How to Repair Seepage in a Slab Foundation

Identifying the Source of Seepage

Start by locating where water enters the slab—common points are perimeter cracks, pipe penetrations, and low‑lying grading that directs runoff toward the foundation.

Preparing the Area

Clean the affected zone thoroughly; remove loose concrete, dirt, and any existing deteriorated sealant. Use a wire brush or pressure washer, then let the surface dry completely before proceeding.

Applying a Waterproofing Membrane

For most repairs, a liquid‑applied waterproofing membrane provides a seamless barrier. Roll or brush the product onto the cleaned slab, extending at least 6 inches beyond the crack or joint, and follow the manufacturer's cure time.

Sealing Cracks and Joints

Inject a polyurethane or epoxy crack filler into the opening, pushing the material deep enough to fill the void. After the filler cures, smooth the surface and re‑apply the waterproofing membrane over the repair.

Improving Exterior Drainage

Redirect surface water away from the foundation by grading the soil to slope at least 5% away, installing a French drain, or adding downspout extensions that discharge at least 6 feet from the slab.

Long‑Term Maintenance

Inspect the slab annually, especially after heavy rain, to catch new cracks early. Reapply sealant or membrane as needed, and keep the surrounding landscape well‑drained to prevent future seepage.

Comparison of Common Repair Methods