How to Waterproof Basement Walls

Basements are naturally prone to dampness, but active water intrusion is a structural threat that needs immediate attention. You are essentially creating a barrier against the hydrostatic pressure pushing through your foundation, which requires patience and a methodical approach to ensure the seal holds over time. Done well, a waterproofed wall remains bone-dry to the touch even during heavy rain. If you rush the preparation or apply coatings over loose masonry, the seal will blister and peel within a year. Focus your energy on cleaning the substrate thoroughly, as the success of your waterproofing relies almost entirely on the bond between your sealant and the concrete.

  1. Expose Raw Concrete. Move everything away from the basement walls and remove any loose paint, wallpaper, or efflorescence using a stiff wire brush. If you see white, powdery mineral deposits, scrub them until the raw concrete is exposed.
  2. Seal Every Crack. Identify vertical cracks and the junction where the wall meets the floor. Use a chisel to widen these cracks into an inverted V-shape, then pack them tightly with hydraulic cement.
  3. Scrub the Foundation Clean. Wash the walls with a mild masonry cleaner or a stiff brush and water to remove oils and remaining dust. The concrete must be clean and slightly damp—but not dripping wet—before you apply any coatings.
  4. Force Paint Into Pores. Apply a high-quality masonry waterproofing paint using a thick-napped roller or a stiff masonry brush. Work the paint into the pores of the concrete rather than just rolling over the surface.
  5. Cross-Coat for Coverage. Wait for the first coat to dry completely according to the product manufacturer's instructions. Apply the second coat at a 90-degree angle to the first to ensure total coverage and structural integrity.
  6. Stop Water at the Source. Inspect your exterior gutters and downspout extensions to ensure they carry water at least six feet away from the foundation. Internal sealing is useless if you keep dumping roof water next to your walls.