Patching Minor Chips and Cracks in Terrazzo with Cement Grout

CSI Division
Division 9 - Finishes
Section
Terrazzo
Last Modified

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Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.

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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. 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 SUMMARY

  1. This specification provides guidance on repairing small cracks in terrazzo floors by patching with cement grout.

  2. Minor chips and cracking in terrazzo require patching ONLY when surface irregularities present safety hazards or when it is necessary to prevent further deterioration to the terrazzo.

  3. Read “General Project Guidelines” along with this specification. These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO). The guidelines cover the following sections:

    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)

1.02 REFERENCES

NTMA Standards: Comply with specified provisions and recommendations of the National Terrazzo and Mosaic Association, Inc. (NTMA)

PART 2–PRODUCTS

2.01 MATERIALS

  1. Portland Cement: ASTM C150, Type I, except as modified to comply with NTMA requirements for compressive strength.

    1. Obtain cement from a single source for each required color.

    2. Provide non-staining white cement for terrazzo matrix.

  2. Sand: ASTM C33.

  3. Clean, potable water.

  4. Aggregate: Natural, sound, crushed marble chips that do not include excessive flats or flakes, complying with NTMA requirements.

    1. Colors and gradation of aggregate sizes as required to match original existing intact materials and patterns.

    2. NOTE: Original plans often contain the exact terrazzo mix.

    3. Aggregate colors should be matched after cleaning or taken from the interior of core samples depending upon scope of work.

  5. Matrix Pigments: Pure mineral or synthetic pigments, resistant to alkalis and non-fading. Mix pigments with matrix to provide required colors.

  6. Curing Compound: Liquid-membrane-forming compound, ASTM C309, Type 1.

  7. Grout: A cement acrylic grout with color added to match the matrix of the original terrazzo.

  8. Interior Floor Sealer: Colorless, slip and stain resistant penetrating sealer with a Ph factor between 7 and 10, which will not affect color or physical properties of terrazzo surface.

  9. Plastic Sheeting

2.02 EQUIPMENT

  1. Grinding Stones: Fine grit emery stones manufactured specifically for restorative type grinding and surfacing of terrazzo surfaces (#40 and #80 grit stones).

  2. Power saw or hand tools.

  3. Resurfacing Screens: A fine grit screen manufactured specifically for restorative type grinding and resurfacing terrazzo surfaces.

PART 3–EXECUTION

3.01 PREPARATION

  1. With a power saw or hand tools, cut a vertical perimeter wall around the area to be patched. If the patch is smaller than an inch square, slightly undercut this edge.

  2. Clean all debris from surface.

  3. Saturate void with water to prevent quick surface drying. Ensure that water penetrates into the surface in order to achieve a proper bond.

  4. Clean surfaces until any obstructing material has been removed.

  5. Apply cement paste and work into the surface. Do not allow cement paste to dry before placing terrazzo composition.

3.02 ERECTION, INSTALLATION AND APPLICATION

NOTE: Match marble chips and matrix for existing terrazzo by size, mineral content and color. Colors should be matched after cleaning or matched with samples taken from the interior of core samples, depending upon scope of work.

  1. Mix two parts blended marble chips with one part Portland cement and add enough water to make the mixture plastic.

  2. Place mixture over chip or crack and level with a trowel.

  3. Seed additional marble chips of the same blend over the patch, as required to establish a uniform coverage.

  4. Compact patch, removing all excess water and cement from the surface.

  5. Cover the patch with paper or polyethylene sheeting to prevent quick hydration.

  6. Cure until topping develops sufficient strength to prevent lifting or pulling of terrazzo chips during grinding.

  7. Sand surface with a hand sander or small grinding tool, using fine stones to achieve desired finish.

    1. Use a #40 or finer grit stone for the initial grinding, exposing the marble chips. Follow with a #80 grit stone before grouting with cement to fill all pinholes.

    1. CAUTION: IF DIVIDER STRIPS ARE COATED INSTEAD OF SOLID COMPOSITION, THEY SHOULD NOT BE GROUND. GRINDING MAY CAUSE COATED DIVIDER STRIPS TO LOSE THEIR COATING AND DISCOLOR.

    1. Cover grouted surface with paper or polyethylene for at least 72 hours.

    2. Thoroughly rinse the surface with clean, clear water.

    3. Remove excess rinse water

    4. Apply grout by hand or with a machine, using identical Portland cement, color and pigments as were used in topping, taking care to fill all voids completely.

    5. 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.

  8. Seal patch with a penetrating type terrazzo sealer.

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Last updated: Aug 13, 2017
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