How Can I Seal a Damp Concrete Floor?


Damp concrete floors are often common in garages. Chances are that when the concrete was poured, no plastic was laid beneath it to form a vapor barrier. Basements with this problem may have to use a dehumidifier to remove excess moisture from the area. Lack of air circulation or a bad seal between the walls and floor can be a cause for damp floors in basements. The source of moisture should be found before the sealer is applied to the floor.

Check for Leaks

  • Make an inspection of all water and drain pipes. If water is concentrated in one area, there may be a leak above. Inspect all walls to floor joints as well as any expansion joints in the slab itself. These areas should be sealed with a high-quality silicone caulking. Check with the manufacturer of the floor sealer you are going to use so the caulk does not react poorly with the sealer. The caulk should be thoroughly cured before applying any sealer.

Get it Dry

  • The concrete floor will have to be dry before applying the sealer. This may entail the use of a dehumidifier for basement areas. A large fan can be used in a garage area to keep the air moving over the slab. Keep an eye on the environment or weather. Rainy days or high humidity may not be the best day to apply any type of coating, even if the concrete appears to be dry. Excess moisture may impede the curing of the sealer.


  • If there are signs of mold growth near the base of walls and the floor, you may need to apply a fungicide before the application of the sealer. This could entail scrubbing the corners of the slab area with a stiff bristle brush and then rinsing clean. Allow the area to dry completely. Most sealers may have to be applied in one sitting to form a good mechanical seal over the concrete. This may include sealing the corners first with a brush and then covering the entire floor area with a roller application. Follow the manufacturers specifications for the particular products. In cases where basements did not have a plastic vapor barrier installed below the slab, a dehumidifier may have to be run in high-humidity weather even after a sealer was installed.

Raise the Floor

  • A framed floor can be added above the concrete slab as a last resort. In this case, a plastic sheet vapor barrier will have to be laid between the slab and the rot-resistant wood. Green, treated wood may be the best choice for framing lumber. To prevent future mold growth, you may still need to use a dehumidifier.


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