How to Repair a Crack in a Concrete Foundation

Assess the Crack Before You Repair It

Small, vertical cracks in a concrete foundation are common and often cosmetic, but horizontal or stair-step cracks can signal serious structural movement. Before buying any product, clean the crack thoroughly with a wire brush and compressed air, then determine whether it is active or stable by marking its ends and monitoring it over several weeks.

For cracks narrower than 1/8 inch, a concrete crack filler or flexible sealant is usually sufficient. Wider cracks or those showing water penetration require an epoxy or polyurethane injection system that locks the fracture from within.

Materials and Tools You Will Need

• Wire brush and vacuum
• Concrete crack filler or hydraulic cement
• Epoxy or polyurethane injection kit
• Putty knife or caulking gun
• Safety glasses and gloves

Step-by-Step Repair Process

Step 1: Prepare the Surface

Remove loose debris and dampness from the crack. If the concrete is crumbling, chisel out weak edges to create a clean, stable profile for the filler to bond.

Step 2: Choose the Right Filler

For minor cracks, apply a ready-to-use concrete crack filler with a putty knife, pressing it firmly into the opening. For deeper or wider cracks, mix hydraulic cement or use an injection resin that expands as it cures to fill the void completely.

Step 3: Seal and Protect

Once the filler has cured, apply a waterproof sealant over the repair and the surrounding area. This prevents moisture from re-entering the crack and causing further freeze-thaw damage.

When to Call a Professional

If the crack is wider than 1/4 inch, shows horizontal displacement, or is accompanied by bowing walls, floor settlement, or persistent water leaks, consult a structural engineer. These signs can indicate foundation settling, soil pressure, or hydrostatic issues that a simple surface repair will not resolve.