How to Repair Cracks in a Concrete Floor

Concrete floors in garages and basements inevitably crack as the building settles and the material shrinks over time. While most hairline fractures are purely cosmetic, larger cracks can allow moisture to seep through, potentially damaging your flooring or creating a home for pests. Fixing these cracks requires more than just pouring filler into the gap; you need to create a clean, keyed surface that the patch material can actually grip. Done well, the repair will be flush with the floor, preventing further erosion and keeping your slab surface smooth and durable for years to come.

1. Clear Away Loose Debris. Use a stiff wire brush to scrub the inside of the crack, removing loose grit, dust, and old debris. Vacuum the area thoroughly to ensure the surface is completely clear so the filler can bond to solid concrete.
2. Shape the V-Channel. Use a hammer and a masonry chisel to chip away at the edges of the crack to create an inverted V-shape. Ensure the crack is at least 1/4 inch deep and wide throughout its length to give the filler enough mass to hold.
3. Eliminate Dust Completely. Vacuum the V-shaped channel one last time to remove any concrete dust generated during the chiseling process. Wipe the area with a damp cloth if needed, then let it dry completely before proceeding.
4. Lay Your Foundation Base. If the crack is deeper than 1/2 inch, press a foam backer rod into the gap to act as a base. This prevents the filler from sinking too deep and ensures the material stays near the surface.
5. Fill the Gap Flush. Load your polyurethane concrete filler into a caulking gun and dispense it steadily into the crack. Start at one end and pull the gun toward you, filling the gap slightly above the level of the surrounding floor.
6. Strike It Smooth and Flush. Use a metal putty knife to strike off the excess filler, pressing it firmly into the crack to eliminate air pockets. Level the material so it sits perfectly flush with the surrounding concrete.