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Historic Preservation - Technical Procedures

Spectitle:

Patching Masonry Cracks

Procedure code:

0420003R

Source:

Hspg Prepared For Nps - Sero

Division:

Masonry

Section:

Unit Masonry

Last Modified:

02/24/2012

Details:

Patching Masonry Cracks



PATCHING MASONRY CRACKS


PART 1---GENERAL

1.01 SUMMARY

    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:

         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).


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Mameco, International
         Cleveland, OH
         216/752-4400

    B.   Sika Chemical
         201 Polito Ave.
         Lyndhurst, NJ  07071
         201/933-8800

    C.   Thoro System Products
         7800 NW 38 Street
         Miami, FL  33166
         305/597-8100

2.02 MATERIALS

    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.

         -OR-

         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
         approved equal.

    C.   Clean, potable water

2.03 EQUIPMENT

    A.   Hacksaw Blade

    B.   Chisels

    C.   Hand-held Water Bottle

    D.   Steel Trowel

    E.   Caulking gun

    F.   Stiff bristle brushes (non-metallic)


PART 3---EXECUTION

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