Historic Preservation - Technical Procedures
Patching Masonry Cracks
Hspg Prepared For Nps - Sero
Patching Masonry Cracks
PATCHING MASONRY CRACKS
A. This procedure includes guidance on patching cracks in
NOTE: THIS PROCEDURE SHOULD NOT BE USED IN THE JOINTS.
IT IS ONLY INTENDED FOR THE REPAIR OF CRACKS IN THE UNITS
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
C. Inactive cracks may be patched with an adhesive grout.
STRUCTURAL CRACKS SHOULD BE EXAMINED BY A STRUCTURAL
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:
1. Safety Precautions
2. Historic Structures Precautions
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).
A. Mameco, International
B. Sika Chemical
201 Polito Ave.
Lyndhurst, NJ 07071
C. Thoro System Products
7800 NW 38 Street
Miami, FL 33166
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
Flexible caulking or sealant:
1. For Interior Cracks: Butyl rubber caulk
2. For Exterior Cracks: One-part polyurethane caulk
such as "Vulkem #116" (Mameco, Int.), "Sikaflex
Multi-Caulk" (Sika Corp.), or approved equal.
B. Backer rod such as "Ethafoam" (available at builder's
supply houses or concrete materials suppliers), or
C. Clean, potable water
A. Hacksaw Blade
C. Hand-held Water Bottle
D. Steel Trowel
E. Caulking gun
F. Stiff bristle brushes (non-metallic)
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
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
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
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