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The Best Way to Seal Basement Walls

By Adrian Grahams ; Updated September 21, 2017

Leaky basements can soon become damp and moldy. Water seeps through cracks in basement walls and moisture can penetrate tiny holes in porous masonry and concrete. An effective way to prevent damp and mold in basements is to patch all cracks with hydraulic cement and then seal the basement walls with a sealant that forms an impenetrable waterproof barrier.

Clean the basement walls by scrubbing them with a stiff brush dunked in hot water with a few squeezes of dishwashing detergent. Clean the walls thoroughly to remove all grime and dirt.

Rake the debris from all cracks in the basement wall with a wire brush. Wipe away dust with a cloth dampened with water.

Fill all cracks below 1/8-inch-wide with a regular waterproof interior filler. Use the supplied dispenser to push the filler into the cracks. Wipe off excess filler with a damp cloth.

Patch all cracks larger than1/8-inch-wide with hydraulic cement or an epoxy or latex-based waterproofing compound. Do this by pushing and spreading the cement or compound into the crack with a pointing trowel. Spread the cement so that it is flush with the wall surface. Again, wipe away excess cement, this time with the edge of the trowel blade and a damp cloth.

Wait for the filler and cement or compound to dry. Check manufacturer's instructions for drying times but this usually takes at least one week.

Pour the waterproof wall sealant into a bucket. Depending on the type of sealant, you may need to dilute the compound with water. Read the manufacturer's usage instructions for details. Mix the sealant thoroughly with a clean spatula or large spoon.

Paint on the waterproof wall sealant with a large paintbrush or a medium nap paint roller. Start from the top of the basement wall and work downwards. For rough textured masonry or brickwork, dab the sealant into rough and uneven areas with a stippling motion. Use protective gloves while using waterproof sealant.


Things You Will Need

  • Stiff brush
  • Dishwashing detergent
  • Wire brush
  • Interior filler
  • Cloths
  • Pointing trowel
  • Hydraulic cement or epoxy/latex waterproof compound
  • Waterproof sealant
  • Bucket
  • Paintbrush or paint roller
  • Protective gloves


  • Hydraulic cement is recommended for filling large cracks in basement walls. However, you can use an alternative. Make your own stiff mortar by mixing two parts fine sand with one part cement and a little water.


  • Always wear protective gloves while using waterproof sealants.

About the Author


Adrian Grahams began writing professionally in 1989 after training as a newspaper reporter. His work has been published online and in various newspapers, including "The Cornish Times" and "The Sunday Independent." Grahams specializes in technology and communications. He holds a Bachelor of Science, postgraduate diplomas in journalism and website design and is studying for an MBA.