How to Fix a Leaking Basement

Fix basement water leaks by identifying the source, sealing cracks with hydraulic cement or polyurethane sealant, improving drainage around your foundation, and applying waterproof coatings to walls.

1. Find Where Water Enters. Walk around your basement during and after heavy rain to pinpoint where water enters. Check for wet spots, stains, or active drips along walls, floors, and where the wall meets the floor. Mark these areas with chalk or tape. Also inspect outside your home for pooled water near the foundation, clogged gutters, or downspouts that dump water too close to your house.
2. Clear and Dry Surfaces. Remove any loose debris, old paint, or efflorescence (white chalky deposits) from crack areas using a wire brush or scraper. For active leaks, you may need to wait for a dry period or use a shop vacuum to remove standing water. Clean surfaces with a damp cloth and let them dry completely before applying any sealants.
3. Seal Cracks with Cement. For hairline cracks, apply polyurethane or silicone-based masonry sealant with a caulk gun, pressing firmly to fill the entire crack. For larger cracks up to half an inch wide, use hydraulic cement, which expands as it cures and stops active leaks. Mix the cement according to package directions and press it firmly into the crack with a putty knife, slightly overfilling then smoothing flush with the wall.
4. Inject Large Cracks. Cracks wider than half an inch or those that run horizontally may indicate structural problems. Clean out loose material and apply a concrete crack injection system, which uses low-pressure injection of polyurethane or epoxy. Follow the kit instructions carefully, drilling injection ports every 6-12 inches along the crack and sealing from the bottom up.
5. Redirect Water Away. Grade soil around your foundation so it slopes away from your house at least 6 inches over the first 10 feet. Clean gutters and extend downspouts to discharge water at least 4 feet from your foundation. Consider installing a French drain system if water consistently pools around your basement walls.
6. Coat Walls with Sealant. Once all cracks are sealed and cured, apply a waterproof masonry coating to basement walls using a brush or roller. Start with a primer designed for masonry surfaces, then apply two coats of waterproof paint, allowing each coat to dry completely. Pay extra attention to areas where walls meet the floor, as these joints are common leak points.
7. Add Sump Pump System. For persistent water problems, consider installing a basement drainage system with a sump pump. This involves cutting a channel around the basement perimeter, installing perforated drain tile, and connecting it to a sump pit. While this is a major project, it provides the most reliable long-term solution for chronic basement water issues.