Reattaching Loose Or Spalled Limestone
- CSI Division:
- Division 4- Masonry
- Last Modified:
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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.
A. This procedure includes guidance on reattaching loose or spalled limestone that is reusable and has not been extensively damaged.
B. See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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).
- American Society for Testing and Materials (ASTM), www.astm.org
- Axson Technologies (formerly Akemi Plastics, Inc.) www.axsontech.us
- Sika Corporation http://usa.sika.com
- Replacement limestone - reuse any loose or fallen stone fragments that are still sound; re-use such stone in its original position and location; replacement stone should match existing limestone in color, texture and type.
- Epoxy Adhesive such as "Sikadur 32 Hi Mod" epoxy adhesive, or approved equal (Sika Corporation).
- High modulus, high strength, moisture insensitive epoxy adhesive with a pot life of 30 minutes at 70 degrees F.
- Can be applied at temperatures as low as 40 degrees F.
- Colored to match existing limestone.
- A color-matched polyester-based adhesive such as "Limestone Super",(Wood & Stone Company, a Axson Technologies US, Inc. company), or approved equal.
- 10-12 minute cure depending on ambient temperature; temperatures below 32 degrees F (O degrees C) require heated mixture.
- Can be applied at temperatures as low as 20 degrees F
- Colored to match existing limestone.
- Permanent coloring agent as required, compatible with adhesive, and as recommended by adhesive manufacturer.
- Stainless steel rods for reinforcement: 1/4 inch diameter threaded rods, length as required.
- Stiff bristle brushes (natural fiber or nylon)
- Polyethylene plastic mixing vessel for mixing adhesives and patching mortar
3.01 ERECTION, INSTALLATION, APPLICATION
- Carefully remove all loose fragments of stone. Set aside all pieces in good condition for reuse.
- Clean exposed metal anchors. Remove corrosion by scraping with a stiff wire bristle brush.
- Remove unsound metal anchors and replace with new stainless steel anchors of similar size and shape. Bed anchors in epoxy grout.
- Remove dust and debris from building stone and fragments using a stiff bristle brush.
- For small fragments (.5 cubic feet or less):
- Coat building stone surface with adhesive such as noted above, or approved equal. Be sure to cover the entire surface, filling all voids.
- While adhesive is still tacky, set stone fragment in place. Prevent fragment from moving until adhesive is fully cured.
- Clean any residual adhesive from the stone surface using water and stiff bristle brush. Wet stone and fill any chips with lime-based patching mortar of appropriate color, texture and composition. Tool surface level with surrounding stone.
- For large fragments (more than 4 inches by 4 inches by 4 inches):
- Follow procedures in E.1. above.
- After adhesive has cured, anchor fragments with 1/4 inch smooth stainless steel rods.
- Drill 1/4 inch holes at a 45 degree downward angle through the face of the newly set stone fragment. Drill holes should extend at least 2 inches into the backing stone, 2 inches into the fragment and should allow for the rod to be countersunk at least 3/4 inches from the face of the stone.
- Space the anchor rods between 3 and 5 inches apart and no less than 2 inches from any edge.
- Clean any residual adhesive from the stone surface using water and a stiff bristle brush. Wet stone and fill holes from countersunk rods with patching mortar. Tool surface level with surrounding stone.