Concrete patching compound

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 installation of concrete patching compounds.
   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 of all surfaces to receive patching compound
2. Mixing and transportation of patching compound
3. Repairs to delaminated and scaled areas of existing concrete
4. Priming of repair areas and placement of patching compound
5. Finishing and curing of patches
6. Repair of cracks

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 comparable concrete repair 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. A skilled journeyman mason or cement finisher, trained and certified by the concrete repair system manufacturer shall be present at all times during concrete restoration and shall personally direct the work.
3. Contractor shall engage manufacturer’s technical representative at contractor’s expense, to provide:
   1. Periodic inspections of work in progress: As a minimum, manufacturer’s technical representative shall be present to review conditions and methods prior to start of work, and again when surface preparation has been substantially performed, but prior to patching, again when patching work is approximately 50% complete, and a final inspection shall be performed upon substantial completion of work.
   2. A technical representative of the manufacturer shall be present to supervise execution of the work to the extent deemed necessary by the manufacturer, in order to assure that all work is carried out in strict accordance with this specification.
4. Patching material must match the existing concrete as closely as possible in texture and color. Project Team and/or GSA Historic Preservation must approve the match and any of the patching that does not meet the standard per the approved mockup panels, must be removed and redone at 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, any necessary testing, and proposed general cleaning techniques, for approval once test panels are completed and approved.
   2. The manufacturer’s product literature for all proprietary products. If a custom-matched patch sample 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. Samples shall be fabricated on pieces of appropriate masonry from or on the building using the specified repair mortar as required.
   3. Written certificates from the patching materials manufacturer shall be submitted stating that all installers of the patching material have successfully completed a training workshop for installation of the patching material, or have met alternative workmanship qualifications acceptable to the manufacturer.
   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. Ongoing care and warranty requirements for all restored and newly installed materials.
   6. 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.
3. Testing and mockup panels shall be made using the appropriate cleaning, repair and patching methods as applicable to determine the best method to perform the work. The “best method” shall be defined as that which successfully cleans and provides a protective coating with no, or minimal, damage to the existing concrete.
4. The methods used, their application, etc. shall be in accordance with manufacturer’s instructions. GSA Historic Preservation shall conduct a thorough evaluation of each method after work is complete to determine the best method for the overall work.
5. The mockup shall include an evaluation of the materials and techniques proposed for the protection of surrounding areas from the chemicals used to repair and clean the concrete. Evaluation must include an evaluation of the method to be used to collect the cleaning effluent.
6. For proprietary cleaning systems, a representative of the cleaning materials manufacturer(s) shall be present during the preparation and application of the test areas.
7. Approved test panels shall become part of the work and shall serve as the quality standard for all similar work.
8. Each technician proposed for work on the project shall prepare a mockup panel. Technicians whose mockups are not approved shall not be permitted to work on concrete patching and repair.
9. Any testing, demonstrations or mockup that is rejected by the project team shall be removed in their entirety without damage to the surrounding concrete and a new demonstration/mockup shall be performed for the project team’s review.
10. Mockups shall include the following, as needed, and shall be performed in area(s) that will be exposed to the same weathering conditions as the building. Allow samples to cure at least three days before obtaining acceptance of color, texture and detailing match. Samples shall be viewed from an approved distance:
    1. Cleaning: Demonstrate materials and methods to be used for cleaning for each type of concrete surface and condition on sample panels each approximately 25 sq. ft. in area. Where necessary, test adjacent non-masonry materials for possible reaction with cleaning materials, or provide and prove complete protection. GSA HIstoric Preservation will decide which method is most appropriate and approve prior to starting work. Allow waiting period of duration indicated, but not less than seven calendar days after completion of sample panels for negative reactions.
    2. Paint, Graffiti, and Metallic Stain Removal: Demonstrate materials and methods to be used for paint, graffiti, and stain removal for each type of surface and condition on sample panel 4 sq. ft. in area. The removal method or methods shall be tested on an inconspicuous area of the building as approved by GSA Historic Preservation.
    3. Crack Repair: Prepare a sample area for each type of crack repair required for stone (i.e. hairline cracks and microscopic cracks 1/64”-1/16” in size; cracks and voids larger than 1/8”). Repair shall demonstrate methods and quality of workmanship expected for crack repair and as approved by the project team and/or GSA Historic Preservation.
    4. Patching: Prepare on-building sample of each type of construction to be patched, rebuilt and/or replaced, in locations approved by GSA Historic Preservation. Patching shall demonstrate methods and quality of workmanship expected of repair work.
    5. Source of Materials: Obtain materials for patching, coating, sealing and crack repair from a single source manufacturer to ensure match quality, color, texture and detailing.

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

1. The Contractor shall:
   1. Deliver restoration cleaning and testing 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). Store in a dry, protected location.
   2. 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.
   3. Deliver and store restoration material in manufacturer’s original, unopened containers with the grade, batch and production data shown on the container or packaging.
   4. Collect and dispose of waste material, packaging, debris, and effluent associated with the work in accordance with local, state, and federal environmental regulations.
   5. Comply with the manufacturer’s written specifications and recommendations for mixing, application, and curing of grouts and patching materials.

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).

1.09 Project/site conditions

1. Clean masonry surfaces only when air temperatures are above 40℉ and will remain so until concrete has dried out, but for not less than seven (7) days after completion of cleaning.
2. Patching shall occur only when air temperatures are between 40℉ and 86℉ and will remain so for at least 48 hours after completion of work. Do not perform any patching work if precipitation is expected. In case of unexpected precipitation, work shall cease and all uncured material shall be adequately protected with an impermeable polyethylene sheet.
3. If either the ambient or subsurface temperature is expected to fall between 35℉ and 40℉ during curing and ultimate drying of the patching compound, then cold weather precautions shall be followed:
   1. Substitute materials as needed for the colder weather. Do not mix or place different grades together.
   2. Curing times shall be extended to compensate for lower temperature cure.
   3. Any material disrupted by early freezing must be removed and replaced under appropriate controls or conditions.
   4. If auxiliary heating will be used to protect freshly placed materials from freezing, equipment must not directly vent exhaust gasses onto the repair materials or into repair enclosure air. This may cause carbonation and low strength. Use moderate temperatures and heated air or radiant heat.
4. If ambient or surface temperature is expected to rise above 86℉ during application and curing of the patching compound, then hot weather precautions shall be followed:
   1. Substitute materials as needed for the hotter weather. Do not mix or place different grades together. Store all materials in a cool, shady location.
   2. Recooling of subsurface shall be carried out by continuous wetting at least one hour before placing patching compounds. This shall be done by covering or draping the entire repair area with burlap and by continuously keeping the burlap wet. The burlap shall be removed just prior to the patching of each area, as work proceeds.
   3. In hot, dry, windy weather, repair areas shall be covered or draped with burlap for a minimum of 3 hours after patch placement, to avoid rapid drying of the patches. Maximum wet cure time shall not exceed 24 hours.
5. Prevent masonry patching materials from staining the face of other surfaces to be left exposed. Immediately remove all patching materials that come in contact with such surfaces.
6. Cover partially completed work when work is not in progress.
7. 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.
8. At a minimum, the Contractor shall:
   1. Protect sills, ledges and projections from droppings.
   2. Protect woodwork, glass, metal, and any material adjacent to work areas to be cleaned from overspray and possible chemical or water damage from cleaning operations. Cover all window openings with waterproof plastic to prevent leakage to the building interior.
   3. Protect surrounding vegetation from runoff during cleaning operations.
   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.
9. 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. Masonry cleaning is to be completed prior to restoration of windows, doors, and metalwork, and prior to any exterior painting in the affected areas.
10. 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. Acrylic latex primer/bonding agent
2. Patching compound shall be an acrylic polymer modified blend of portland cement, specially graded aggregates and admixtures, designed for low shrinkage, low stress cure, and compatibility with existing host concrete. Prior to patching, sample cores of existing concrete shall be delivered by Contractor to manufacturer for testing and evaluation. Patching compound shall be customized by manufacturer, so that compressive strength does not exceed 4000 psi, or 500 psi above the existing concrete’s compressive strength, whichever is higher, as measured by ASTM C-109. Manufacturer shall have a successful performance history for similar projects of no less than 10 years, and shall have been doing business as the same business entity for no less than 10 years. Patching compound shall develop a minimum 200 psi direct tensile adhesion with host substrate, when applied in accordance with these specifications. Tensile strength of patching compound shall be a minimum of 400 psi. Flexural modulus shall be 1.1 x 106. Material must be vapor permeable, with a minimum permeance of 8 perms at 1/2” depth as measured by ASTM E-96, or as specified by Architect. No colorants, accelerators, bonding agents or other additives shall be added to the patching compound without express written direction of the manufacturer.
3. Crack sealant for small cracks shall be a 100% solids, 2-component elastomeric epoxy with 110% elongation and minimum 1200 psi tensile strength as measured by ASTM D412, or as specified by Architect.
4. Reinforcing steel primer/corrosion inhibitor shall be an alkaline, silica fume modified, latex modified cementitious coating, or as specified by Architect
5. Water: for cleaning, mixing and finishing shall be clean, potable, free from oil, acid, injurious amounts of vegetable matter, alkalies or other salts.

Part 3 - Execution

3.01 Sequencing

1. Concrete restoration work shall be performed in the following order:
   1. Remove paint, stains and plant material from all surfaces, in a manner and using materials approved by GSA Historic Preservation
   2. Remove existing unsound materials from areas indicated to be restored
   3. Pressure wash building and repair surfaces as indicated
   4. Patch and repair existing concrete structures as indicated
   5. Provide consolidation/water repellent treatment for concrete structures as indicated, if necessary.
   6. Provide special coating over indicated sections as indicated, if specified

3.02 Surface preparation

1. Remove all unsound concrete to render a surface clean with complete exposure of sound original material without any deposits of contaminants, foreign matter or loose material, which could affect the bond or long-term durability of the surface and the patching compound:
   1. Use lightweight demolition hammers, not to exceed 18 pounds in weight.
   2. All removals to be performed in accordance with ICRI Guideline #03730, which shall be a part of these specifications, with regard to removal geometry, exposing, undercutting and cleaning of embedded reinforcement, and conditioning of edges and surfaces.
   3. Following demolition, test surfaces for alkalinity/carbonation with a 1-2% solution of phenolphthalein.
   4. Surfaces which do not indicate alkalinity (solution turns pink) shall require further demolition.
2. Cleaning Methods:
   1. Pressure wash all indicated surfaces using 3000-4000 psi water blast, as required to remove all dust and dirt.
   2. Abrasive shall be used in combination with water when cleaning repair cavities, as required to eliminate micro- cracked surface materials resulting from demolition.
   3. No water with concrete dust shall be allowed to remain on any surface following washing, and must be immediately removed, prior to drying and rehardening

3.03 Crack repair

1. Prior to crack repair, contractor shall engage the services of the crack sealant manufacturer’s technical representative to assist in the selection of the appropriate grades of crack sealants for each area. Patching compounds are not to be used to bridge working cracks or joints.
2. Crack repair for small cracks less than 1/16” (62 mils, 1.5 mm) shall be performed following pressure washing and drying by gravity filling with elastomeric crack sealant. Cracks wider than than 1/16” shall be grooved out to a nominal 1/2” x 1/2” (3mm x 3mm), and filled with crack sealant.

3.04 Priming of reinforcing steel

1. Clean and prepare any steel reinforcement exposed in the course of removing unsound materials as specified. Replace if necessary.
2. Apply cementitious corrosion inhibitive primer and bonding agent to all steel surfaces in accordance with manufacturer’s instructions. Ensure a continuous coating on the full surface, including the underside of the undercut reinforcement.
3. Observe manufacturer’s guidelines for timing of patching after application of primer.

3.05 Concrete patching

1. All repair areas to be patched shall be kept continuously wet for at least 20 minutes prior to application of patching compound. Before placing patch, excess water shall be blown, vacuumed or otherwise removed from the surface, leaving the surface damp or saturated/surface dry.
2. Vigorously brush apply a thin primer coat of acrylic latex bonding agent with added 10% neat Type 1 portland cement into all cavity surfaces.
3. Mix and place patching compound in accordance with manufacturer’s instructions, within four (4) hours of primer application.
4. Mix the precisely measured quantity of water specified by the manufacturer with full bags of patching compound only.
   1. use slow speed drill (450 rom maximum) with mud or paddle mixer
   2. Motorized mortar mixers may be used for mixing larger quantities
   3. Mix for precisely 4 minutes
   4. Mix to a uniform consistency, free of lumps or dry material. Take care not to whip air into the mix or to overmix.
   5. Dispose of any mix that does not mix correctly, and mix a new batch.
5. When placing the patching compound, ensure that all corners and gaps under reinforcing steel and entire cavity profile is completely filled and properly compacted to prevent formation of voids or unbonded areas.
6. Move the material into corners and gaps, and onto cavity side walls using pressure on the trowel to ensure contact between patch and substrates.
7. Patches deeper than 1” (25 mm) may be extended by coarse aggregate addition. Proposed aggregate shape, color, and mix proportions must be approved by the Project Team and/or GSA Historic Preservation.
8. Material which has begun to set may not be retempered. Discard any unused material after 20 minutes. Limit surface water addition to light misting. Do not excessively wet patch surfaces after placement or as an aid to trowelling.
9. Observe curing requirements for each day’s working conditions, as specified herein. Do not extend wet curing beyond the maximum specified. Do not open to traffic or expose to weather until adequate strength has been reached, as affected by working and curing conditions. Do not apply deicing salts on or near the concrete until deemed fully cured.

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.