Patching of sandstone

Technical procedures are supplied by GSA only as a reference. All procedures have been reviewed for general consistency with federal standards for rehabilitating historic buildings. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location.

References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.

Part 1 – General

1.01 Description

1. This specification provides guidance for patching of sandstone.
   1. This specification has been developed for use on historic properties (defined as any district, site, building, structure, or object that is listed in or eligible for listing in the National Register of Historic Places) and provides an overview of accepted practices. Site-specific specifications, when appropriate, will be provided by the Architect.
   2. All work described herein and related work must conform to the Secretary of the Interior’s Standards for the Treatment of Historic Properties.
   3. The Contractor shall provide all labor, material, equipment, and operations required to complete the rehabilitation work indicated herein.
   4. All work described herein and related work must have the approval of a Cultural Resources Manager, Conservator, Historic Architect, or other professional who meets the standards outlined in the Secretary of the Interior’s Standards – Professional Qualifications Standards pursuant to 36 CFR.

1.02 Section includes

1. Preparation for repairs
2. preparation of mortar
3. Repair of sandstone

1.03 Related sections

1. Section 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections and should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from GSA Historic Preservation:
   1. Safety Precautions
   2. Historic Structures Precautions
   3. Submittals
   4. Quality Assurance
   5. Delivery, Storage and Handling
   6. Project/Site Conditions
   7. Sequencing and Scheduling
   8. General Protection (Surface and Surrounding)
   9. Historic Building Treatment Procedures

1.04 Quality assurance

1. The Contractor performing the work described in this Section shall have a minimum of five years experience in construction and supervision of masonry restoration work on historic buildings, and shall have successfully completed at least three projects of similar scope within the previous five years. He/she shall demonstrate a working knowledge of The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring & Reconstructing Historic Buildings.
2. Masons, Installers, and Field Supervisors: Must be certified by the material supplier to install the specified products. All personnel involved with the work of this Section shall provide individual certificates to the Architect and/or GSA Historic Preservation documenting the successful completion of required training by the material manufacturer. If prior training has not been completed, job site training specific to this project will be required at the Masonry Contractor’s expense.

1.05 Submittals

1. The Contractor shall submit to the Architect or GSA Approving Official:
   1. A detailed description and schedule of the areas to be treated, including an assessment of the problem surfaces, and any necessary testing, for approval once test panels are completed and approved.
   2. The manufacturer’s product literature for all proprietary products. If a custom wax formula is used, all ingredients must be documented and submitted for approval as with proprietary formulas. Product literature shall include specification data, Safety Data Sheets (SDS), and instructions for storage, handling, and use.
   3. Submit certificates from the material supplier stating that field supervisors and masons installing the replacement material have successfully completed the training workshop for the installation of the stone repair material.
   4. A project safety plan to include at minimum: any personal protective equipment to be used by the contractor’s staff such as disposable clothing, gloves and safety glasses, procedures for emergencies and accidents, documentation of staff training in use of equipment and/or chemical products as required by the manufacturers.
   5. Material Samples: Before installation of sample to wall, submit each type of repair material showing proposed surface finish and color
   6. Restoration Plan: For each phase of repair work required provide detailed description of materials, methods, approach, tool selection, equipment, sequencing, and include the following:
      1. Measures for protection of surrounding materials on building and site.
      2. In-situ masonry preparation prior to repair.
      3. Removal of efflorescence (salt) from wall prior to repair.
      4. Measures to reduce existing excess moisture from masonry.
      5. Material curing methods after installation.
   7. Ongoing care and warranty requirements for all restored and newly installed materials.
   8. Provide a final report of completed work, including all approved submittals and photographs of the areas repaired that were taken before, during, and after the work.

1.06 Testing and mockups

1. Contractor, at inconspicuous locations designated by the Project Team and GSA Historic Preservation, shall perform small test patches (no larger than 6 inches by 6 inches) for all products to be used. Testing will determine the best method(s) to perform the work and ensure that the chosen products do not cause harm.
2. Following testing, mockup panels shall be created (mockup panels may incorporate successful test patches) using the chosen methods. Size and location of mockup panels shall be determined by the project Team and GSA Historic Preservation. The mockup shall include an evaluation of the materials and techniques proposed for the protection of surrounding areas during the work.
3. Testing and mockups shall be prepared for each type of replacement material on or using masonry removed from the building, if possible. Apply replacement material to the wall, or unit to be repaired according to specifications and manufacturer’s instructions. Prepare samples in an area where they will be exposed to the same conditions as will be present on the building during curing. Allow samples to cure at least seven days (or longer, if possible) before obtaining architects and GSA Historic Preservation approval for color match. Masonry materials will lighten in color as they cure. Samples should be viewed from a minimum distance of 15 feet.
4. Each mason proposed for work on the project shall prepare a mockup panel. Masons whose mockups are not approved shall not be permitted to work on stucco repair and replacement.
5. The mockup shall include an evaluation of the materials and techniques proposed for the protection of surrounding areas during the work.
6. Approved mockup panels shall become part of the work and shall serve as the quality standard for all similar work. Retain acceptable mockups in undisturbed condition as a standard for workmanship quality. Mockup to be used for judging completed work as the project progresses. Approval of work will be based upon: cleanliness, material color, texture, and finished profile.
7. Any testing, demonstrations, or mockup that is rejected by the project team shall be removed in its entirety without damage to the surrounding masonry and a new demonstration/mockup shall be performed for the project team’s review.

1.07 Delivery, storage, and handling (as applied to products and materials)

1. The Contractor shall:
   1. Materials are to be delivered, stored, and handled in such a way as to protect them from damage, extreme temperature, and moisture in accordance with Manufacturer’s written instructions.
   2. Deliver and store material in Manufacturer’s original, unopened containers with the production date shown on the container or packaging and Safety Data Sheets (SDS).
   3. Transport and store cleaning agents, chemicals, and solvents within the temperature range recommended by the manufacturer and away from direct sunlight. Handle all materials according to manufacturer’s instructions. Transport with Safety Data Sheets (SDS).
   4. Comply with the Manufacturer’s written specifications and recommendations for mixing, application, and curing of mortars.
   5. Collect and dispose of waste material, packaging, debris, and effluent associated with the work in accordance with local, state, and federal environmental regulations.

1.08 Safety

1. The contractor shall only use chemical products whose Safety Data Sheets (SDS) have been reviewed and considered acceptable by the Government. Any project surfaces containing lead-based paint, as disclosed by the Government, shall be handled by the contractor in accordance with OSHA (29 CFR 1926.62), EPA (40 CFR 261) and State regulations. Any lead-based paint or coating that is removed in a project resulting from this scope shall undergo Toxicity Characteristic Leaching Procedure (TCLP) testing by the contractor. The contractor shall dispose of any lead-paint waste as hazardous if it fails the TCLP.
2. Any paint or coating required to be removed which has not been disclosed by the Government to contain lead, shall be tested for lead by the contractor. All paints or coatings testing positive shall be handled and disposed of as lead-based.
3. The Contractor shall survey the project area for ACMs. All thermal systems insulation (i.e. boiler insulation, duct insulation, pipe insulation), surfacing materials (i.e. plaster and sprayed-on fireproofing) and miscellaneous materials (i.e. asphalt flooring, ceiling tiles, adhesives and mastics, drywall, roofing, gaskets and cement board), installed no later than 1980, must be considered asbestos containing unless proven otherwise in accordance with 29 CFR 1926.1101. Work involving the disturbance, dismantling or demolition of asbestos containing materials or structures containing asbestos; or the removal and disposal of asbestos, shall also comply with the requirements of 40 CFR Part 61, Subparts A and M; 29 CFR 1910.1001 (where applicable); and GSA Specification 02085 Asbestos Abatement Procedures.
4. The contractor shall isolate the work area with cones, tape or similar means as possible for the duration of the project, to prevent unauthorized individuals from entering the immediate work area.
5. For any work required on elevated surfaces (4 feet or more above the ground) the contractor shall install and use any ladders, scaffolding or platforms in accordance with OSHA regulations (29 CFR Subpart M).
6. All Contractor personnel performing treatment operations shall be provided by the Contractor with gloves, respirators, protective clothing and any other personal protective equipment (PPE) as recommended by the manufacturer of the products used during the work and required by local, state, and federal regulations.

1.09 Project/site conditions

1. The work of this Section shall be completed when the temperature is 40° F and rising. Maintain substrate surface temperature above 40° F for 48 hours after installation of repair mortars. Heated enclosures to maintain specified temperatures are permitted with Architect approval. Exterior work shall not commence when rain, snow, or below-freezing temperatures are expected within the next 24 hours. All surfaces shall be free of standing water, frost, and ice.
2. Hot Weather Requirements: Protect repair mortar from direct sunlight and wind. Do not use or prepare mortar when ambient air temperature is above 95° F or surface temperature of substrate is in excess of 105° F.
3. The Contractor is responsible for protecting existing adjacent areas and materials during the execution of the work and shall provide all necessary protection and follow all necessary work procedures to avoid damage to existing material assemblies and vegetation not a part of the work of this Section.
4. Exterior work areas should be accessed from the exterior only. Under no circumstances are hoses to be run or equipment transported through the building during exterior cleaning operations.
5. If necessary, the Contractor shall erect waterproof enclosures around areas where treatment operations are in progress to protect nearby property and passers-by from overspray of chemicals or rinse water.
6. If applicable, the Contractor shall coordinate treatment operations with the other trades involved in exterior and interior restoration work, including but not limited to masonry restoration, sealing, and painting. 

Part 2 – products

2.01 Materials

1. Mineral Based Natural Repair Mortar for Sandstone
   1. Formulation: Pre-blended, mineral-based, single component repair product.
   2. Color: Match to the existing in-situ masonry.
   3. Texture: Match to existing in-situ masonry.
2. Acrylic bonding agents, accelerators, and retardants are NOT permitted for use.
3. Admixtures:
   1. No synthetic polymers or additives are permitted in the formulation.
   2. No air-entraining admixtures are permitted.
   3. No antifreeze compounds, chlorides or other additives are permitted.
   4. Color pigments are permitted only with prior written approval from the material manufacturer. 

2.02 Factory mixing

1. Pre-blend all replacement materials into single containers in a factory-controlled environment.
2. Mixing of individual ingredients at the construction site shall not be permitted.
3. Match color and texture of replacement material to the original material
4. Mark all containers to include manufacturing date and batch number. Maintain production sampling procedures for each batch and shipment for quality control tracking purposes.

Part 3 - execution

3.01 General

1. Keep all replacement materials from smearing / staining adjacent surfaces. Adjust water content of material during placement to execute the cleanest work possible without compromising material performance. If needed, request assistance from the manufacturer to establish water content ratio to meet this requirement.
2. Contractor must maintain clean masonry surfaces throughout the project.

3.02 Preparation for repairs

1. Prior to the start of repair, the sandstone must be fully inspected and documented with all defects and needed repairs documented, both written and photographic,  and submitted to the project team.
2. “Sound” masonry with a hammer to verify its integrity. Cut or chip out all loose stone with a hammer and cold chisel to a minimum thickness of 1/2”. Undercut the stone so the patch will lock firmly. Remove any sealant residue.
3. Where cramp anchors, threaded rod anchors, or dowels have been cut and pieces remain embedded in the substrate: Anchors that are free of rust, solidly embedded, and do not project beyond the surface of the masonry unit may remain. All others should be removed.
4. Cut the edges of the repair area to provide a minimum depth of 1/4”. Repair area should not be less than 1/4” in depth. The edges of the repair should be square cut. Do not allow any feathered edges in the repair area.
5. Fully treat any areas of efflorescence (salt deposits), as approved by Project Team and/or GSA historic Preservation, prior to application of mortar; Project team must approve completed efflorescence treatment prior to continuing with project.
6. Install mechanical anchors in all repair areas if specified on the Contract Drawing or as otherwise directed by the Specifier.
7. Clean all dust from the surface and pores of the substrate, using clean water and a soft scrub brush.
8. For very dry or porous surfaces, pre-wet the substrate ahead of time to prevent the substrate from drawing moisture out of the repair too quickly. Re-wet the surface immediately before applying the repair material.

3.03 Mortar preparation

1. Morat shall be mixed on site. Mix only what can be used within a 30 minute period. Discard any unused mixed material after 30 minutes.
2. All repairs require a minimum two-coat application consisting of a skim coat and a build-out coat. Additional build-out coats may be applied to meet the required thickness.
   1. Skim coat: For the initial skim coat, mix approximately five (5) parts dry powder (dry powder mix is as approved by the Architect and/or GSA Historic Preservation to match existing in color, texture, and hardness) to approximately one (1) part potable water. The prepared mixture should be the consistency of peanut butter. Temperature and humidity will affect the amount of water required. Mixing may be done by hand or using a low-speed drill (300 to 450 rpm) for two (2) to four (4) minutes. Do not over mix.
   2. Build-out coat: The consistency of the mortar for the build-out coat should be similar to wet sand. For any additional build-out coats use slightly less water in the mix. Working time is approximately sixty (60) minutes depending on temperature, humidity and wind conditions.

3.04 Application

1. Skim Coat: Follow Manufacturer’s directions. Pre-wet the substrate so it is wet but with no pooling water. Remove loose material and wash down with additional water a second time. Ensure that the skim coat adheres to all surfaces of the repair area. Do not allow the surface of the skim coat to dry completely before applying build-out coat(s).
2. Build-Out Coat: Follow Manufacturer’s directions. Use slightly less water for additional build-out coats. Mortar may be built up to a thickness of no greater than 3” in one lift. Pre-soak the previously applied repair material with water if additional coats are necessary the following day.

3.05 Finishing

1. Tool the surface of the patch to match existing. Finishing techniques must be approved through a mockup by the Project Team and/or GSA Historic Preservation prior to implementation. Only masons who’s finishing techniques have been approved may perform this work. Craftsmen are required to understand the timing of the finishing techniques, and make adjustments for weather conditions. Pneumatic chisels can be used to create the desired finishes. Finish work that does not match the surrounding existing materials will be redone at Contractor’s expense.
2. Finishing may be performed by one of the following, or alternate approved method:
   1. Acid etching: After the surface has cured 48 hours, brush on Technical Grade hydrochloric acid, diluted 1:5 with water; Rinse the surface thoroughly with clean, clear water.
   2. Rubbing stones: Coarse or fine grade (grits #60, 80, 100, 120); Use dry or with water to hone the surface of well cured repairs.
   3. Stipple with a damp sponge or dry-towel with a wooden float.
   4. Score partially cured repair with stone tools to match original tool marks and patterns.

3.06 Curing

1. Keep the repair area, plus an additional two (2) inches surrounding the repair area damp for a minimum of thirty-six (36) hours. Spray the repair area with clean water, covering with plastic sheeting to keep the repair area damp. Adjust curing methods to prevent the repair from drying out too quickly.
2. Curing methods will vary depending on the climate and weather conditions. The amount of water to be used in the first thirty-six (36) hours after application shall be adjusted as needed. Adjustments to these curing procedures must take into account the remaining time prior to freezing weather conditions.
3. Following curing, all patches must be inspected for hairline cracks, separation of patch from substrate, and mismatching of color and texture to surrounding existing stone. 

Part 4 – Final report

4.01 Final report

1. The Contractor Shall:
   1. Provide a final report of completed work, including all approved submittals and photographs of the areas cleaned that were taken before, during, and after the work.
   2. Provide a written summary of the project and results upon final inspection and approval. The summary shall include a discussion of steps taken or new findings not specified in the initial documentation. Summary should also include any applicable ongoing care and warranty requirements.