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Historic Preservation - Technical Procedures

Spectitle:
Regrinding Terrazzo Floors

Procedure code:
0940010R

Source:
Vitrification Floor Care For Terrazzo - Nilfisk Of America

Division:
Finishes

Section:
Terrazzo

Last Modified:
02/24/2012

Details:
Regrinding Terrazzo Floors



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.


PART 1---GENERAL

1.01 SUMMARY

    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

         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

    A.   NTMA Standards:  Comply with specified provisions and
         recommendations of National Terrazzo and Mosaic
         Association, Inc. (NTMA), 3166 Des Plaines Avenue, Ste.
         132, Des Plaines, IL  60018, 800/323-9736 or 708/635-
         7744, FAX (708) 635-9127.

    B.   ASTM Standards:  Comply with specified provisions and
         recommendations of American Society for Testing and
         Materials (ASTM), 100 Barr Drive, West Conshohocken, PA
         19428, (610) 832-9585 or FAX (610) 832-9555.


PART 2---PRODUCTS

2.01 MATERIALS

    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 nonstaining white cement for terrazzo
              matrix.

    B.   Sand:  ASTM C33

    C.   Clean, potable water

    D.   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
              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

2.02 EQUIPMENT

    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)

    G.   Sponges

    H.   Clean, dry cloths


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    NOTE:  RESURFACE TERRAZZO IN ACCORDANCE WITH NTMA
    SPECIFICATIONS.  

    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
                   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.

              b.   Rinse floor thoroughly with clean, clear
                   water.

              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
                   DESIRED AREA.  

              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.

                             END OF SECTION