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.
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.
REGRINDING TERRAZZO FLOORS
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.
A. 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.
B. 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
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.
A. NTMA Standards: Comply with specified provisions and
recommendations of National Terrazzo and Mosaic
Association, Inc. (NTMA), www.ntma.com
B. ASTM Standards: Comply with specified provisions and
recommendations of American Society for Testing and
Materials (ASTM), www.astm.org
A. Portland Cement: ASTM C150, Type I, except as modified
to comply with NTMA requirements for compressive
strength. Obtain cement from a single source for each
1. Provide nonstaining white cement for terrazzo
B. Sand: ASTM C33
C. Clean, potable water
D. Aggregate: Natural, sound, crushed marble chips without
excessive flats or flakes, complying with NTMA
1. Colors and gradation of aggregate sizes as required
to match original existing intact materials and
patterns. Original plans often contain the exact
2. Aggregate colors should be matched after cleaning
or taken from the interior of core samples
depending upon scope of work.
E. Matrix Pigments: Pure mineral or synthetic pigments,
resistant to alkalies and non-fading. Mix pigments with
matrix to provide required colors.
F. Curing Compound: Liquid-membrane-forming compound, ASTM
C309, Type 1.
G. Grout: A cement/acrylic grout with color added to match
the matrix of the original terrazzo.
H. 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.
I. Kraft paper or plastic sheeting
A. Hand sander, small grinding tools
B. Grinding Stones: Fine grit emery stones manufactured
specifically for restorative type grinding and surfacing
of terrazzo surfaces (#24 and #80 grit stones, or as
recommended by NTMA).
C. Resurfacing Screens: A fine grit screen manufactured
specifically for restorative type grinding and
resurfacing of terrazzo surfaces.
D. Soft natural bristle brushes
E. Circular buffing machine (for floors) with grinding and
polishing screens as recommended by NTMA. Use
conventional terrazzo grinding equipment rather than
lighter type machines.
F. Mop and bucket (non-metallic)
H. Clean, dry cloths
3.01 ERECTION, INSTALLATION, APPLICATION
NOTE: RESURFACE TERRAZZO IN ACCORDANCE WITH NTMA
A. 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.
a. 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
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.
b. Rinse floor thoroughly with clean, clear
c. 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.
d. Cover grouted surface with paper or
polyethylene for at least 72 hours.
e. Final polish with a #80 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
f. Wash surface with neutral cleaner and
thoroughly rinse with clean, clear water.
Allow the surface to thoroughly dry.
B. Seal terrazzo with a penetrating type sealer as
recommended by manufacturer.