Installing a New Bonded Terrazzo Floor to Match Historic Terrazzo

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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.

Installing a New Bonded Terrazzo Floor to Match Historic Terrazzo






A. This procedure includes guidance on installing new bonded terrazzo to replace lost or severely damaged portions of existing terrazzo floors, or to enlarge or alter an area of existing/historic terrazzo floors. GENERALLY, THIS WORK SHOULD BE ACCOMPLISHED BY AN EXPERIENCED CONTRACTOR.


B. Characteristics of Terrazzo:


1. Good terrazzo has a smooth surface that is a mixture of 70% or more coarse aggregate and 30% or less portland cement matrix.


2. Terrazzo combines the durability of marble with the strength and economy of concrete.


3. Ease of maintenance is one of the principal reasons why terrazzo is found in so many buildings where traffic is heavy.


4. Pre-cast terrazzo tiles may be available for installation on all grade levels and over any sound subfloor construction; Typical sizes are 8, 12, and 16 inches square.


C. 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 prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).




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


B. NTMA has materials and installation tips in their SWEET's advertisement. Tips include:


1. Wax and sealant for required finish.


2. Abrasive strips added to finish at stairs, ramps, etc.






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 required color.


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


B. Sand: ASTM C33


C. Water: Clean, free of oil, soluble salts or other deleterious substances.


D. Aggregate: Natural, sound, crushed marble chips without excessive flats or flakes, complying with NTMA requirements. When matching existing terrazzo, the original aggregate types and ratios are often found listed on original drawings.


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


2. Aggregate colors and matrix pigments 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. Divider Strips in new spaces (not requiring restoration): Depth and style required for terrazzo type and thickness. Divider strips should be of solid composition and match existing (size, color, material). Materials may be brass, zinc... Do not use coated divider strips.


1. 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. NOTE: Use conventional terrazzo grinding equipment rather than lighter type machines.


H. Accessory Strips: Match width, material and color of divider strips, unless otherwise required. Provide following types of accessory strips as required for complete installation.


1. Control Joint Strips: 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.


I. Adhesive Bonding Agent: Epoxy or polyester resin.


2.02 MIXES


A. Underbed: One part portland cement to 4-1/2 parts sand and sufficient water to provide workability at as low a slump as possible.


B. Terrazzo Topping: One 94 pound bag of portland cement as per 200 pounds of marble chips and approximately 5 gallons of water.


1. Add color pigment as required to match existing color. Do not exceed, however, 2 pounds of pigment per bag of cement.







A. Examine the terrazzo to determine the type of terrazzo topping used. Match marble chips and matrix for existing terrazzo by size, mineral content and color. See Submittals. Color samples should be taken after cleaning.


B. Perform a thorough examination of the existing conditions. Perform any necessary tests on an inconspicuous surface to determine the current conditions and appropriate steps and materials necessary for replication and replacement of select areas of existing terrazzo surfaces.




A. Surface Preparation:


1. Clean and prepare substrate to comply with NTMA specifications for type of terrazzo application indicated. Clean substrate of loose chips and foreign matter. Grind concrete substrate to provide surfaces within tolerances required by NTMA for type of terrazzo application.


2. For cementitious terrazzo, comply with NTMA recommendations for proportioning mixes, installation of strips, and for placing, curing, grinding, grouting and finishing.


3. Thin-set Terrazzo:


a. Comply with NTMA guide specifications previously referenced under "Thin-set Terrazzo Materials" and with matrix manufacturer's directions for installing and finishing thin-set terrazzo. Match Contracting Officer's sample and provide total material thickness indicated. Sample should be taken after cleaning or from core sample of existing terrazzo.


b. Exercise extreme care to ensure fluids from grinding operation do not react with divider or control joint strips to produce a stain on aggregate or discolor strips.


c. Delay grinding and finishing until heavy trade work is completed and construction traffic through the area is restricted.


4. Provide terrazzo bases, thresholds, stair treads and landings, without interruptions of seams, except where divider strips, control joints and expansion joints are required. Place and finish terrazzo around obstructions to achieve continuous color, pattern and finish.


5. Provide control joints where required by installing angle-type divider strips back-to-back with neoprene rubber filler cemented between strips, flush with finish floor.




A. Match the historic character and pattern of the terrazzo in all spaces containing or contiguous with existing terrazzo.


B. Sand Cushion (floating) Terrazzo: Comply with NTMA "Guide Specification for Bonded Terrazzo".


1. Used where structural movement is anticipated from settling, expansion, contraction, or vibration, which may cause injury to the terrazzo topping;


2. The overall thickness of the underbed and topping needs to be at least 3 inches.


3. The concrete slab is covered with a thin bed of dry sand, over which is laid a waterproof membrane and reinforcing wire mesh.


4. Install the terrazzo underbed to 5/8 inch below the finished floor line.


5. Place divider strips and then pour terrazzo topping.


C. Bonded-to-Concrete Terrazzo: Comply with NTMA "Guide Specification for Bonded Terrazzo".


1. Used in all general areas-corridors, lobbies, rooms, sidewalks, etc.


2. The minimum overall thickness (most common) is 1-3/4 inches; With reinforcing, 2 or 2-1/2 inches is appropriate.


3. Thoroughly clean and soak the base slab with water.


4. Slush it with dry portland cement to ensure a good bond.


5. Install the underbed followed by the placing of divider strips and terrazzo topping.


D. Monolithic Terrazzo: Installed at 5/8 inch thick, it is bonded to or made integral with the prepared slab.


E. Thin Terrazzo Toppings: Installed at 3/8 inch thick on concrete slab which has first been covered with adhesive bonding agent, i.e., polysulfide liquid polymer.


F. Terrazzo-over-Wood:


1. Floor must be structurally sound and rigid.


2. Lay waterproof membrane such as 15-lb. roofing felt or plastic sheeting.


3. Lay reinforcing wire mesh over membrane.


4. Spread 2" thick underbed of cement and sand.


5. Lay 5/8" topping.


G. Surfacing: Grout cured terrazzo topping in accordance with NTMA specifications.


1. Delay grinding and finishing until heavy trade work is completed and construction traffic through the area is restricted.


2. Finish by fine grinding with abrasive grit of size specified by NTMA, or as otherwise required to match original intact material.


3. Grind and polish the new areas, patches, and the entire floor as required to produce a clean, smooth, and uniform finish, capable of being sealed and polished to match the original installation.




4. Cover with vapor barrier sheets to prevent quick hydration.




A. Keep terrazzo free of acids and oils.


B. Protect the floor, especially the grouting, with a penetrating type seal.


C. Daily Cleaning:


1. Daily sweeping with a cotton-wick floor brush, treated with a non-oily dressing, will control dust and make maintenance easier.


2. Regular damp-mopping keeps the surface free from dirt accumulations.


D. Periodic Cleaning:


1. Machine buffing on a regular basis removes traffic marks and restores luster.


2. Touching up with sealer in traffic areas as needed protects the surface.


3. Periodic machine scrubbing removes heavy accumulations of dirt.


4. Seal and wax as needed.


5. Use a penetrating type terrazzo seal.


6. Avoid seals which may turn yellow and discolor.


7. Normal stripping and buffing procedures are suitable.


C. Clean terrazzo after installation and finishing operations are completed, complying with sealer manufacturer's instructions.


D. Apply sealer to cleaned terrazzo surfaces to comply with sealer manufacturer's instructions.


E. Protect terrazzo from damage and wear during construction operation.