Terrazzo repair specification

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 the restoration of terrazzo flooring.
   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. Regrinding of terrazzo floors
2. Preparation of surfaces for patching
3. Repairs of delamination
4. Crack repairs
5. Placement of patching matrix
6. Finish and curing of terrazzo

1.03 Section includes

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 terrazzo cleaning and restoration and shall have successfully completed at least three projects of similar scope within the previous five years. Installer shall be a contractor member of NTMA (National Terrazzo and Mosaic Association)  in good standing and shall perform all work in accordance with NTMA standards. 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.

1.05 Submittals

1. The Contractor shall submit to the Architect or GSA Approving Official:
   1. Identification of existing terrazzo system (epoxy, or cement) submitted in writing. All proposed methods and materials must be compatible with identified system.
   2. A detailed description and schedule of the areas to be treated, including an assessment of the problem surfaces, any necessary testing, and proposed general cleaning, polishing and repair techniques.
   3. A detailed description and schedule of areas for grinding.
   4. All cracks shall be identified as No Action (NA), Repair Crack (RC), or Replace Terrazzo (RT), in accordance with the standards set in this specification and with the GSA Historic Preservation. Crack classifications are to be reviewed and approved prior to the start of work.
   5. The manufacturer’s product literature for all proprietary products. If a custom 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.
   6. Cleaning techniques should be submitted to GSA Historic Preservation for approval prior to implementation and mockups may be needed to protect adjacent historic surfaces.
   7. 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.
   8. Ongoing care and warranty requirements for all restored and newly installed materials.
   9. 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. The “best method” shall be defined as that which successfully cleans and/or repairs the existing terrazzo with no, or minimal unavoidable damage to the existing terrazzo.
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.
3. Each worker proposed for work on the project shall prepare a mockup panel of each activity they are to work on. Terrazzo workers whose mockups are not approved shall not be permitted to work on terrazzo repair and replacement.
4. The methods used, their application, etc. shall be in accordance with manufacturer’s instructions and shall duplicate those procedures proposed for the terrazzo restoration work. GSA HIstoric Preservation shall conduct a thorough evaluation of each method after mockups are complete to determine the best method for the overall work.
5. Mockups shall include an evaluation of the materials and techniques proposed for the protection of surrounding areas.
6. For proprietary systems, a representative of the materials manufacturer(s) shall be present during the preparation and application of the test areas.
7. Approved mockups shall become part of the work and shall serve as the quality standard for all similar work.
8. 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.
9. Prepare the following mockups:
   1. Crack Repair: Prepare a sample area for each type of crack repair required (Hairline cracks 1/64” to 1/16” in size; cracks and voids larger than 1/8”). Repair shall demonstrate methods and quality of workmanship.
   2. Patching: Prepare on-floor, a sample of patching to include each type of repair required for the project. Patch shall demonstrate methods and quality of workmanship of patch repair.
   3. Cleaning including polishing.

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

1. The Contractor shall:
   1. Deliver all materials and proprietary products to the project site in manufacturer’s or distributor’s packaging, undamaged, complete with application instructions and Safety Data Sheets (SDS).
   2. Transport, store, and use 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.
   3. 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 hazardous material 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 waste as hazardous if it fails the TCLP.
2. 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.
3. 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.

1.09 Project/site conditions

1. The work of this Section shall be executed when all areas of the terrazzo are at a temperature within the product manufacturer’s recommended temperature range for application. Do not install terrazzo when temperature is below 50℉ or above 90℉. 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. 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.
3. At a minimum, the Contractor shall:
   1. Protect all materials adjacent to terrazzo and work area.
   2. 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.
   3. Interior work areas should be closed off from foot traffic as coordinated with building management. Contractor shall erect containment and increase air flow as necessary. Protection of adjacent materials and construction crew path through the building must be in place prior to the start of work and inspected on an ongoing basis. Reference building treatment plan.
   4. 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.
4. If applicable, the Contractor shall coordinate treatment operations with the other trades involved in exterior and interior restoration work.
5. 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.

Part 2 – Products

2.01 PRODUCTS

1. Cleaner: Potable water, free of iron, and/or chemical cleaners, all cleaners must be pH neutral
2. Sealer: Liquid type to completely seal matrix surface, compatible with terrazzo components
3. Grout: Color to match existing matrix unless noted otherwise
4. Matrix: Pigmented epoxy or cement to match approved sample
5. Aggregates: Aggregates to match approved sample
6. Divider Strips: Match width, material and color of divider strips, unless otherwise required
7. Control Joint Strips: Use same material and color as divider strips, unless otherwise specified
8. All work shall be executed with conventional terrazzo grinding equipment 

2.02 Equipment

1. Hand sander, small grinding tools
2. Grinding stones: Fine grit emery stones manufactured specifically for restorative type grinding and surfacing of terrazzo surfaces (#40 and #80 grit stones).
3. Resurfacing Screens: A fine grit screen manufactured specifically for restorative type grinding and resurfacing terrazzo surfaces.
4. Soft natural bristle brushes
5. Circular buffing machine (for floors) with grinding and polishing screens as recommended by NTMA. Use conventional terrazzo grinding equipment rather than lighter type machines.
6. Mop and bucket (non-metallic)
7. Sponges
8. Clean, dry cloths

Part 3 - Execution

3.01 General

1. Standards
   1. Resurface terrazzo in accordance with NTMA specifications.
   2. Grind and polish the terrazzo floor as required to produce a clean, smooth, and uniform finish, capable of being sealed and polished to match existing. EXERCISE CAUTION WHEN GRINDING NEAR COATED DIVIDER STRIPS.
   3. Hairline cracks are classified as less than 1/32” (0.030) as per the National Terrazzo and Mosaic Association (NTMA) guidelines.
   4. Replacement (RT) shall be from architectural break to architectural break, and should be performed only if necessary.
2. Resurfacing
   1. Grinding: Care should be taken to limit grinding and polishing to a small distance beyond the perimeter of the patch, until grout has been removed from the terrazzo surface. Avoid grinding divider strips.
      1. For small areas, sand surface with a hand sander or small grinding tool, using fine stones to achieve desired finish.
      2. For larger areas (such as floors), use a circular buffing machine with grinding and polishing pads as recommended by NTMA.
      3. Use a #24 or finer grit stone/screen (or as recommended by NTMA) for the initial grinding, exposing the marble chips. Fine mesh sand may be used if necessary. Follow with a fine #80 or finer grit stone/screen (or as recommended by NTMA).
   2. Rinse floor thoroughly with clean, clear water.
   3. Remove excess rinse water and machine or hand apply grout using identical Portland cement/acrylic or epoxy, color, and pigments as used in topping taking care to fill all voids completely.
   4. Cover grouted surface with paper or polyethylene for at least 72 hours.
   5. Final polish with a #80 or finer grit stone (or as recommended by NTMA), until grout has been removed from the terrazzo surface.
   6. Wash surface with neutral cleaner and thoroughly rinse with clean, clear water. Allow the surface to thoroughly dry.
   7. Seal terrazzo with a penetrating type sealer as recommended by manufacturer.
3. Epoxy Repair Crack (RC)
   1. Crack shall be cleaned of all loose material, dirt and coatings.
      1. Remove all foreign matter from the void, followed by routing with a power tool.
      2. Remove all sealer from the surface adjacent to the void with a stripper or ammonia.
   2. Crack shall be filled with resin to match existing color, texture, and hardness.
      1. Resin shall be standard 2-component epoxy resin, designed specifically for patching of terrazzo materials or approved alternative.
         1. Blend the resin materials to match the color matrix, by adding marble dust or pigment to match color of existing terrazzo matrix.
         2. Force mixed resin into the void, making sure it is pressured into the crack as deep as possible. In some cases, the supplier will instruct using a primer for their materials.
   3. If crack is wider than ¼” aggregate shall be used. Aggregate for epoxy shall be natural, sound, crushed marble chips without excessive flats or flakes, complying with NTMA requirements.
      1. Aggregate shall match existing in color and gradation of sizes. Chosen aggregate shall be submitted to GSA Historic Preservation for approval prior to mockup.
      2. Aggregate colors should be matched after cleaning or taken from the interior of core samples depending upon scope of work.
4. Cement Repair Crack (RC)
   1. If the binder of the existing terrazzo floor is Portland cement-based,  fine-line cracks or chips can be repaired using a cement grout. This is a more labor intensive repair than epoxy, but is usually more durable in comparison.
      1. Use a cement grout of approved color with approved aggregate mixture/blend, to match existing terrazzo matrix.
      2. Mix the grout into a thick paste and carefully work it into the cracked portion with the use of a putty knife.
      3. Once the grout is in place, a terrazzo mixture of marble chips and cement grout should be applied over the first layer of grout before it has dried.  Once the second layer is applied, level the area with a trowel.
      4. Once the mixture is leveled and dried, the area should be sanded down with a 40-grit sandpaper to be followed up with a finer grit, like the 80-grit sandpaper to further smoothen the repaired patch.
      5. After sanding the patch, seal the area with a clear penetrating sealer.  Note that the pH should be between 7 and 10.
5. Replace Terrazzo (RT)
   1. Areas deemed necessary for removal are to be removed carefully to prevent damage to surrounding existing terrazzo not scheduled for repair.
   2. Clean area and prepare for new terrazzo, using a mix that matches the existing in texture, color, and matrix (epoxy or cement).
   3. Repair substrate as needed. Fill cracks with hardening epoxy or, for epoxy systems only, use mesh isolation membrane to cover crack with liquid membrane.
   4. Place divider strips prior to pouring terrazzo topping.
   5. Fill area with epoxy or cement /cement matrix and approved aggregate mixture/blend.
   6. If repair is not to architectural break or existing terrazzo divider strip, the joining edge shall be a saw tooth (jagged edge). Intent is to disguise the line so it will blend into the rest of the terrazzo floor, irregularly place marble chips matching the existing terrazzo blend along the line, approximately one to two inches on center, while the patching resin is still in a wet state. Finally, tool off surface and allow to cure.
6. Replace Divider Strips, as needed
   1. Existing divider strips should be retained if possible. If replacement is necessary, due to missing or damaged divider strips, divider strips should be of solid composition and match existing in size, color, sheen and metal (brass, zinc, aluminum.). Do not use coated divider strips, unless specified.
   2. Install divider and control joint strips straight and level to locations indicated.
7. Control Joint Strips:
   1. Double or split units, 1/8” wide, of same material and color as divider strips with 1/8” wide full-depth filler, laminated between strips.
   2. Install base and border divider and control joint strips to match existing floor pattern.

3.02 Initial grinding

1. Areas for grinding of existing terrazzo should be agreed upon by the project team and carefully marked. For newly poured terrazzo, care should be taken to limit grinding and polishing to a small distance beyond the perimeter of the patch, until grout has been removed from the terrazzo surface. Avoid grinding divider strips.
2. When the material has hardened, sand surface with a hand sander or small grinding tool, using fine stones.
3. Wet or dry grind with appropriate medium diamonds/Stones as approved from mockup.
4. Grind with 24 or finer grit stone — fine mesh sand can be used if needed — all in the presence of water.
5. Follow initial grind with 80 or finer grit stones in the presence of water, but omit sand. 

3.03 Grouting

1. Cleanse floor with clean water and rinse. Wet grind with 50 or higher abrasive grit medium diamonds.
2. Remove excess water and machine or hand grout with cement/acrylic or epoxy material, with or without color added to match the matrix of the existing Terrazzo floor, to fill as needed. Make sure to fill all voids.

3.04 Curing grout

1. Allow grout to cure a minimum of 72 hours. Maintain ambient air temperature between 70°F (21°C) and 80°F (27°C). If necessary, Cover grouted surface with paper or polyethylene for at least 72 hours. 

3.05 Fine (final) grinding

1. Final polish with a #80 or finer grit stone. Care should be taken to limit grinding and polishing to a small distance beyond the perimeter of the patch, until grout has been removed from the terrazzo surface. Avoid grinding divider strips.

3.06 Cleaning and sealing

1. Wash all surfaces with a neutral cleaner, rinse with clean water and allow to dry fully.
2. Seal: Apply sealer per sealer manufacturer’s written directions. Interior floor sealer shall be odorless, slip and stain resistant penetrating sealer with pH factor between 7 and 10, that does not affect color or physical properties of terrazzo surface.
3. Remove protection and clean any adjacent surfaces affected by the refinishing process. If more than a wipe down is needed or material is adhered to adjacent surface, contact GSA Historic Preservation for recommendations on appropriate cleaning techniques. Cleaning techniques should be submitted to GSA Historic Preservation for approval prior to implementation and mockups may be needed to protect adjacent historic surfaces.

3.07 Protection

1. If necessary, Contractor shall protect the finished floor from all site activity until Substantial Completion.

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 repaired 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.