Concrete is a strong building material, but over time as the ground settles, it can develop cracks. Fortunately, repairing cracked concrete is a task even the most inexperienced do-it-yourselfer can tackle. Let’s patch that crack.
Evaluate the source
Before starting, consider where the crack is, what caused it and its characteristics.
Did the cracked concrete appear on your house’s foundation? If so, does it extend into the brick or masonry above the foundation? Is water present in the crack? If you patched the crack, did it reopen later? Each of these signs indicates a structural problem that a foundation repair professional should evaluate.
If the cracked concrete is on a sidewalk or driveway, how wide is it? Are the sides of the crack level with each other, or is one side higher than the other? The answer to these questions determines your repair approach. If the sides of the crack are even with each other, you can repair it. If one side is higher than the other, the only solution is to demolish the concrete and replace it.
Repairing hairline cracks
No matter how big the crack, it must be clean for an effective repair. Use a wire brush to clean small cracks of loose material. Follow up by vacuuming the crack to remove debris.
Fill the hairline crack with mortar repair filler that comes in a caulking tube. Squeeze the filler into the crack, wiping away the excess with your finger or a trowel as you go. When done, wipe away the overfill on each side with a cloth, then feather the area with a paint brush dipped in mineral spirits. After a few minutes examine the cracked concrete to see if the filler has settled unevenly. If any spots need additional fill, add it.
After the filler has cured completely, apply concrete sealer to the crack and the surface on either side to prevent moisture infiltration.
Repairing wider cracks
If a crack is a fourth-of-an-inch wide or wider, use a hammer and a chisel inserted down into the cracked concrete to chip the interior of the crack. You want to form an upside down “V”, so that the crack is wider underneath than at the surface. This is called “keying” and gives the filler a more stable setting in which to set up.
If the crack is deep, push foam filler backing rods into the crack along its length to provide a base for the patch material to rest upon. You can push these soft foam tubes down into the crack with a screwdriver.
For wider cracks, use concrete patch or an epoxy mix patch material. Trowel the patch material into the crack and smooth it down. Immediately wipe away the overfill on each side with the trowel and then with a cloth.
As with hairline cracks, after the material has cured, seal the cracked concrete and the immediate area around it to prevent water from seeping into the repair.