How to Waterproof Stone Basements

Clean the interior walls of your stone basement. Use a wire brush to remove crumbling mortar and debris from the surface of the foundation walls. Pry out any loose or cracked mortar from between the stones.

Repair any obvious cracks with fresh mortar. Fill in loose joints between the stones with mortar, scraping off the excess with the edge of your trowel to form a smooth surface. Allow sufficient time for the mortar to set and dry completely. This may vary, depending on the temperature and the amount of humidity in your basement.

Caulk around any window wells and plumbing outlets, using a waterproof product. Press the caulking firmly into the narrow openings to seal off these avenues of moisture seepage. Let the caulking dry for the amount of time recommended on the product label.

Apply a substrate waterproofing primer to your walls, using a large paintbrush and a thick-nap roller. This product helps the waterproofing material adhere to your stone walls.

Apply a two-step waterproofing product to the interior of your prepared stone walls. Start with the liquid base coat, rolling and brushing it onto the primed surface of the stone walls of your basement. Let the base coat dry for the length of time recommended on the product label. Spread the topcoat over the dried base coat, using the brush and roller.

Repeat the two-step application process to spread on a second waterproofing base coat and topcoat. Very porous stone walls may require a third coat to ensure optimal leakage control.