Patching Chips And Cracks In Ornamental Concrete Block

CSI Division
Division 4- Masonry
Section
Concrete Unit Masonry
Last Modified

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.

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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.

PART 1–GENERAL

1.01 SUMMARY

  1. This procedure includes guidance on repairing chips, cracks or holes in ornamental concrete block. Small areas may be patched using a mortar mixture; larger areas may require pins and mortar for additional reinforcement.
  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).

1.02 REFERENCES

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

1.03 PROJECT/SITE CONDITIONS

  1. Environmental Requirements:
    1. Check manufacturer’s literature for precautions and effects of products and procedures on adjacent building materials, components, and especially vegetation; Take appropriate protective measures as necessary.
    2. Wet Weather: Do not apply or mix mortar on outside surfaces with standing water or outside during rain.
    3. Do not proceed with patching under adverse weather conditions, or when temperatures are below or above manufacturer’s recommended limitations for installation; Proceed with the work only when forecasted weather conditions are favorable for proper cure.
    4. Cold Weather, winter construction is not allowed without consent of Regional Architect; Winter construction is defined as any time when surface temperature of masonry is below 50 degrees F. or air temperature is predicted to be below 40 degrees F. within 48 hours; Heat mortar materials to above 50 degrees F. if necessary.
    5. Work must not be done at temperatures above 80 degrees F. unless shading and water-misted burlap over new work is provided. Mortar mixing should be done only in the shade; cover mortar in hot weather to reduce evaporation. Pointing work should be done in the shade. Work around the building during the day so that the fresh work will be shielded from direct sunlight to reduce evaporation rate.

PART 2–PRODUCTS

2.01 MATERIALS

  1. Clean, potable water
  2. Portland cement
  3. Hydrated lime
  4. Sand
  5. Epoxy cement
  6. Teflon or nylon pins with scored and threaded surface. (Stainless steel or bronze may be used if teflon or nylon are unavailable).

2.02 EQUIPMENT

  1. Stiff bristle brushes or vacuum
  2. Trowels
  3. Hawks
  4. Carbon-tipped masonry bit

PART 3–EXECUTION

3.01 ERECTION, INSTALLATION, APPLICATION

  1. Patching small cracks and holes with grout (a wetter version of mortar mix):
    1. Cut out the deteriorated area to a sound surface. Under-cut the edge where possible to create a “key”.
    2. Brush or vacuum out all dirt or debris.
    3. Flush the area with clean, clear water. Be sure no standing water remains.
    4. Mix 1 part Portland cement, ASTM C150, Type I, part hydrated lime, and 2 to 3 parts sand
      -OR-
      1 part Portland cement Type P (lime pre-mixed), and 2 to 3 parts sand
      NOTE: ADJUST MIX TO MATCH COLOR, TEXTURE AND PHYSICAL PROPERTIES OF THE ORIGINAL MORTAR.
    5. Thin mortar to a slushy batter consistency.
    6. Trowel apply mortar to damaged area in layers no more than 1 inch thick. Several layers may be required. DO NOT APPLY PATCHES OVER JOINTS.
  2. Patching large chips, holes or broken corners using pins and mortar:
    1. Using a stiff bristle brush, clean surfaces to be joined or patched.
    2. Using a carbon-tipped masonry bit, drill staggered rows of holes approximately 2 inches deep (no more than 4 times the pin diameter), 1-1/2 inch apart and 1/8 inch wider than the pin diameter.
    3. Again, brush debris from the surface.
    4. Fill the holes with mortar mix or epoxy cement.
    5. Set the pins in the holes.
    6. Trowel apply mortar to damaged area in layers no more than 1 inch thick. Several layers may be required. DO NOT APPLY PATCHES OVER JOINTS.
    7. To patch a chipped corner, fill the cavity with the concrete mix or bonding material, forcing it in and around the exposed pins, which will act to support and reinforce the patch.
  3. To rejoin two broken parts (such as a concrete baluster), coat both broken surfaces with epoxy adhesive and gently tap the parts together.

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Last updated: Aug 13, 2017
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