How Waterproof Interior Basement Walls

Keeping your basement dry can be especially challenging, particularly with heavy rainfall or with the arrival of spring. Applying a waterproof sealant to the inside of the basement walls can alleviate many problems related to moisture. Applying this sealant is as simple as using a paint roller, however, it takes a lot of work to prepare the walls for sealing. With the right tools, you can waterproof your basement walls in a weekend.


  1. Remove all loose paint, concrete, dust and other similar elements from the walls with a metal bristle brush. Brush in deep areas surrounding any breakage to prepare for hydraulic cement.
  2. Clean the walls with a concrete degreaser cleaner. Follow the manufacturer’s instructions for mixing the cleaner. Apply with a sprayer to accelerate the process. Brush the walls with the swab to remove fat deposits and other impurities. Rinse the wall and let it dry as directed by the cleaner.
  3. With a chisel, remove chunks of concrete that are broken or loosen holes that are in the walls. Use chisel to trim the edges to allow the hydraulic cement to adhere to the walls.
  4. Following the instructions, mix small amounts of hydraulic cement. Place the cement in the cracks and holes and be sure to seal completely. Smooth the surface of the concrete with a trowel until it is flush with the surface of the walls. Let the cement dry as instructed.
  5. Apply a paint primer with a thick bristled roller, if necessary, making sure you get to the corners of the walls and the area around the repair. Let it dry and if needed apply a second coat.
  6. Waterproof inner walls by applying the sealant with a roller. Make sure the repaired areas are properly sealed. The same should happen with the edges and corners. Let the sealer dry according to instructions. Apply a second coat if necessary.

Tips & Warnings

  • Before waterproofing the inside walls of your basement, make sure that humidity is an external problem. Tape a piece of plastic with a damp spot on the wall. The next day inspect it to see if moisture is on the side facing the wall, indicating a problem of external moisture, or the area exposed to air, indicating a problem of interior moisture.
  • Use protective goggles when brushing, cleaning and using the chisel on the wall for protection. Make sure the area is well ventilated before applying the sealant.