Cementitious Patch Repair Of Granite Spalls Or Failed Patches

Technical Procedures Disclaimer

Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.


We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.



  1. This procedure includes guidance on the removal and replacement of existing loose or deteriorated cementitious patches. For guidance on attaching small granite fragments using epoxy adhesive, see 04465-21-R.
  2. 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. Product Data: Submit manufacturer's product literature for epoxy adhesives or resins.
  2. Samples: Submit samples of dowels for patch anchorage.


  1. Environmental Requirements: No work in this section shall be performed when the ambient temperature is less than 40 degrees F and falling, or higher than 90 degrees F.
  2. Existing Conditions:
    1. The Contractor shall be responsible for the protection of all adjacent materials during the execution of the work.
    2. The Contractor shall repair all damage to adjacent materials caused by the execution of the work of this section at no expense to the Owner.



  1. Jahn Restoration Mortars www.cathedralstone.com
  2. Sika Corporation www.usa.sika.com


  1. Patch dowels: Threaded rods of A.I.S.I. Type 302/304 stainless steel, sizes as required.
  2. Cementitious patching material such as "M160 Granite and Bluestone Repair Mortar" (Jahn Restoration Mortar), or approved equal, through various vendors.
  3. Clean, soft cloths
  4. Clean, potable water
  5. Epoxy grout: High-modulus, low viscosity, high strength epoxy grouting/sealing/binder adhesive such as "Sikadur 35, Hi-Mod LV" (Sika Corporation), or approved equal.


  1. Stiff natural bristle brushes
  2. Stiff wire bristle brushes
  3. Trowel
  4. Chisel
  5. Hammer



  1. Temporarily remove and store light fixtures, mounting brackets, conduit, signs and other building accessories to facilitate the restoration work. Reinstall all removed items.


  1. Cut back to sound stone with chisel and hammer. Score surface to receive patch with chisel to provide a mechanical key with patching material.
  2. Thoroughly clean all stone dust and debris from areas that are to be repaired by air and then with a soft brush and water.
  3. Clean any exposed metal anchors of all corrosion by scraping and brushing with stiff wire brushes. Replace any unsound anchors as necessary with new stainless steel anchors of same approximate size and shape. Bed new anchors in epoxy grout.
  4. 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.
  5. First mix the cementitious patching material well in a dry state, then add water as per manufacturer's instructions. 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.
  6. Apply with trowel so that patch is slightly higher than adjacent surfaces. Jahn repair 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. Maintain mortar joints; do not install patch across joints.
  7. Keep patches damp for 72 hours after installations.