Regrinding Terrazzo Floors

CSI Division
Division 9 - Finishes
Section
Terrazzo
Last Modified

Technical Procedures Disclaimer

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.

THIS PROCEDURE SHOULD ONLY BE PERFORMED BY AN EXPERIENCED PROFESSIONAL AND ONLY UPON APPROVAL FROM THE REGIONAL HISTORIC PRESERVATION OFFICER (RHPO).

THIS PROCEDURE SHOULD BE PERFORMED UNDER THE DIRECTION OF AN HISTORICAL ARCHITECT TO DECIDE THE MOST EFFICIENT AND LEAST DESTRUCTIVE MANNER FOR EXECUTING THE WORK.

PART 1—GENERAL

1.01 SUMMARY

  1. This procedure includes guidance on resurfacing terrazzo floors to remove sealers and coatings when normal stripping and cleaning is not sufficient to restore the floor to its original luster.

    CAUTION: THIS METHOD OF REMOVING SEALERS AND COATINGS INVOLVES GRINDING OFF A THIN LAYER OF THE TERRAZZO. IT SHOULD ONLY BE USED AS AN EXTREME MEASURE AND A SPECIALIST MUST BE CONSULTED.

  2. See 01100-07-S for general project guidelines to be reviewed along with this procedure. These 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)

These guidelines should be reviewed before performing this procedure and should be followed, when applicable, along with recommendations from the RHPO.

1.02 REFERENCES

  1. NTMA Standards: Comply with specified provisions and recommendations of National Terrazzo and Mosaic Association, Inc. (NTMA), www.ntma.com
  2. ASTM Standards: Comply with specified provisions and recommendations of American Society for Testing and Materials (ASTM), www.astm.org

PART 2—PRODUCTS

2.01 MATERIALS

  1. Portland Cement: ASTM C150, Type I, except as modified to comply with NTMA requirements for compressive strength. Obtain cement from a single source or each required color.
    1. Provide nonstaining white cement for terrazzo matrix.
  2. Sand: ASTM C33
  3. Clean, potable water
  4. Aggregate: Natural, sound, crushed marble chips without 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. Original plans often contain the exact terrazzo mix.
    2. Aggregate colors should be matched after cleaning or taken from the interior of core samples depleting upon scope of work.
  5. Matrix Pigments: Pure mineral or synthetic pigments, resistant to alkalies 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 Ph factor between seven and ten, that does not affect color or physical properties of terrazzo surface.
  9. Kraft paper or plastic sheeting

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 (#24 and #60 grit stones, or as recommended by NTMA).
  3. Resurfacing Screens: A fine grit screen manufactured specifically for restorative type grinding and resurfacing of 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 ERECTION, INSTALLATION, APPLICATION

NOTE: RESURFACE TERRAZZO IN ACCORDANCE WITH NTMA SPECIFICATIONS.

  1. 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:
    1. For small areas, sand surface with a hand sander or small grinding tool, using fine stones to achieve desired finish. For larger areas (such as floors), use a circular buffing machine with grinding and polishing pads as recommended by NTMA.

      1. 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 #60 or finer grit stone/screen (or as recommended by NTMA).

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

      2. Rinse floor thoroughly with clean, clear water.
      3. Remove excess rinse water and machine or hand apply grout using identical Portland cement, 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 #60 or finer grit stone (or as recommended by NTMA), until grout has been removed from the terrazzo surface.

        CAUTION: TAKE CARE TO LIMIT GRINDING AND POLISHING TO A SMALL DISTANCE BEYOND THE DESIRED AREA.

      6. Wash surface with neutral cleaner and thoroughly rinse with clean, clear water. Allow the surface to thoroughly dry.
  2. Seal terrazzo with a penetrating type sealer as recommended by manufacturer.
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Last updated: Jul 24, 2025
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