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Historic Preservation - Technical Procedures

Spectitle:

Patching Minor Chips And Cracks In Terrazzo With Cement Grout

Procedure code:

0940003R

Source:

J. Weinberger Us Cthouse/San Diego, Ca - Hallenbeck Chamorro

Division:

Finishes

Section:

Terrazzo

Last Modified:

02/24/2012

Details:

Patching Minor Chips And Cracks In Terrazzo With Cement Grout



PATCHING MINOR CHIPS AND CRACKS IN TERRAZZO WITH CEMENT GROUT


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on repairing small
         cracks in terrazzo floors by patching with cement grout.

    B.   Minor chips and cracking in terrazzo require patching
         ONLY when surface irregularities present safety hazards
         or when it is necessary to prevent further deterioration
         to the terrazzo.

    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).

1.02 REFERENCES

    A.   NTMA Standards:  Comply with specified provisions and
         recommendations of the 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.


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 non-staining 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 7 and
         10, that does not affect color or physical properties of
         terrazzo surface.

    I.   Plastic Sheeting

2.02 EQUIPMENT

    A.   Grinding Stones:  Fine grit emery stones manufactured
         specifically for restorative type grinding and surfacing
         of terrazzo surfaces (#40 and #80 grit stones).

    B.   Power Saw and Hand Tools

    C.   Resurfacing Screens:  A fine grit screen manufactured
         specifically for restorative type grinding and
         resurfacing terrazzo surfaces.

         
PART 3---EXECUTION

3.01 PREPARATION

    A.   Surface Preparation:

         1.   With a power saw or hand tools, cut a vertical
              perimeter wall around the area to be patched.  If
              the patch is smaller than an inch square, slightly
              undercut this edge.  

         2.   Clean surface of debris.  Saturate void with water
              to prevent quick surface drying.  Ensure that water
              penetrates into the surface in order to achieve a
              proper bond.  Clean surfaces until any obstructing
              material has been removed.  

         3.   Apply cement paste and work into the surface.  Do
              not allow cement paste to dry before placing
              terrazzo composition.

3.02 ERECTION, INSTALLATION AND APPLICATION

    NOTE:  Match marble chips and matrix for existing terrazzo by
    size, mineral content and color.  Colors should be matched
    after cleaning or taken from the interior of core samples
    depending upon scope of work.

    A.   Mix two parts blended marble chips with one part Portland
         Cement and add enough water to make this mix plastic.

    B.   Place mixture over chip or crack and level with a trowel.

    C.   Seed additional marble chips of the same blend over the
         patch, as required to establish a uniform coverage.

    D.   Compact patch, removing all excess water and cement from
         the surface.

    E.   Cover the patch with paper or polyethylene sheeting to
         prevent quick hydration.  Cure until topping develops
         sufficient strength to prevent lifting or pulling of
         terrazzo chips during grinding.  

    F.   Sand surface with a hand sander or small grinding tool,
         using fine stones to achieve desired finish.

         1.   Use a #40 or finer grit stone for the initial
              grinding, exposing the marble chips.  Follow with a
              fine #80 grit stone before grouting with cement to
              fill all pinholes.  

              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.   Cover grouted surface with paper or polyethylene
              for at least 72 hours.

         3.   Thoroughly rinse the surface with clean, clear
              water.

         4.   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.

         5.   Final polish with a #80 or finer grit stone.  Care
              should be taken to limit grinding and polishing to
              a small distance beyond the perimeter of the patch.
             
    G.   Seal patch with a penetrating type terrazzo sealer.

                             END OF SECTION