Patching Masonry Cracks
- Procedure code:
- HSPG Prepared For NPS - Southeast Regional Office
- Unit Masonry
- Last Modified:
PATCHING MASONRY CRACKS
A. This procedure includes guidance on patching cracks in masonry. NOTE: THIS PROCEDURE SHOULD NOT BE USED IN THE JOINTS. IT IS ONLY INTENDED FOR THE REPAIR OF CRACKS IN THE UNITS THEMSELVES.
B. Active cracks caused by thermal expansion may be patched by injecting a caulk or sealant. Thermal expansion cracks are those which open and close with the change in seasons. These types of cracks must be allowed to move along with normal movement of the building, while at the same time exclude moisture penetration.
NOTE: CRACKS SHOULD ONLY BE CAULKED IF ACTIVE AND/OR OF SUFFICIENT WIDTH. HAIRLINE FRACTURES USUALLY NEED NO CAULKING.
C. Inactive cracks may be patched with an adhesive grout. STRUCTURAL CRACKS SHOULD BE EXAMINED BY A STRUCTURAL ENGINEER.
D. Masonry buildings without adequate expansion joints may be subject to structural cracking in areas of stress. In some cases, an expansion joint or multiple ones may be required to be retrofitted. This is a major design issue and beyond the scope of this procedure. Consult experienced structural engineers where questions exist over appropriate treatment. Cracks may be serious and should be evaluated to determine if they are active and what the structural implications are. For guidance on monitoring cracks in masonry, see 04200-02-S.
E. 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).
PART 2---PRODUCTS 2.01 MANUFACTURERS A. Tremco Commercial Sealants and Waterproofing http://www.tremcosealants.com/
B. Sika Corporation http://usa.sika.com/
C. Thoro System Products http://www.thorosystem.com/
A. Low pressure injectable cement-sand acrylic modified grout for masonry crack repairing (Thoro System Products), or approved equal; To match masonry finish with consistency for hand tool or caulking gun placing as required.
Flexible caulking or sealant:
1. For Interior Cracks: Butyl rubber caulk
2. For Exterior Cracks: One-part polyurethane caulk such as "Vulkem #116" (Tremco), "Sikaflex
1A" (Sika Corp.), or approved equal.
B. Backer rod such as "Ethafoam" (available at builder's supply houses or concrete materials suppliers), or approved equal.
C. Clean, potable water 2.03 EQUIPMENT
A. Hacksaw Blade
C. Hand-held Water Bottle
D. Steel Trowel
E. Caulking gun
F. Stiff bristle brushes (non-metallic)
3.01 EXAMINATION A. Evaluate alternative methods of repair and determine possible consequences if left unrepaired. 3.02 ERECTION, INSTALLATION, APPLICATION
A. Clean out the crack of any loose dust and debris using a stiff bristle brush or by blowing air into the crack.
B. Widen the crack as necessary using appropriate hand tools.
C. For Active Cracks:
1. For cracks determined to move at least 1/8 inch, the joint should be at least 1/2 inch wide. A sealant can move 25% of its width. The depth of the sealant must be at least 50% of the joint width.
2. For joints 3/8 inch or wider, insert a closed-cell polyurethane backer rod.
3. Push the backer rod into the joint to fill up the space behind the sealant.
4. Fill existing crack with a flexible caulking or sealant. Apply with a caulking gun until flush with the surface.
D. For Inactive cracks not associated with structural movement:
1. Fill crack with adhesive grout using repointing tools or a caulking gun.
2. Force grout deep into joint to firmly anchor adjoining surfaces and prevent the entry of pests and weathering elements.
E. For Structural Cracks: Consult a structural engineer.
END OF SECTION