Repairing cracks in a concrete wall is a simple procedure that can usually be completed within a day or so. Cracks that form in a concrete wall, particularly a basement wall due to settlement, frost heave, or ground movement can be either structural or non-structural. The methods discussed in this article can be used to repair minor, non-structural cracks.
Step 1 - Clean and Prepare the Cracked Area
Before you start to repair the crack, use any combination of a wire brush, vacuum, or power washer to remove any oil, dirt, or debris from the concrete wall surface and from inside the crack. The crack must be prepared so that the sealant will adhere to the crack surfaces. Do this by enlarging the crack using a concrete chisel and a hammer. Holding the chisel at an angle within the crack, chisel down to a depth of about 1 inch along the entire length of the crack. Reverse the angle and repeat the procedure. The objective is to create an inverted V shape below the surface, otherwise known as undercutting. The chiseled surface provides a stronger bond with the sealant and the diverging angle of the crack helps keep the sealant within the crack. Remove all loose material and dust from the inside of the crack.
Step 2 - Patch the Concrete
There are many products available that can be used to fill and seal the crack including pre-mixed concrete. If you are using concrete to “patch” the crack, apply masonry adhesive or some type of bonding agent to the inner surface of the crack. Then trowel the concrete into the crack until it is completely filled; don’t leave a depression along the surface of the patch. Use a trowel, float, brush, or broom to match the texture of the adjacent concrete finish.
Step 3 - Add Manufactured Sealants
Other types of sealant work well for filling cracks. Epoxy products can be used to fill cracks up to ½ inch wide, but will not bond to wet or “green” concrete. Epoxy is typically purchased as two separate compounds that are mixed together at the proper ratio. It creates a semi-rigid bond with strength properties greater than the concrete itself. Consult the manufacturer’s instructions on the proper procedure for mixing, applying, and curing the epoxy. Epoxy-based grouts are an option if no further expansion of the crack is expected. The material provides a rigid bond that will not accommodate additional movement within the concrete.
Expandable polyurethane is a water-resistant foam sealant that also can be used to fill cracks up to ½ inch wide. It creates a flexible bond that will allow for minor shifts and ground movements. It is injected into the crack under high pressure so that entire cavity is sure to be filled.
Hydraulic cement and caulking are generally not recommended for repairing cracks in concrete. Hydraulic cement is a rigid material that will not bond well to concrete. Caulking is flexible but does not provide a permanent bond. Neither is impervious to water.