How to Fill a Crack in a Basement Concrete Floor

Concrete foundations can sustain damage that may result in cracks in your basement's floor. While filling the crack is a very simple fix, you'll want to  take stock of where the crack is originating to ensure that further damage isn't being done. Simple settling isn't much of an issue, but tree roots or a faulty foundation may be. Though the tools you'll need to use are not specialized, they may not be part of your toolkit and will need to be purchased at the local home improvement store. For an extremely large crack, the same process can be used except you'll have to pour sand into the crack, followed by concrete and concrete fortifier.

Step 1—Chiseling

The crack needs to be chiseled out leaving a backward slope. That is interior recess of the crack should be larger than the surface crack. This allows for the patching compound to hold the crack in place and really seal it. By undercutting the interior, the patching compound can really set alleviating further damages.

Step 2—Loose Material

Using the wire brush, scrape away all loose material from the crack and the surrounding area. In order for the compound to seal the remaining walls of the concrete, it must have a solid surface to adhere to. A portable drill with wheel wire wheel attachment can also be used.

Step 3—Bonding

Use the paintbrush to apply a thin layer of bonding adhesive to the entire area around the crack. The bonding adhesive should also be applied to the upper interior of the crack. This holds the smaller particles together so they do not begin to separate and fall out of the crack. The bonding adhesive also helps to adhere the patching compound to the sides of the crack. Allow the bonding adhesive to completely dry before applying the patching compound.

Step 4—Patching Compound

Use a trowel to fully stuff the crack. The crack should be completely filled and air bubbles removed. In order to remove the air, stab at the concrete with the edge of the trowel to apply pressure and pop bubbles. After filling, be sure at least 1 inch of vinyl patching compound sticks up and out of the crack. Smooth this inch to a layer around the sides of the crack.

Step 5—Smoothing Out

Also called feathering, smoothing the crack to be level with the floors is not completely necessary. However, the smoothly feathered edge provides much easier movement in the area and eliminates a safety hazard. Use extra vinyl patching compound to apply around the edges of the crack at least 8 inches on both sides. Gradually smooth the compound from the crack and out to the 8 inch sides. This added compound not only removes the bulge from the patched crack, but can provide some added support so the crack doesn't split around itself later.