12 14/15 7 WINDOW OPENING 6 INFILLED AT INTERIOR 16 26B 26C 5 26A 26D 17 PLAN NORTH FIRST-FLOOR PLAN (SOUTH) SCALE: 1/16” = 1’-0” 28 33 PARTITION ADDED PLANTER REMOVED 27 AND PAVED 1/16” =1’-0” 2 1/16” =1’-0” 3 20 2 21 22/23 1 26E 24A BAR PARTITIONS 25 ADDED 24B BAR PARTITIONS ADDED LATER PARTITION REMOVED 24C 18 19 3 4 TILE FLOOR, PLUMBING FIXTURES & STALLS ADDED PLAN NORTH FIRST-FLOOR PLAN (NORTH) SCALE: 1/16” = 1’-0” STABLEYARD PLAN SCALE: 1/16” = 1’-0” 1/16” =1’-0” 4 DEMOLISHED RUINS WOOD GATE WOOD GATE WOOD SCREEN PARTITIONS (TYP.) RAISED PLYWOOD FLOOR ADDED TO ROOM 31A 29 30 31A 31B PLAN NORTH PARTITION REMOVED G H I/K L M 1/16” =1’-0” 5 PLAN NORTH SECOND-FLOOR PLAN (SOUTH) SCALE: 1/16” = 1’-0” SECOND-FLOOR PLAN (NORTH) SCALE: 1/16” = 1’-0” 1/16” =1’-0” 6 N PLAN NORTH Appendix C. List of Sample Locations Fort Christiansvaern List of Sample Locations Removed June 2021 Masonry Materials Mortar.1 First Floor, South Curtain. Room 12, west wall, mortar. Mortar.2 First Floor, South Curtain. Room 12, west wall, plaster. Mortar.3 First Floor, South Curtain. Room 26C, slave cell, east wall, mortar. Mortar.4 First Floor, South Curtain. Room 26C, slave cell, northeast column, mortar. Mortar.5 First Floor, South Curtain. Room 26C, slave cell, northeast column, stucco. Mortar.6 First Floor, South Curtain. Room 26D, slave cell, mortar. Mortar.7 First Floor. Room 6, south wall (area of existing penetrations), mortar. Three mortars present: 7A, 7B, 7C. Mortar.8 First Floor. Room 26E, east wall, mortar. Mortar.9 First Floor. Room 24A, north wall, embrasure, plaster/stucco. Mortar.10 First Floor. Room 24B, west wall, embrasure with iron bars, plaster/stucco. Sample removed from interior. Mortar.11 First Floor. Room 24B, west wall, embrasure with iron bars, plaster/stucco. Sample removed from exterior. Mortar.12 First Floor, Exterior. West wall, stucco. Sample taken from prison yard adjacent to embrasure of samples Mortar.11 and Mortar.12. Mortar.13 First Floor, Exterior. West wall, stucco. Sample taken at rectangular opening in west wall of latrine. Mortar.14 First Floor. Room 24B, north wall. Two samples: plaster (14A) and mortar (14B). Mortar.15 First Floor. Room 16, south wall, mortar/plaster of brick-between-post construction. Mortar.16 First Floor. Kitchen, south wall, mortar. Mortar.17 First Floor. Room E, south return of east window (behind wood frame), stucco. Mortar.18 First Floor. Room E, west return of south window, stucco. Mortar.19 Second Floor, South Curtain. East half of gallery, north wall, window opening, mortar. Mortar.20 Second Floor, South Curtain. East half of gallery, north wall, window opening, mortar. Mortar.21 Second Floor, East Elevation (exterior wall of south curtain). Multiple pieces of sample: brick substrate (21A), mortar (21B), white stucco (21C), gray stucco (21D). Mortar.22 First Floor, South Curtain. Underside of west stair, stucco. Mortar.23 First Floor, South Curtain. Wall surrounding door into Room 12, stucco. Paint Finishes F.1 First Floor, South Curtain. West half of corridor, wood frame of corridor opening. F.2 First Floor, South Curtain. South wall of corridor, door to Room 12, casing. F.3 First Floor, South Curtain. Room 12, north wall, door casing. F.4 First Floor, South Curtain. Room 12, ceiling, underside of second floor joist (beaded), currently covered by tongue-and-groove board ceiling. F.5 First Floor, South Curtain. Room 12, east wall, stencil. F.6 First Floor, South Curtain. Room 12, west wall, dado (currently gray). F.7 First Floor, South Curtain. Room 26C, northeast column, painted brick. F.8 First Floor. Room 24A, north wall, embrasure, plaster/stucco. F.9 First Floor. Room 24B, west wall, embrasure with iron bars, stucco. F.10 First Floor. Room 24B, west wall, embrasure with iron bars, stucco. F.11 Second Floor, South Curtain. East half of gallery, north wall, window opening, painted brick. F.12 Second Floor, South Curtain. East half of gallery, north wall, window opening, painted brick/mortar. F.13 Second Floor, East Elevation (exterior wall of south curtain). Painted brick under later stucco. F.14 First Floor, South Curtain. Underside of west stair, stucco. F.15 First Floor, South Curtain. Wall surrounding door into Room 12, stucco. Appendix D. Photomicrographs and Stratigraphy Charts of Finish Samples Visible light, 40x UV light, 40x SAMPLE NO: F.1 LOCATION: First Floor, South Curtain. West half of corridor, wood frame of corridor opening. LAYER COLOR NOTES Substrate wood red-orange pigment/stain in pores of wood 1 pale brown 2 gray 3 yellow brown 4 gray 5 pale gray/white 6 khaki 7 pale green 8 dark green 9 dark green 10 blue- green 11 dark green 12 dark green 13 green 14 white spackle? plaster? 15 dark green 16 dark green Visible light, 40x UV light, 40x SAMPLE NO: F.2 LOCATION: First Floor, South Curtain. South wall of corridor, door to Room 12, casing. LAYER COLOR NOTES Substrate wood 1 dark gray 2 dark green 3 cream 4 dark gray 5 white 6 olive green 7 yellow brown 8 olive-green 9 brown 10 tan 11 tan 12 tan 13 tan 14 tan 15 tan 16 tan 17 khaki 18 tan 19 tan 20 light gray 21 khaki 22 light green 23 dark green Visible light, 40x UV light, 40x SAMPLE NO: F.3 LOCATION: First Floor, South Curtain. Room 12, north wall, door casing. LAYER COLOR NOTES Substrate wood 1 dark gray 2 dark green 3 olive green 4 brown 5 cream 6 brown 7 khaki 8 pale gray 9 cream 10 white 11 light green 12 dark green 13 dark green 14 dark green Visible light, 40x UV light, 40x SAMPLE NO: F.4 LOCATION: First Floor, South Curtain. Room 12, ceiling, underside of second floor joist (beaded), currently covered by tongue-and-groove board ceiling. LAYER COLOR NOTES Substrate wood 1 yellow brown not visible in photo 2 pale gray not visible in photo Visible light, 40x UV light, 40x SAMPLE NO: F.5 LOCATION: First Floor, South Curtain. Room 12, east wall, stencil. LAYER COLOR NOTES Substrate plaster 1 ochre limewash? stencil background 2 dark gray/black limewash? stencil pattern Visible light, 40x UV light, 40x SAMPLE NO: F.6 LOCATION: First Floor, South Curtain. Room 12, west wall, dado (currently gray). LAYER COLOR NOTES Substrate plaster 1 dark gray limewash? Visible light, 40x UV light, 40x SAMPLE NO: F.7 LOCATION: First Floor, South Curtain. Room 26C, northeast column, painted brick. LAYER COLOR NOTES Substrate brick 1 brown limewash 2 brown limewash Visible light, 40x UV light, 40x SAMPLE NO: F.8 LOCATION: First Floor. Room 24A, north wall, embrasure, plaster/stucco. LAYER COLOR NOTES Substrate plaster/stucco 1 white 2 red limewash? 3 white 4 red limewash? 5 white 6 red Visible light, 40x UV light, 40x SAMPLE NO: F.9 LOCATION: First Floor. Room 24B, west wall, embrasure with iron bars, stucco. LAYER COLOR NOTES Substrate stucco 1 red Visible light, 40x UV light, 40x SAMPLE NO: F.10 LOCATION: First Floor. Room 24B, west wall, embrasure with iron bars, stucco. LAYER COLOR NOTES Substrate stucco 1 red Visible light, 40x UV light, 40x SAMPLE NO: F.11 LOCATION: Second Floor, South Curtain. East half of gallery, north wall, window opening, painted brick. LAYER COLOR NOTES Substrate brick/mortar 1 red/pink limewash 2 white mortar 3 red/pink limewash Visible light, 40x UV light, 40x SAMPLE NO: F.12 LOCATION: Second Floor, South Curtain. East half of gallery, north wall, window opening, painted brick/mortar. Early layers only. LAYER COLOR NOTES Substrate brick 1 red/dark pink limewash Visible light, 40x UV light, 40x SAMPLE NO: F.13 LOCATION: Second Floor, East Elevation (exterior wall of south curtain). Painted brick under later stucco. LAYER COLOR NOTES Substrate brick 1 red/dark pink limewash Visible light, 40x UV light, 40x SAMPLE NO: F.14 LOCATION: First Floor, South Curtain. Underside of west stair, stucco. Early layers only. LAYER COLOR NOTES Substrate stucco 1 white limewash? 2 ochre yellow limewash? 3 white stucco Visible light, 40x UV light, 40x SAMPLE NO: F.15 LOCATION: First Floor, South Curtain. Wall surrounding door into Room 12, stucco. LAYER COLOR NOTES Substrate stucco 1 dark gray 2 yellow Appendix E. Mortar Analysis Report (Highbridge Materials Consulting) Mortar Analysis Report Fort Christiansvaern National Historic Site Christiansted, Saint Croix, U.S. Virgin Islands Prepared for Building Conservation Associates, Inc. Client ID BUIL005 Report No. SL1673-01R.1 Original Report Date 10/18/22 Revision Date 06/19/23 404 Irvington Street, Pleasantville, NY 10570 | 914-502-0100 | www.highbridgematerials.com Confidentiality This report presents the results of laboratory testing requested by the client to satisfy specific project requirements. As such, the client has the right to use this report as necessary in any commercial matters related to the referenced project. Any reproduction of this report must be done in full. In offering a more thorough analysis, it may have been necessary for Highbridge to describe proprietary laboratory methods or present opinions, concepts, or original research that represent the intellectual property of Highbridge Materials Consulting and its successors. These intellectual property rights are not transferred in part or in full to any other party. Presentation of any or all of the data or interpretations for purposes other than those necessary to satisfy the goals of the investigation are not permitted without the express written consent of the author. The findings may not be used for purposes outside those originally intended. Unauthorized uses include but are not limited to internet or electronic presentation for marketing purposes, presentation of findings at professional venues, or submission of scholarly articles. Standard of Care Highbridge has performed its services in conformance with the care and skill ordinarily exercised by reputable members of the profession practicing under similar conditions at the same time. No other warranty of any kind, expressed or implied, in fact or by law, is made or intended. Interpretations and results are based strictly on samples provided and/or examined. Cover Image Photograph of Fort Christiansvaern, entrance at the east elevation. Image courtesy of Ms. Dorothy Krotzer of Building Conservation Associates, Inc. Revision History This revision supersedes Highbridge Report SL1816-01. The client has requested that two typographical errors in the figure captions be amended for this revised report. No substantive changes have been made to the text. Respectfully submitted, John J. Walsh President/ Senior Petrographer Heather Hartshorn Chemist/ Staff Scientist Highbridge Materials Consulting, Inc. Highbridge Materials Consulting, Inc. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 1. Executive Summary Three mortar samples are examined petrographically and chemically for this report. The samples are reported to have been taken from masonry walls at Fort Christiansvaern, Saint Croix, U.S. Virgin Islands. The mixtures are generally similar though there are variations in sand compositions and gradations. This could indicate that the samples represent different construction eras. However, there are no materials present that would not have been available during the original eighteenth century construction. All three mortars have a grainy to slightly pebbly texture and a light, warm-toned color. Samples M2 and M4 have a moderately soft binder paste but an overall cohesive and fairly indurate quality. Sample M3 is softer and more friable. All are highly water-permeable. The samples are identified as nonhydraulic lime mortars. There is evidence in Sample M3 to suggest that the lime was manufactured from fossil coral. All are high-calcium products. The mortars contain clean and well-graded natural coralline sands. Binder to sand ratios are estimated at 1 : 1.7 for Sample M2, 1 : 0.9 for M3, and 1 : 0.5 for Sample M4. The materials were mostly well-prepared though the mortar represented by Sample M3 is estimated to have been prepared with more mix water than necessary to yield good workability. This is likely responsible for the weaker character of this one sample. All mortars are fully carbonated as expected for the long service life. The only other secondary chemical effects noted are present in Sample M4. This includes a thin carbonate scale below an overlying lime wash, and drusy chloride (?) salts within pores. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 2. Introduction Between August 27, and September 17, 2021, Highbridge received three mortar/stucco samples reported to have been sampled from Fort Christiansvaern in Saint Croix, U.S. Virgin Islands. The fort was constructed between 1738 and 1749 with significant repair and reconstruction occurring through to the present day. A summary of the received samples and descriptions provided by the client are given in Table 2.1. Highbridge has chosen a shorthand for the sample identifications as indicated in the table, and these are used throughout the remainder of the report. Table 2.1: Summary of Samples Received Client ID HMC ID Client description CHRI.Mortar.1 M1 First floor level, "Room 12", interior, west wall, mortar/parging/plaster. Earliest existing mortar on this wall. CHRI.Mortar.2 M2 First floor level, "Room 12", interior, west wall, brick mortar/plaster. Applied over CHRI.Mortar.1 and also found on several alterations to this room. CHRI.Mortar.3 CHRI.Mortar.4 M3 M4 Removed from a brick wall that appears to have been constructed before 1799, based on a review of historic building plans. The sample is believed to be the same as CHRI.Mortar.1. First floor level, "Room 26C", interior, east wall, brick mortar. Sample was removed from a brick column that was enclosed by 1799 (based on a review of historic building plans), indicating this area may represent a preserved, intact area of brick masonry dating from 1738-99. The mortar/stucco applied directly over this brick mortar is the same as CHRI.Mortar.1. At the client's request, a compositional analysis is performed on three of the four samples (all but Sample M1). The testing includes a petrographic examination and chemical analysis to identify constituents, estimate proportions, and assess overall condition. Acid digestions to extract sand samples for description and gradation are also included. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 3. Methods of Examination The petrographic examination is conducted in accordance with the standard practices contained within ASTM C1324-20a. Data collection is performed or supervised by a degreed geologist who by nature of their education is qualified to operate the analytical equipment employed. Analysis and interpretation are performed or directed by a supervising petrographer who satisfies the qualifications as specified in Section 4 of ASTM C856/C856M-20. Chemical analysis is performed in general accordance with the procedures outlined in ASTM C1324-20a. Water, carbon dioxide, and aggregate weight percentages are determined gravimetrically. Oxide weight percentages are determined by inductively coupled plasma - optical emission spectroscopy (ICP-OES). While ASTM classifies C1324 as a test method, it is intended to serve as a guideline for qualified practitioners with ample experience in the various materials under consideration. Section 10.2 indicates the need for discretion on the part of the laboratory to ensure that methods are tailored to specific mortar compositions. As such, Highbridge chooses specific digestion methods, supplementary tests, instrumentation protocols, and mathematical models to best characterize each individual mortar under consideration. Many of these are proprietary methods that have been researched internally. The following personnel contributed to the examination: Technician: A. Ledwitch Scientific Assistant: J. Negron Staff Scientist: L. Rocha Chemists: H. Hartshorn M. Sinclair Petrographer: J. Walsh Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 4. Laboratory Findings and Discussion 4.1 - Materials All three samples provided for examination have a light, warm-toned color and a somewhat grainy texture. The texture is notably coarser in Sample M3. The colors vary somewhat as summarized in Table 4.1a. The paste is soft in Sample M3 and the matrix appears a bit crumbly. The binder matrix is moderately soft in Samples M2 and M4 but these samples appear more cohesive. All mortars are permeable. Table 4.1a: Mortar Color Sample ID Color Munsell code M2 Yellowish-white 2.5Y 8.75/1.25 M3 Very pale orange 10YR 8.5/2.5 M4 Very light buff 10YR 9/1.5 All three samples contain clean coralline sands that are generally similar in composition. Minor differences between the samples are highlighted in Table 4.1b. Much of the sand consists of the eroded skeletal remains of reef-building organisms and associated invertebrates. The biological fragments include those derived from algae, corals, and snails for the most part. Rock particles are also found in variable concentration. These include sand-sized grains of biomicritc limestone. Volcanic grains and other siliceous materials are also trace to minor components. Clay coatings or friable materials are negligible if not entirely absent. The organic remains often have an open porosity but particles these clearly have good mechanical strength. Sand samples were extracted from all three mortars. The aggregates are mostly uniform with a semi-opaque visual character. Average colors are light buff with some minor to moderate color variegation in the coarser grains, particularly in Sample M3. The aggregate is soft-textured with grain shapes that are mostly subrounded and equidimensional. Gradation analyses were performed on all three sand samples and these results are presented in Section 6. Samples M2 and M4 with only traces of siliceous grain types have nominal top sizes at the No. 8 sieve and peak abundances near the No. 30 sieve. Sample M3 contains a higher quantity of volcanic particles. As most of these are coarser-grained, the nominal top size is found at the 3/8" sieve for this sample. The peak abundance for this sand is between the No. 16 and N0. 30 sieves. Though some minor amount of crystalline calcite fines is observed petrographically for all three samples, there is no significant clay or unwashed fine debris associated with the aggregate of any sample. Compared to ASTM C144, the modern standard for masonry sands, the aggregates in Samples M2 and M4 would comply with the permissible gradation limits while the aggregate in Sample M3 would be too coarse. Of course, these comments are only made for comparative purposes. The modern standard does not necessarily apply to historical lime-based mortars. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 4.1b: Differences in Sand Appearance and Composition This table presents a summary of some more notable differences in the sand composition present in the three mortar samples. More complete descriptions of the sand components are provided in Tables 5.1 through 5.3. Sample ID Munsell color (average) Biological forms Biomicrite grains Siliceous grains M2 10YR 7.75/1.25 Halimeda dominant Minor Trace quartz and volcanics M3 9YR 7/2 Coral dominant Abundant Minor feldspathic volcanics M4 10YR 8/1.75 Biodiverse, coral with both aragonite and Abundant Trace polycrystalline quartz calcite The binder in all three samples is a high-calcium, nonhydraulic lime. No cementitious materials or pozzolans are identified in any of the mixtures. The cured lime pastes have a high capillary porosity and this is typical of lime-based mortars. The microporosity is very high in Sample M3. The mortars lack the microscopic shrinkage cracks that are often observed in pure lime mixes. The hardened binders all have uniform microtextures though the paste in Sample M3 has a notable grainy character at the microscopic scale. The chemical analysis was used to estimate the lime compositions and these results are presented in Table 7.4. Though the lime could have been prepared from the same source material, there is too much variation in the minor impurities to be able to make this determination. All are clearly high-calcium varieties with too few siliceous and aluminous impurities to have produced any meaningful hydraulicity. On a pre-slaked basis, the lime in Samples M2 and M4 have CaO contents greater than 95%. The measured CaO in Sample M3 is a little lower at 91%. However, it is suspected that some of the more soluble components of the volcanic aggregate have mobilized in service. The lime was quite well dispersed and the putty may even have been screened before use. Discrete lime particles are fairly uncommon in all samples and most are nondescript. However, there are a few grains identified petrographically in Sample M3 that contain pore structures similar to those observed in the skeletons of scleractinian corals. It seems likely for this mortar that fossil coral was used to produce the lime. This may have also been true of the other samples though only one other scarce piece of petrographic evidence was observed in Sample M4. 4.2 - Component Proportions The component proportions are estimated from the chemical analysis presented in Section 7. As summarized in Table 4.2a, the sand contents are lower than would be expected in a modern masonry mortar. However, pure lime mortars with lime to sand proportions of about 1 : 1 on average were typical in Colonial Era mortars of the Americas. Mixes with lower sand contents can be volume-stable and even more durable than sandier mixtures provided mix water contents are controlled. Table 4.2a: Summary of Mixture Proportions The ratios reported here calculate the lime in the form of a putty rather than a dry hydrate. Sample ID Lime : sand ratio M2 1 : 1.7 M3 1 : 0.9 M4 1 : 0.5 Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 4.3 - Condition and Service Performance Based on the examined sample pieces, the constituents were well-blended in all three mortars. No streaks or clots of lime or sand are identified. In fact, undispersed lime particles are rarely coarser than 1 millimeter and there are relatively few of these overall. This suggests that the lime may have been screened before use. All mortars are compact and well- consolidated. The only evidence for a workmanship deficiency is in the particularly high capillary porosity and somewhat friable and crumbly matrix of Sample M3. This suggests a higher mix water content than necessary to produce a workable mix. Still, the qualities of the hardened product are not outside those typically observed in historical high-calcium lime mortars. Mix water contents are estimated to have been more appropriate in the other two samples. The more cohesive and somewhat indurate quality of these two mortars can probably be attributed to lower mix water contents. These two mortars were likely fatty though stiff when freshly-prepared. The sand gradations also likely contributed to greater cohesive strength where mix water contents were not excessive. All else being equal, mortars with coarser sand are stronger than those with finer sand. Regardless of any strength variation, all three mortars are highly water-permeable as expected for the design. The lime paste is fully carbonated in all examined samples and this is a normal and desirable consequence of long-term curing. No microcracking is identified petrographically and there is no physical distress observed in any sample. Though there is some microscopic granularity in the carbonated lime of Sample M3, none of the lime paste is chemically altered or decomposed. Secondary salt deposits are only identified in Sample M4 and none have been observed to have caused any physical damage. These include thin carbonate scale deposits between the original tooled face and one to two layers of lime wash. There are also fine salt deposits within pores and at the rear surfaces of some of the sample pieces. The optical isotropism, low relief, and occasional cubic character suggests a chloride salt. However, no further instrumental analysis was performed to confirm this identification. It should be noted that the lack of observed soluble salts in the other two samples is not necessarily an indication that they are absent. It is always possible for salt to be present in submicroscopic capillaries but not visible at the scale of the light microscope. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 5. Petrographic Data Table 5.1: Petrographic Data - Sample CHRI.Mortar.2 Sample ID Chri.MORTAR.2 As-received description Description The sample consists of several small to medium mortar fragments and a moderate abundance of granules and powder. The shapes of the larger pieces are mostly angular and irregular. The thickest piece is about 1". The total sample weighs 81 grams. Surfaces All surfaces are compact. No tooling or bed surfaces are obvious. However, there are several fresh, unsoiled, planar surfaces with a somewhat rough sandy texture that could represent masonry contacts. Hardness/friability The paste is soft to moderately soft. However, the mortar is indurate and nonfriable. Appearance Fresh surfaces have a dull luster and a yellowish-white color (Munsell code approximately 2.5Y 8.75/1.25). Absorptivity The mortar matrix is very rapidly water-absorptive. Other details No cracks or secondary mineralizations are visible in hand sample. White binder grains are very rare and are less than 1 millimeter in size. Sand Lithology The aggregate is primarily a coralline sand consisting of the eroded skeletal remains of reef-building organisms and associated marine invertebrates. The biological forms that have contributed to the aggregate include green algae (Halimeda), scleractinian coral, red algae, gastropods (snails), foraminifera, and echinoid spines. The latter two are minor. A minor amount of bioclastic limestone intraclasts are also observed. The major forms tend to be variably porous though all appear to be mechanically robust. There are also traces of quartz and undifferentiated volcanic particles. Appearance The sand is mostly uniform and opaque to semi-opaque. The overall color is light buff (Munsell color code approximately 10YR 7.75/1.25). Minor darker gray and reddish particles in the +No. 30 fraction provide some color variegation. Gradation The sand is medium-grained and broadly graded. The nominal top size is at the No. 8 sieve, the peak abundance near the No. 30 sieve, and the fines content is negligible. Shape/aspect ratio Sand shapes are subrounded on average. Aspect ratios are mostly equidimensional to subequant. There is some variability in grain texture due to the high diversity of fossil forms. Clay coatings/friable materials No significant clay coatings or friable materials are evident. Other None Binder matrix Paste uniformity The lime paste is uniformly-developed. Capillary porosity High Microscopic shrinkage cracking None significant Residual calcium hydroxide Depleted due to complete carbonation Evidence for admixtures1 None Binder residuals Binder type High-calcium, nonhydraulic lime Hydraulic cement None identified Lime Undispersed lime grains are found in very low abundance as fine-grained particles that are internally nondescript and fully carbonated. Grains are always less than 1 millimeter in diameter. Pozzolans/SCMs2 None detected Other Very fine-grained bits of wood cinder ash are found in exceedingly trace abundance throughout the lime paste. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 5.1 (cont'd.): Petrographic Data - Sample CHRI.Mortar.2 Sample ID Chri.MORTAR.2 Pigment Concentration None detected Composition n/a Particle size n/a Color of extracted pigment n/a Other materials Details None Placement features Constituent distribution The mortar constituents are well-dispersed. Mix water There is no variation in paste density that would suggest inconsistent distribution of mix water. Compaction/consolidation The mortar is compact and well consolidated. Estimated air content/structure The air content is estimated at less than 2% by volume. Voids are mostly spherical and very fine in diameter. Paste-sand interfaces Sand grains are well-coated with binder. Other None Secondary effects Carbonation The lime paste is fully carbonated throughout the thickness of the sample pieces provided. Paste alteration None detected Cracking None significant Mineral deposits None detected Surface erosion/weathering No obvious joint surfaces are included with the sample. Other None Notes: 1. Organic admixtures or soluble inorganic additives cannot be detected petrographically, though their effects on paste microstructure can sometimes be discerned. 2. SCMs = supplementary cementitious materials. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 5.2: Petrographic Data - Sample CHRI.Mortar.3 Sample ID Chri.MORTAR.3 As-received description Description The sample consists of a mixture of small fragments, granules, and powder. Larger pieces have a lumpy texture due to the differential loss of paste around coarse sand grains. The sample weighs a total of 31 grams. Surfaces All surfaces are compact. No tooling or bed surfaces are obvious. There are also no weathered faces and all mortar appears fresh. Hardness/friability The paste is soft. The mortar can be handled gently though feels like it would crumble easily(possibly due to weak paste-aggregate interfaces). The mortar was not aggressively probed due to the limited sample size. Appearance Fresh surfaces have a dull luster and a very pale orange color (Munsell code approximately 10YR 8.5/2.5). Absorptivity The mortar matrix is very rapidly water-absorptive. Other details Cracking is not assessed due to the small sample size. No secondary mineralizations are visible. Only one white binder particle was noted visually at the millimeter-scale. Coarser sand is evident in hand sample including one pebble-sized orange volcanic particle. Sand Lithology The aggregate is primarily a coralline sand consisting of the eroded skeletal remains of reef-building organisms and associated marine invertebrates. The biological forms that have contributed to the aggregate mostly include scleractinian coral and gastropods (snails). A fairly significant component of the sand also includes grains of biomicritic limestone. Minor biological debris in the sand includes fragments of echinoids spines, green algae (Halimeda), red algae, and foraminifera. In addition to the coralline sand, there is a minor component of volcanic grains. These are generally feldspathic with a high content of undifferentiated groundmass and an absence of ferromagnesian phenocrysts. This, despite some heavy iron alteration in some grains. The volcanic grains tend to be found in the coarser grain sizes. Appearance The sand is uniform in the finer grain sizes but displays moderate color variegation in the coarser particles. The grains are opaque to semi-opaque. The overall color is buff (Munsell code approximately 9YR 7/2). The coarser particles have a variety of colors including rusts, reds, darker grays, and lighter greenish grays. Gradation The sand is coarse-grained and broadly graded. The nominal top size is at the 3/8" sieve, the peak abundance between the No. 16 and No. 30 sieves, and the fines content is negligible. Shape/aspect ratio Sand shapes are subrounded on average. Aspect ratios are mostly equidimensional to subequant. There is some variability in grain texture due to the high diversity of fossil forms. Clay coatings/friable materials No significant clay coatings or friable materials are evident. Porous clay lumps are present but very minor. These have mineral inclusions that associated these with the volcanic component of the aggregate. Other None Binder matrix Paste uniformity The lime paste is uniformly-developed. However, the cured binder is noticeably grainy in texture at the micron scale. Capillary porosity Very high Microscopic shrinkage cracking None significant Residual calcium hydroxide Depleted due to complete carbonation Evidence for admixtures1 None Binder residuals Binder type High-calcium, nonhydraulic lime. Soluble impurities measured chemically may or may not be associated with the lime. Hydraulic cement None identified Lime Undispersed lime grains are found in moderately low abundance as fine-grained particles that are generally less than 1 millimeter in diameter and fully carbonated. Many of the grains are internally nondescript though some have the microgranular texture of the adjacent lime paste. More importantly, several lime grains contain internal pores that coincide with those found in scleractinian corals. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 5.2 (cont'd.): Petrographic Data - Sample CHRI.Mortar.3 Sample ID Chri.MORTAR.3 Binder residuals (cont'd.) Pozzolans/SCMs2 None detected Other Very fine-grained bits of wood cinder ash are found in exceedingly trace abundance throughout the lime paste. Pigment Concentration None detected Composition n/a Particle size n/a Color of extracted pigment n/a Other materials Details None Placement features Constituent distribution The mortar constituents are well-dispersed. Mix water There is no variation in paste density that would suggest inconsistent distribution of mix water. Compaction/consolidation The mortar is compact and well consolidated. Estimated air content/structure The air content is estimated at about 2% to 3% by volume. Voids are mostly subspherical and fine in diameter. Paste-sand interfaces Sand grains are well-coated with binder. Other None Secondary effects Carbonation The lime paste is fully carbonated throughout the thickness of the sample pieces provided. Paste alteration None detected Cracking None significant Mineral deposits None detected Surface erosion/weathering No obvious joint surfaces are included with the sample. Other None Notes: 1. Organic admixtures or soluble inorganic additives cannot be detected petrographically, though their effects on paste microstructure can sometimes be discerned. 2. SCMs = supplementary cementitious materials. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 5.3: Petrographic Data - Sample CHRI.Mortar.4 Sample ID Chri.MORTAR.4 As-received description Description The sample consists of several small joint mortar fragments along with a moderate abundance of pebble-sized pieces and minor loose granules and powder. The sample weighs a total of 31 grams. Joint heights are approximately 3/4" though possibly as much as 1". Depths are represented up to about 3/8". Surfaces The tooling has a grapevine profile with a 1/4" wide convex bead flanked by roughly planar surfaces flush with the top of the bead. There are some reddish stains on surfaces that are presumed to have been in contact with the masonry. These surfaces slope/taper inward from the joint face and the stains are possibly brick residues. The rear surfaces of the mortar samples appear to be fresh breaks although some of the surfaces are a little rounded and soft-textured. Hardness/friability The paste is soft to moderately soft. The mortar was not aggressively probed to avoid disaggregating the limited sample. Visually, the mortar appears moderately cohesive and nonfriable. Appearance Fresh surfaces have a dull luster. The freshest area has a very light buff color (Munsell code approximately 10YR 9/1.5) but most parts of the mortar are a bit more yellowed. Absorptivity The mortar matrix is very rapidly water-absorptive. Other details The sample pieces are small but there is no obvious cracking visible. One sample piece has a sugary semi- translucent scale deposit along the tooled face. Other sample pieces have tooled faces that are covered in an opaque white powdery coating with a slightly satiny luster. A couple of white lime grains are visible in hand sample at several millimeters in diameter. Sand Lithology The aggregate is primarily a coralline sand consisting of the eroded skeletal remains of reef-building organisms and associated marine invertebrates. The biological forms that have contributed most to the aggregate include green algae (Halimeda), gastropods (snails), and scleractinian coral. The corals exhibit one of two types of internal texture. Some contain original aragonite while others have recrystallized to an ultrafine-grained equigranular calcite. Other organisms observed in minor to trace quantity include red algae and foraminifera. Also fairly abundant in the sand are grains of biomicritic limestone. Finally, there are also traces of siliceous grains. Most of these consist of very fine-grained polycrystalline quartz. Appearance The sand is uniform and opaque to semi-opaque. The overall color is light buff (Munsell color code approximately 10YR 8/1.75). There are minor darker gray grains that provide some color variegation in most of the grain sizes. These are more visible above the No. 30 sieve. Gradation The sand is medium-grained and broadly graded. The nominal top size is at the No. 8 sieve, the peak abundance near the No. 30 sieve, and the fines content is negligible. Shape/aspect ratio Sand shapes are subrounded on average. Aspect ratios are mostly equidimensional to subequant. There is some variability in grain texture due to the high diversity of fossil forms. Clay coatings/friable materials No significant clay coatings or friable materials are evident. Other None Binder matrix Paste uniformity The lime paste is uniformly-developed. However, the cured binder is slightly grainy in texture at the micron scale. Capillary porosity High Microscopic shrinkage cracking None significant Residual calcium hydroxide Depleted due to complete carbonation Evidence for admixtures1 None Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 5.3 (cont'd.): Petrographic Data - Sample CHRI.Mortar.4 Sample ID Chri.MORTAR.4 Binder residuals (cont'd.) Binder type High-calcium, nonhydraulic lime Hydraulic cement None identified Lime Undispersed lime grains are found in very low abundance as fine-grained particles that are fully carbonated and usually about 1 millimeter in diameter give or take. Most are internally nondescript though the carbonated lime within lime grains is often sparser and more microgranular than the adjacent lime paste. A single grain is detected that has an internal texture similar to that of a coral. However, the evidence is not especially convincing. Pozzolans/SCMs2 None detected Other None Pigment Concentration None detected Composition n/a Particle size n/a Color of extracted pigment n/a Other materials Details One to two coats of a thin lime wash coat most of the tooled surfaces. The wash has a maximum thickness of about 0.5 millimeters. Placement features Constituent distribution The mortar constituents are well-dispersed. Mix water There is no variation in paste density that would suggest inconsistent distribution of mix water. Compaction/consolidation The mortar is compact and well consolidated. Estimated air content/structure The air content is estimated at less than 2% by volume. Voids are mostly irregular and very fine in diameter. Paste-sand interfaces Sand grains are well-coated with binder. Other None Secondary effects Carbonation The lime paste is fully carbonated throughout the thickness of the sample pieces provided. Paste alteration None detected Cracking None significant Mineral deposits Calcium carbonate scale deposits are common along the joint surfaces. These are present as thin veneers below the lime wash when this is present. Cubic, isotropic salt deposits consistent with chloride salts are present within pores and along the rear surfaces of some of the sample pieces. The identification of these was not confirmed chemically or through x-ray diffraction analysis. Surface erosion/weathering Though there are carbonate deposits along the joint faces, there is no weathering or erosion. Other None Notes: 1. Organic admixtures or soluble inorganic additives cannot be detected petrographically, though their effects on paste microstructure can sometimes be discerned. 2. SCMs = supplementary cementitious materials. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 6. Aggregate Sieve Analysis For each mortar sample, a single subsample was used to produce the chemistry aliquot and the extracted sand sample. The following procedure was used: • A representative sample was taken and weighed analytically to represent the complete yield. • These subsamples were disaggregated and macerated in hot water to loosen the binder fraction from the aggregate. The disaggregated samples were stirred to suspend the binder. The suspended binder was decanted into a separate beaker. The original sample was repeatedly rinsed and decanted until the water ran clear. • The process yielded two subsamples in water. One is a finer-grained suspension of cured lime paste potentially with some minor silt derived from the aggregate. The other subsample consists of sand in which much but not all of the lime paste had been removed. Both beakers were placed in a low-temperature oven and evaporated to dryness. The lime binder sample was used for chemical analysis while the sand sample was used to extract the aggregate and help normalize the chemical weight percentages. • The sand samples were each digested for several seconds in an acetic acid solution buffered at a pH of 4.5. The samples were flooded with water to arrest the reaction. The sample was dried and examined under a stereoscopic microscope to determine whether any remaining lime paste was sufficiently decomposed and rinsed away. It was necessary to repeat the mild acid digestion, rinsing, and drying several times for each of the samples. • Once the sand was almost completely clean, the aggregate was described and graded through a standard sieve stack. The fraction passing a No. 200 sieve was observed in petrographic grain mount and the amount of remaining lime paste was estimated to the nearest 25% by volume. Assuming an equivalency between volume and weight, this fraction was excluded from the gradation profile below. An error in this estimate is negligible given the small amount of this component. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 6.1: Acid Digestion Data - Weight Retention (g) Sieve size M2 M3 M4 3/8" 0.00 0.00 0.00 No. 4 0.00 0.64 0.00 No. 8 0.19 0.34 0.04 No. 16 0.94 0.61 0.14 No. 30 6.39 1.59 1.55 No. 50 8.25 1.40 1.77 No. 100 1.67 0.37 0.24 No. 200 0.37 0.11 0.04 Pan 0.16 0.03 0.00 Table 6.2: Acid Digestion Data - Cumulative Passing (%) Sieve size M2 M3 M4 3/8" 100.0 100.0 100.0 No. 4 100.0 87.4 100.0 No. 8 98.9 80.8 98.9 No. 16 93.7 68.8 95.1 No. 30 58.1 37.6 54.2 No. 50 12.2 10.0 7.5 No. 100 2.9 2.7 1.3 No. 200 0.9 0.5 0.1 Pan 0.0 0.0 0.0 Table 6.3: Acid Digestion Data - Cumulative Retained (%) Sieve size M2 M3 M4 3/8" 0.0 0.0 0.0 No. 4 0.0 12.6 0.0 No. 8 1.1 19.2 1.1 No. 16 6.3 31.2 4.9 No. 30 41.9 62.4 45.8 No. 50 87.8 90.0 92.5 No. 100 97.1 97.3 98.7 No. 200 99.1 99.5 99.9 Pan 100.0 100.0 100.0 Fineness modulus 2.34 3.13 2.43 Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Chart 6.1: Aggregate Sieve Analysis The following chart presents the particle size distribution curves for the extracted sand samples. The chart plots the data from the cumulative passing values in Table 6.2. The following should be noted: • The fine end of the curve is terminated at the No. 200 sieve. Any silt and clay components are not graded beyond this point and these are simply combined as the minus No. 200 fraction. • The curve for Sample M3 is somewhat irregular toward the coarse end. This is commonly observed when gradation curves are drawn from small samples and individual coarse particles represent a significant weight proportion of the whole. 0 10 20 30 40 50 60 70 80 90 100 0.01 0.10 1.00 10.00 Cumulative percent passing (%) Grain size (mm) CHRI.Mortar.2 CHRI.Mortar.3 CHRI.Mortar.4 Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site 7. Chemical Analysis The challenge for these particular types of mortar is that the coralline sand is nearly as acid-soluble as the cured lime binder making it difficult to separate the two chemically for individual measurement. The laboratory has used a proprietary modification of ASTM C1324 to overcome this difficulty. While there may be some small errors, results should be considered within several percent of the true values. The following steps have been taken: • A representative subsample of each mortar is taken. • The mortar is mechanically disaggregated and a small aliquot of finer material that can be suspended in water is separated out and reserved for chemical analysis. This is assumed to represent an accurate subsample of the binder with some minor silt and clay derived from the sand. • The remaining coarse material is mechanically disaggregated and washed in mild acid (Section 6). This removes any remaining binder that was not subsampled in the last step. This material is discarded. The coarse material represents the total percentage of aggregate relative to the original subsample (Table 7.2). All that is missing is any silt captured with the fine binder portion. • Subtracting the aggregate percentage from 100% yields the percentage of binder plus any silt and clay. • Since the binder matrix appears uniform, the smaller aliquot of fines separated out initially may be considered to be a compositionally accurate subsample. The chemical analysis in this section is performed on this smaller aliquot (Table 7.1). The measured chemical oxides plus any insoluble residue and losses on ignition are proportionally normalized to fill the difference between 100% and the measured aggregate. • After this normalization, the insoluble residue measured with the binder is added back to the initial sand measurement to add back any silt and clay that was removed initially. The combined analysis (Table 7.3) can now be treated as any lime mortar analysis would be using the standard calculation methods of ASTM C1324 (Table 7.5). Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 7.1: Chemical Analysis Results (Disaggregated Fines) As described in Section 6, mechanical disaggregation of each mortar sample produced a coarse fraction used to determine a sand gradation, and a fine fraction mostly representing the lime binder. The latter was recovered as a fine powder decanted from the disaggregated mortar, suspended in water, and evaporated to dryness. The chemical analysis was performed on this recovered powder. The powder was subjected to a typical chemical analysis procedure to determine soluble oxides, insoluble residue, and losses on ignition. The digestion procedure was modified from that in ASTM C1324 to account for the lime binder. The method includes a room temperature acid digestion and excludes the base digestion used for siliceous binders. The insoluble residue was taken from this same digestion rather than from the digestion of a separate aliquot. Sample ID M2 M3 M4 Component (wgt. %) SiO2 BDL 0.63 0.10 CaO 49.11 42.00 47.00 MgO 0.64 1.71 1.38 Al2O3 0.23 0.81 0.35 Fe2O3 0.07 0.39 0.08 Insoluble residue 2.73 11.82 3.94 LOI to110°C 0.22 0.49 0.40 LOI 110°C-550°C 3.03 4.18 3.54 LOI 550°C-950°C 40.24 34.49 38.83 Measured totals 96.28 96.53 95.61 Note: 1. For Sample M2, the measured SiO2 is below the detection limit. In this analysis, the detection limit for SiO2 is 0.001% for a 1-g sample of the concentrated binder. Table 7.2: Chemical Analysis Results (Coarse Fraction) The coarse fraction of the disaggregated mortar was further processed with mild acetic acid to clean surfaces of residual lime as described in Section 6. The table shown here reports the cleaned sand as weight as a percentage of the total sample. Sample ID M2 M3 M4 Component (wgt. %) Sand 64.66 44.44 32.57 Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 7.3: Chemical Analysis Results (Total Mortar) The total chemistry is calculated by adding the measured aggregate residue from the coarse fraction (Table 7.2) and a normalized amount of all of the components from the fine fraction (Table 7.1). The lime binder and any intermixed silt is assumed to be uniform so that any fines washed from the sand surfaces can be assumed to have the same composition as that of the fine fraction measured chemically. As such, the soluble oxides, sand, and losses on ignition presented in the table below are proportionalized up to the difference between the coarse fraction and the initial sample weight. This is summed with the fine fraction to produce a complete analysis of the mortar. Sample ID M2 M3 M4 Component (wgt. %) SiO2 BDL 0.36 0.07 CaO 18.03 24.17 33.15 MgO 0.24 0.99 0.98 Al2O3 0.09 0.47 0.24 Fe2O3 0.03 0.23 0.06 Sand 65.66 51.24 35.35 LOI 45°C-110°C 0.08 0.28 0.28 LOI 110°C-550°C 1.11 2.40 2.50 LOI 550°C-950°C 14.77 19.86 27.39 Measured totals 100.00 100.00 100.00 Note: 1. For Sample M2, the measured SiO2 is below the detection limit. In this analysis, the detection limit for SiO2 is 0.001% for a 1-g sample of the concentrated binder. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 7.4: Normalized Lime Compositions The binder in each of the three mortar samples is interpreted to consist of a nonhydraulic lime with no other additives. As such, the lime chemistry is estimated from the chemical analysis presented in Table 7.1. The five major oxides in the binder are normalized to a 99% weight yield. This normalizes the lime to a dry weight basis and is equivalent to the pre-slaked condition. The residual 1% is assumed to represent trace unmeasured constituents. Important chemical indices are calculated as follows: Hydraulic index = (SiO2 + Al2O3) / CaO Cementation index = (2.8·SiO2 + 1.1·Al2O3 + 0.7·Fe2O3) / (CaO + 1.4·MgO) The following features are worth noting: • Samples M2 and M4 have CaO contents over 95% and are considered to be high-calcium products with very little impurity. These likely slaked readily and produced a higher volume of lime putty upon slaking. • The high calcium contents would be consistent with lime burned from coral though not diagnostic of that source. • The soluble chemistry in Sample M3 contains only 91% CaO and a modest amount of impurity. This includes almost 4% MgO. This sample is one in which a coral source for the lime is more certain based on petrographic evidence. This level of impurity would not be typical for this type of lime. Instead, it is suspected that portions of the volcanic sand had solubilized through reaction with the alkaline lime paste prior to carbonation, and is available for chemical measurement after acid digestion. While this type of reaction might be considered analogous to a pozzolanic reaction, there is no evidence to indicate any true hydraulicity. • Hydraulic indices less than 0.1 and cementation indices less than 0.4 are generally taken to indicate an absence of any appreciable hydraulicity (Eckel, 169-173). None of the limes show any chemical sign of a hydraulic property. Sample ID M2 M3 M4 Component (wgt. %) SiO2 0.0 1.4 0.2 CaO 97.1 91.3 95.1 MgO 1.3 3.7 2.8 Al2O3 0.5 1.8 0.7 Fe2O3 0.1 0.9 0.2 Other 1.0 1.0 1.0 CaO/MgO 76.5 24.5 34.0 Hydraulic index 0.00 0.03 0.01 Cementation index 0.01 0.07 0.01 Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Table 7.5: Calculated Components Two separate volume estimates are given in the table below. One is given with the lime in the form of a dry hydrate despite the fact that the mortars examined for this report predate the commercial availability of prepackaged hydrated lime. Calculating the lime as a dry hydrate is convenient because it does not have to take into account the mix water used in a lime putty. It also allows for a more direct assessment of possible repair formulations using modern bagged masonry lime. Nonetheless, it is generally assumed that a volume of dry hydrate will lose approximately 20% of its volume when water is added to produce a putty of stiff consistency. This assumption is the basis for the volume estimate reported for lime putty. This ratio is derived from the dry hydrate calculation. It should also be noted that where volume proportions are given, these are based on estimated original bulk densities of the materials. However, limes are subject to great variation in volume due to factors such as settling or “fluffing” in dry powders and mix water content in putties. The table also presents the weight percentages of the dry ingredients (dry hydrated lime and sand). These are more accurate as they represent direct measurements of material mass and are not based on assumptions of bulk density. Of course, all of these discussions may be academic since it is usually desirable to modify the original design if modern materials will be used to replace their historic counterparts. The findings of a mortar analysis are best used to constrain possible repair designs rather than as a prescription for a specific formulation. Sample ID M2 M3 M4 Component Lime expressed as dry hydrate (wgt. %) 27 40 56 Sand (wgt. %) 73 60 44 Lime : sand ratio (by volume with lime as dry hydrate) 1 : 1.4 1 : 0.74 1 : 0.39 Lime : sand ratio (by volume with lime as putty) 1 : 1.7 1 : 0.93 1 : 0.48 Notes: 1. The component proportions are calculated from the total mortar chemical analysis presented in Table 7.3. The lime weight is calculated by mathematically converting the measured CaO and MgO to their respective hydroxides by molecular weight conversion. The three other measured oxides are assumed to represent minor impurities in the lime and are added directly to the calculated hydroxides. The total represents the lime in the form of a dry hydrate. The sand is taken directly from the weight of the sand presented in Table 7.3. The lime and sand weights are then normalized to 100% to return the materials to a dry weight basis. 2. Volumetric ratios are calculated assuming bulk densities for nonhydraulic lime and damp, loose sand of 40 lbs./ft.3 and 80 lbs./ft.3, respectively. Another calculation is provided assuming the lime in putty form. This assumes a unit of dry lime hydrate will lose approximately 20% of its volume when mixed to the consistency of a stiff paste. References Eckel, Edwin C. Cements, Limes, and Plasters. Their Materials, Manufacture, and Properties. New York: Robert Drummond, 1905. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Appendix I: Photographs and Photomicrographs Microscopic examination is performed on an Olympus BX-51 polarized/reflected light microscope and an Olympus SZ40 stereoscopic microscope. The polarized light microscope is fitted with a Tucsen MIchrome 5 Pro 5MP digital camera. The stereoscopic microscope is used for simple magnification. Sample types examined under this microscope include fractured surfaces, fine constituents extracted through chemical or physical means, or honed or polished cross sections. The polarized light microscope (PLM) magnifies but also employs principles of optical crystallography. The most common sample preparation for the PLM is the petrographic thin section. For this preparation, cross-sectioned samples are mounted to glass slides and are milled to a thickness sufficient to allow light to be transmitted through the material. These are usually prepared without water and with minimal heat to avoid altering minerals that are water or temperature-sensitive. In many cases, the samples are impregnated with a low-viscosity, blue-dyed epoxy. When so treated, blue areas represent some type of void space (e.g., air-voids, capillary pores, cracks, etc.). The polarized light photomicrographs are taken using a variety of optical settings chosen to best demonstrate the feature(s) of interest. These are distinguished as follows: Plane polarized light (abbreviated as PPL) This method uses the refractive power of different constituents to produce an artificial sense of surface relief. Otherwise, the method is the closest to a simple magnification of the material. The setting is often used to demonstrate granular relationships or microstructure. Pore spaces and cracks are observable with this setting if the blue-dyed epoxy is used. Conoscopic polarized light (abbreviated as CPL) In this setting, the transmitted light is condensed just before passing through the thin section. The method tends to bring colors or finer particulates into higher contrast at the expense of image sharpness. The setting is often used to image grain boundary failures in dimension stone, pigment particulates in binders, or gel phases in the micropores of cement pastes. Cross polarized light (abbreviated as XPL) The setting places the thin section between two pieces of polarizing film oriented at 90° to one another. In isotropic materials (e.g., glasses, simple salts), all light is absorbed and the materials appear black. In anisotropic crystals, two light rays traveling at different speeds are produced within the thin section and these offset waves interfere at the upper polarizing film. The interference produces a color that can be used to calculate properties of the crystal structure and aid in identification of mineral species. In essence, the colors are artificial. It should be noted that color is a function of orientation and color differences do not necessarily indicate material differences. Compensator plates When in XPL mode, full-wave or quarter-wave compensator plates may be inserted into the light path to add or subtract interference. Technically, these methods are used to calculate properties of the crystal structure. However, they can also be used to alter the image appearance to help improve contrast between different constituents. They can also reveal preferred orientations in some materials (e.g., oriented residual crystallinity in fired ceramics). Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 1: Photographs of the mortar samples provided to Highbridge for examination. All material is light-colored with a warm hue. More intact pieces are shown at left in each image. The weighing dishes contain finer granules and powder. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 2: Close-up photographs of the mortar samples illustrate the grainy texture of the materials. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 3: Photographs illustrating the sand samples extracted by mechanical disaggregation followed by mild acid-washing. The coralline sands are buff-colored and soft-textured. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 4: The sand samples are shown after gradation through a standard sieve stack. All have relatively broad particle size distributions. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 5: PPL photomicrographs illustrating the various components of the coralline sand including green algae skeletons (GA), coral grains (C), snail shell fragments (SN), foraminifera tests (FM), and biomicritic limestone particles (BM). Some quartz sand (Q) is also shown here. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 6: XPL photomicrographs. Minor to trace amounts of siliceous sand grains are also present. Shown here are examples of volcanic grains (V), feldspathic volcanics (FV), and polycrystalline quartz (PQ). Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 7: PPL photomicrographs illustrating the overall microtexture of the mortar samples. The absorption of blue-dyed epoxy indicates that the binder (B) has high microporosity as is typical for high lime mortars. Note that the intensity is higher for Sample M3. This mortar has a higher microporosity and a softer quality in hand sample. This is interpreted to be the result of a higher original mix water content. Sand grains (S) are uniformly distributed throughout all mortars. Varying packing densities correlate with the different binder to sand ratios calculated for each sample. All mortars are well-consolidated and air-voids (AV) are minimal. One is shown only for Sample M4. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 8: PPL photomicrographs illustrating the microtexture of undispersed lime grains (LG) in each sample. Those in Samples M2 and M4 are relatively nondescript (upper images). The one in Sample M4 has a somewhat grainy microtexture. A few lime grains in Sample M3 have an unusual distribution of pores (P) with elongate rounded shapes (lower left). Note that these are quite similar to the pores present in the scleractinian coral particle shown at lower right. This suggests that the lime was burned from fossil coral. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Figure 9: PPL photomicrographs. Salt deposits are only observed petrographically in Sample M4. (Left) Calcium carbonate scale (CC) directly overlies the original tooled joint face but lies below one to two coats of lime wash (LW). (Right) Isotropic salts in pores (S) are optically consistent with chloride salts. Building Conservation Associates, Inc. Report #: SL1673-01R.1 Fort Christiansvaern National Historic Site Fort Christiansvaern and Stable Building Christiansted National Historic Site 2100 Church St. #100 Christiansted, VI 00820 www.nps.gov/chri National Park Service U.S. Department of the Interior EXPERIENCE YOUR AMERICA™