Reinforcing Loose Terra Cotta Units And 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.

PREFACE: This procedure should be performed under the direction of an historical architect or engineer to determine the most efficient and least destructive manner for executing the work. Approval from the regional historic preservation officer is required.



  1. This procedure includes guidance on installing bent wire armatures or studs in terra cotta to additionally reinforce and anchor existing patches that are more than 1/2" thick, or any patch which is approximately fist size.
  2. This procedure requires substantial intervention and is only to be used to secure large patches to alreadydamaged terra cotta surfaces. If not properly anchored, large patches are particularly vulnerable to failure and separation due to weight, thermal expansion and bond failures.
  3. See "General Project Guidelines" 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. Sika Corporation
  2. Abatron, Inc.


  1. Stainless steel or bronze wire armature, or threaded rods and bolts. Threaded rods shall be sized according to the need and loading requirements. Consult with structural engineer and RHPO.
    1. Wire shall be 12-gauge or heavier.
    2. Stainless steel shall be AISI Type 316.
    3. The use of a wire armature or threaded rods shall be determined by size, depth and thickness of patch being stabilized. To be determined by structural engineer and RHPO.
  2. Moisture insensitive, structural epoxy or polyester resin adhesive as recommended by adhesive manufacturer (Sika Corporation, Abatron, Inc., or approved equal).
  3. Acrylic-cement finish.


  1. Masonry drill with diamond tipped coring bits.
  2. Electric drill with mixing paddle to pre-mix epoxy adhesive.
  3. Clean pail in which to mix epoxy adhesive.
  4. Pressure-injection equipment as may be required.
  5. Mixing nozzle: As recommended by adhesive manufacturer, the resin components may be automatically mixed by a nozzle that is secured to the component cartridges.



  1. Holes:
    1. The drill holes should be sized according to the wire or rod used. Typically, the hole shall be no greater in diameter than 1/8-inch or 1/4-inch (depending on the adhesive used) larger than the pin to be embedded, and ten to fifteen bar diameters deep.
    2. Drill shall be non-impact type rotary drill with a masonry bit.
    3. Depth of hole shall be sufficient to reach sound backing material.
    4. Space wire armature reinforcing at approximately 2-inches on center, arranged in a grid or mesh where applicable, or as recommended by structural engineer.
    5. Clean holes with high pressure air.
  2. Protection: Protect surfaces around holes from contact with adhesives. Use petroleum jelly, modeling clay or polyethylene sheets as required.
  3. Installation:
    1. Verify the rod length as appropriate for the depth.
    2. If using automatic pressure-injection equipment, resin shall be automatically measured and mixed in the mixing nozzle.
    3. If mixing by hand, mix each component by volume as directed by manufacturer into clean pail. Components shall be used straight, without any additives. Mix thoroughly for time specified by manufacturer with low-speed drill (400-600 rpm) fitted with appropriate paddle. Blend until uniform color is achieved.
    4. Pack or place the resin into holes.
    5. Slowly insert the wire armature or threaded rod into the resin to the full depth of the hole. Countersink head of rods.
    6. Do not disturb the anchor until the adhesive has cured. Follow manufacturers instructions.
    7. No gaps shall be visible between the rod and the masonry.
  4. Plug counter-sunk holes and build-out face of damaged patches as required flush with surrounding surfaces using patching mortar as described in HBPP procedure "Patching Small Holes, Minor Chips and Spalls in Terra Cotta".


  1. Immediately remove spills and excess adhesive with absorbent material and flush with water.
  2. Uncured material can be removed with solvent as recommended by adhesive manufacturer.
  3. Do not allow excess material to cure as cured adhesive can only be removed mechanically.


  1. Apply one coat colored masonry acrylic-cement finish to protect and repair damaged surface areas.
  2. Apply this protective, coloring, coating to existing old patch areas where the color does not match the terra cotta.