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Causes of Basement Floor Cracks and What to Do About Them

Wednesday, August 28th by Kristina McGovern


Close-up of a crack in a concrete basement floor

Cracks in the basement floor can let in water, moisture, and radon gas.

Learn why basement floors crack and whether the cracks in your basement floor are normal or need to be fixed.

Cracks in the basement floor can be a cause of panic for homeowners. The good news is most basement floor cracks are normal and don’t need to be repaired. The basement floor doesn’t support the weight of the home, so cracks in the floor won’t affect the home’s structural integrity. However, some cracks in the basement floor can let water, moisture, and dangerous soil gasses into your home.

If you have a crack in your basement floor, determine the type of crack and what’s caused it to figure out how to best solve your problem.

Why do basement floors crack?

It’s very common for cracks to form in a home’s foundation after it’s built. Most times the cracks are normal, non-structural settlement cracks. However, there are many reasons why a foundation cracks, such as settling of the home, concrete shrinkage and curing, stress, and poor construction.

6 types of basement floor cracks - and what they mean

  1. Cracks with heaving are signs of a bigger problem that needs to be addressed. When a basement floor crack is combined with heaving, this is a cause for concern. Heaving suggests that the soil beneath the basement floor is expanding. Heaving is especially common in areas with clay soil. When the soil becomes wet, it creates enough pressure to lift and crack a concrete slab floor.

    What to Do: Call a professional foundation repair contractor. They can assess the situation and recommend the best solution.

  2. Concrete floors with cracks ½ or larger should be leveled. When a foundation settles, the concrete slab can crack and the part of the slab that's less supported sinks into the depression. The resulting uneven surface can create a tripping hazard.

    What to Do: Concrete basement floors that are uneven should be leveled. PolyLevel uses a high-density polyurethane formula to permanently lift and stabilize a sinking concrete slab. Penny-sized holes are drilled into the slab and a structural-grade polymer is injected into the void. The polyurethane material expands, lifting and leveling the slab.

  3. Wall-floor joint cracks should be sealed. When the concrete floor pulls away from the basement walls, this can result in cracks along the perimeter of the basement, where the floor meets the walls.

    What to Do: Cracks along the wall-floor joint should be sealed to keep out water and moisture.

  4. A finished basement with faux-wood plank flooring

    Basement remodeled with ThermalDry Elite Plank flooring.

    Hairline cracks don’t require repair. Small cracks in the basement floor commonly result from shrinkage as the concrete dries, which pulls the concrete apart. These types of cracks can show up as long as a year after the basement floor is poured, depending on how quickly the slab dries and how humid the basement is.

    What to Do: Nothing. Hairline cracks in the basement floor are superficial and don’t require repair. If you are worried about how they look, you can cover the concrete with basement-friendly flooring like Basement Systems’ ThermalDry wood-look plank flooring or carpeted flooring.

  5. 1/8-inch or wider cracks should be sealed. Like hairline cracks, these cracks that are slightly wider are likely the result of shrinkage and are not a sign of a serious foundation problem.

    What to Do: Cracks wider than ⅛-inch should be sealed to help keep water, moisture, soil smells, and radon gas from seeping through the basement floor.

  6. Spalling or flaking is ugly but doesn’t require repair.  It can occur when the concrete mix is too wet or hasn’t been properly cured. The water evaporates and loosens the top layer of the concrete, causing it to flake off. Concrete spalling is unattractive, but chances are the slab is still in good shape.

    What to Do: Don’t try to hide the problem with paint. The surface of the floor is likely to keep flaking and when it does, it will take the paint off too. Consider concrete resurfacing to make the concrete look like new and prevent future spalling. Another option is to install waterproof flooring over the concrete.

How's your drainage?

If the soil around the foundation is poorly graded or you have improper drainage, water can build-up and put pressure on the foundation, causing it to crack. There are simple steps you can take to relieve hydrostatic pressure and help prevent cracks in your basement.

What to Do:

  • Make sure landscaping is properly graded and slopes away from the foundation.
  • Keep your gutters clean and in good working condition. Install gutters and downspouts if you don’t have them.
  • Extend your downspouts away from the house to keep them from dumping water close to the foundation walls.
  • Add interior perimeter drainage and a good sump pump system in the basement.

If you'd like a professional evaluation of your basement floor cracks or you are dealing with water intrusion in the basement, contact us for a free basement crack repair estimate!

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