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Historic Preservation - Technical Procedures

Spectitle:

Mortar Patching Holes In Stone Masonry

Procedure code:

0440003R

Source:

The Old Custom House, New York, Ny - Gsa/Pbs, 2/91

Division:

Masonry

Section:

Stonework

Last Modified:

06/27/2012

Details:

Mortar Patching Holes In Stone Masonry



MORTAR PATCHING HOLES IN STONE MASONRY


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on mortar patching holes
         in stone masonry where fastenings have been removed by
         other trades or damage has occurred for some other
         reason.

    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 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.   American Society for Testing and Materials (ASTM)
         www.astm.org
        


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Patching Mortar:

         1.   Portland cement: Type I, ASTM C150, white and/or
              gray as necessary to match mortar color to adjacent
              limestone color.

         2.   Hydrated masons lime: ASTM C207.

         3.   Aggregate:  Clean sharp sand free of loam, silt,
              soluble salts and organic matter.

              a.   For limestone, aggregate shall conform to the
                   following size gradations:

                   Sieve Size     Percent Passing

                   No. 4               100
                   No. 8               100
                   No. 16               97
                   No. 30               76
                   No. 50               17
                   No. 100               6
                   No. 200               0

              b.   For granite, aggregate shall conform to the
                   following size gradations:

                   Sieve Size          Percent Passing

                   No. 4                    100
                   No. 8                     97
                   No. 16                    85
                   No. 30                    65
                   No. 50                    28
                   No. 100                   13
                   No. 200                    2

                   Color and size of aggregate to match existing,
                   based on RHPO approval.

         4.   Clean, potable water

    C.   Anchor dowels, studs

    D.   Wire armature reinforcing - 16 gauge

    E.   Epoxy cement or grout

2.02 EQUIPMENT

    A.   Masonry drill

    B.   Stiff bristle brushes (non-metallic)

    C.   Steel trowel

    D.   Pneumatic or hand tools

2.03 MIXES

    A.   Proportions for Limestone Patching Mortar:

         1.   Portland cement: 1 part by volume

         2.   Lime: 2 parts by volume

         3.   Aggregate: 9 parts by volume

         4.   Water: to form a workable consistency

    B.   Proportions for Granite Patching Mortar:

         1.   Portland cement: 1 part by volume

         2.   Lime: 1 part by volume

         3.   Aggregate: 6 parts by volume

         4.   Water: to form a workable consistency

    C.   Mixing Procedures:

         1.   Measure materials by volume or equivalent weight.
              USE A KNOWN MEASURE.  DO NOT MEASURE BY SHOVEL.

         2.   Mix ingredients in clean mechanical batcher for 5-10 minutes.

         3.   Let mortar sit for 1 hour prior to use to allow for
              initial shrinkage.  Remix mortar to workable
              consistency.  Use mortar within 1.5 hours of
              initial remixing.  Discard left-over mortar.  DO
              NOT REMIX.


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

         1.   Prevent grout or mortar used in repointing and
              repair work from staining face of surrounding
              masonry and other surfaces.  Remove immediately
              grout and mortar in contact with exposed masonry
              and other surfaces.

         2.   Protect sills, ledges and projections from mortar
              droppings.

    B.   Surface Preparation:

         1.   Remove loose particles, soil, debris, oil and other
              contaminants from existing stone units at locations
              indicated by cleaning with stiff brush.

         2.   Prepare the patch substrate by carving with
              pneumatic stone working tools, "Barre" short stroke
              or by hand tools to make a clean surface, roughened
              to bond with patch material, and with edges at
              least 3/8-inch thick (1 cm), no feather edges, and
              undercut to provide a mechanical key for the patch.

3.02 ERECTION, INSTALLATION AND APPLICATION

    A.   Clean any exposed anchors of corrosion by scraping and
         brushing with stiff bristle brushes.  Replace any unsound
         anchors as necessary with new stainless steel anchors of
         same approximate size and shape.  Bed new anchors in
         epoxy grout.

    B.   Clean all stone areas to be patched of all debris, dust,
         oil, etc. by brushing with a stiff fiber bristle brush.

    C.   Provide mechanical keys or create wire reinforcing
         armature to hold and attach mortar patch.

    D.   Place patching mortar in layers no thicker than 1/2".
         Roughen surface of each layer to provide key for next.

    E.   Keep each layer damp for 72 hours or until mortar has
         set.

    F.   Dry pack and firmly compact patching mortar in the patch
         area, fully embedding reinforcing, free from voids, to
         fill the patch area slightly over full for smoothing and
         finishing when partially set.

    G.   Work and finish the patch when mortar has achieved its
         initial set and is firm, to match adjacent surfaces and
         finishes.

    H.   Form patches on edge of masonry units to restore the
         original unit's line and to maintain clear mortar joint
         lines, without bridging any mortar joint, so each stone
         unit is separate and not joined to the next one; joints
         to be filled by repointing, not mortar patches.

    I.   Unacceptable patches are defined as those with hairline
         cracks or showing separation from stone at edges.  Remove
         patches and refill to provide patches free of those
         defects.

                         END OF SECTION
 


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