How to Repair Cracks in a Concrete Slab Foundation

A crack in a concrete slab foundation.
  • 2-3 hours
  • Intermediate
  • 300-400
What You'll Need
Wire brush
Garden hose
Concrete patching compound
Putty knife
Concrete bonding adhesive
Putty knife

A concrete slab foundation is a common installation in many homes. Concrete is one of the toughest materials available for construction. It creates a solid and durable foundation. Cracks are common in concrete foundations. They are often caused by weather conditions and poor drainage. It is best to repair cracks as soon as you spot them. If unattended, cracks can grow extensively and necessitate costly repair. Delayed repairs can also allow leakage and entry of radon gas into your home. It helps if you know how to repair cracks in a concrete slab foundation.

Step 1 - Inspect

Carefully inspect your concrete foundation so that you can identify cracked areas. This way, you can undertake repairs of all the cracks at one go. It helps to fortify your concrete foundation. Use chalk to mark the faulty areas. You may want to use a different color to identify small cracks and mark the large cracks with another color. This is because they require different treatments.

Step 2 - Chisel out the Crack

Use a chisel to chip away the loose concrete within the crack. This will ensure that you are clear as much of the weakened concrete as possible. The concrete filler bonds more effectively when placed within a compact area.

Step 3 - Scrape

Scour the crack with a wire brush to remove the loose concrete and debris. It is important that you have a clean site before you pour in the concrete filler. The presence of loose concrete and debris weakens the composition of the filler. It also prevents a secure bond between the filler and the solid concrete.

Step 4 - Rinse

To effectively clean out the crack, you’ll need to flush with water. Use your garden hose to rinse the crack thoroughly. Allow the area to dry completely.

Step 5 - Hairline Cracks

Use a paintbrush to spread a thin layer of concrete bonding adhesive to the repair area. The adhesive helps to bind the repair material so that it doesn’t pop out of the crack once it dries. Mix some concrete patching compound and fill the crack with this. Use a putty knife to feather the edges of the crack so that it is similar to the adjacent areas. Allow the crack to dry completely before you walk on it.

Step 6 - Large Cracks

Pour sand into the crack to reduce its depth. The crack should not be more than 3 inches deep. Use a paintbrush to apply some concrete bonding adhesive inside the crack as well as on both edges at the surface. Prepare some concrete patching compound and fill the crack. Be sure to compact the concrete mix within the crack so that it seals more effectively. Use a trowel to feather the concrete mix at the surface for a uniform appearance. Be sure the area has dried completely before you allow any foot traffic on it.


If your concrete foundation has several cracks, you may want to resurface after repairs are completed. This will give you a more solid and secure foundation.