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Historic Preservation - Technical Procedures

Spectitle:

Patching Spalled Limestone

Procedure code:

0446009R

Source:

National Capitol Region Specifications

Division:

Masonry

Section:

Limestone

Last Modified:

07/30/2013

Details:

Patching Spalled Limestone



PATCHING SPALLED LIMESTONE


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on repairing spalls in
         limestone using a cementitious patching material.

    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 SUBMITTALS

    A.   Sample Stone Repair:  Reattach stone fragments and patch
         stone at locations selected by the Contracting Officer's
         Representative using methods specified.  Provide one
         sample each for granite, limestone and marble.

PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Jahn Restoration Techniques and Research
         www.jahnmortars.com

2.02 MATERIALS

    A.   Cementitious patching material such as "M70 Stone
         Restoration Mortar" (Jahn Restoration), or approved
         equal; mixed and applied following manufacturer's guidance.

    B.   Clean, soft cloths

    C.   Clean, potable water

2.03 EQUIPMENT

    A.   Stiff natural bristle brush

    B.   Trowel

    C.   Chisel

    D.   Hammer

    E.   Putty knife


PART 3---EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

    A.   Cut back to sound stone with chisel and hammer.  Score
         surface to receive patch with chisel to provide a
         mechanical key with patching material. Undercutting if possible is recommended to hold patch more securely.

    B.   Thoroughly clean all stone dust and debris from areas
         that are to be repaired by air and then with a soft brush
         and water.

    C.   Pre-moisten stone with clean water and a stiff natural
         bristle brush to prevent patching mortar from drying out
         prematurely.  Avoid over wetting stone, which inhibits
         adhesion.  Prepare test patches as required for approval
         by the Contracting Officer's Representative to determine
         the correct degree of moistening.

    D.   First mix the cementitious patching material well in a
         dry state, then add water as per manufacturer's
         instructions, depending on the porosity of the limestone;
         between 150-200 cc of water to one kg of dry material.
         Patching mortar should be shapable without using molds
         and as it is being applied should hold its shape right
         away.  Do not mix more material than can be used within
         30 minutes.

    E.   Apply with trowel so that patch is slightly higher than
         adjacent surfaces.  Jahn Patching mortar can be put on
         from 3 mm to any required thickness at once.  Allow to
         harden for 7 days, then carefully cut back and tool to
         match adjacent surfaces.

                         END OF SECTION
 


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