Installing A New Bonded Terrazzo Floor To Match Historic Terrazzo

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




    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 2015-12-01