Repairing Cracks in Concrete Basement Floors

Using Concrete Fillers to Repair Cracks in Concrete Basement Floors

By Mark J. Donovan

Over time most concrete basement floors exhibit small cracks. Fortunately, repairing cracks in concrete basement floors is a project most do it yourself homeowners can undertake. With any luck a homeowner can repair a crack in as little as one or two hours.

Even when a foundation contractor does all the right things prior to pouring the concrete basement floor, such as installing plenty of gravel, rebar, and reinforcing wire, basement floors still tend to get minor cracks over time.

The cracks form due to the home settling and water running under the basement floor. Over time, the water washes away sand and gravel underneath sections of the concrete basement floor. Without the support of the sand and gravel, the concrete basement floor comes under pressure and cracks in the area where the sand and gravel washed away.

Repairing a crack in a concrete basement floor may not be necessary if there is no water seeping out of it. However, keep in mind water is likely flowing underneath the basement floor and by leaving the crack in disrepair you are allowing higher moisture levels to form in the basement. Higher moisture levels can translate into the formation of mold and mildew.

Repairing Hairline Cracks

For hairline cracks, where no signs of water infiltration are occurring, simply use a tube of concrete filler made out of epoxy, vinyl or latex, to make the patch.

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If the hairline crack exhibits signs of water infiltration you will need to use hydraulic cement. Hydraulic cement comes in a dry powder form. You simply add water, to the manufacturer’s recommendations, mix it up, and apply it to the hairline crack. Watch how to repair a concrete foundation crack in this video.

In either case, make sure you first clean the area well. The area should be completely free of dirt and oil or else the concrete filler will not adhere well to the concrete crack.

Repairing Larger Cracks

For larger cracks, you will first need to clean the area well of loose concrete pieces. Frequently you will need to use a hammer and chisel to remove these loose sections of concrete. Hold the chisel at a 45 degree angle while pounding it with a hammer.

Walk the length of the crack holding the chisel on this angle. This process is called “keying” and it helps to ensure a better bond with the crack and the patch / concrete filler.

Again, as with hairline cracks, after chiseling the crack, clean the area well. All dust and grease should be removed from the area prior to applying the concrete filler.

Note: Make sure you wear eye protection while chiseling the cracks as loose pieces can fly up.

Applying Concrete Filler

Once you have prepared the site (concrete crack), it is now time to apply the tube of concrete filler.

First, cut the tube at a 45 degree angle.

Next, apply the tube of concrete filler to the crack. Make sure you do this in a slow and methodical manner so that the crack is entirely filled as you move along its length.

Allow Concrete Filler to Setup

Allow the concrete filler to setup for a few minutes. Then inspect the crack to see if there are any sags, e.g. where the concrete filler might have settled. If you see any sagging, apply more concrete filler to the specific areas.

Trowel Concrete Filler

Once the crack has had a few minutes to setup, and you no longer observe any sagging, use a trowel to smooth and feather out the crack line.

Let the area rest overnight and check the next day to see if it has cured. Again, if there is any more sagging, apply more filler to the low areas, re-trowel and let rest overnight again.

Apply a Sealant to the Repaired Crack

Once the concrete filler has set up, you should apply a polyurethane sealant to the repaired crack to prevent any possible water vapor infiltration, and to prevent susceptibility to future staining. Concrete floors have the tendency to stain easily.

The polyurethane sealant can be applied with either a roller or a brush. For best protection apply 2 to 3 coats of the sealant.

Once the sealant has dried your concrete basement floor is as good as new!

For more help on Basement Additions, see’s Basement Remodeling Bid sheet. The Basement Remodeling Bid Sheet will help ensure that your hire the right contractor so that your basement remodeling project is done correctly and you get the project finished on time and budget.

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