Installing A New Bonded Terrazzo Floor To Match Historic Terrazzo

Procedure code:
J.Weinberger US Cthouse/San Diego, CA - Hallenbeck, Chamorro
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    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



    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,







    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



    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



         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



    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



    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



              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



    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



    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



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


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



         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.  



              DIVIDER STRIPS (SEE 2.01 H.).


         4.   Cover with vapor barrier sheets to prevent quick





    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



    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



                             END OF SECTION


Last Reviewed 2017-03-13