How to Fix Cracks in Your Basement Floor

Concrete floors are used for basement floors almost exclusively. Because concrete shrinks as it dries, cracks sometimes form. As the house ages and the surrounding earth shifts naturally, sometimes these cracks can be widened and allow water to seep up through them. Products are available to aid in patching both small and large concrete floor cracks. As long as the floor and cracks are relatively clean, dry patching takes a very short time and will extend both the life and dryness of the basement considerably.

  • Broom
  • Small brush
  • Wire brush
  • De-greaser
  • Soap
  • Bucket
  • Sponge
  • Concrete filler
  • Trowel or putty knife
  • Concrete patching compound
Sweep the floor to remove any dirt or dust. For small cracks, use a small, soft brush to clean any debris from in and around the crack. For larger cracks, use a wire brush to break loose anything that may be lodged into it.

Use a de-greaser and soap and water solution with a sponge to clean the floor around the cracks to be filled, which is especially important for old concrete floors that may have deeply embedded grease and grime. Allow the floor to dry completely, especially the cracks.

For hairline cracks and cracks less than one-inch, squeeze concrete filler into the cracks and smooth and feather them out over the concrete with a trowel or putty knife. If the filler shrinks while drying, apply another coat until it is smooth.

For larger cracks, use a concrete patching compound, and pack it into the crevice as deeply as possible. For very deep cracks, lay the compound into the crack in successive layers to build it up gradually. For the last level, smooth and feather it as you would for smaller cracks.

Allow all crack repairs to dry for at least 24 hours before you walk on them to ensure that the repair materials will have adequate time to bond with the surrounding concrete and have lasting effect.

Tips and Warnings

  • For very large cracks, spray a layer of expanding foam into the crack before adding the first layer of compound, which will cause you to use less patching compound while keeping the same strength.
  • Allow the new concrete plenty of time to cure before walking on it.

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