Concrete Crack Repair

First: repair, or replace?

• Repair: cracks up to about 1/2" wide where both sides are level
• Level then repair: one side is raised or sunk (a trip hazard). Grinding or slab lifting may fix it.
• Replace: the slab is broken into many pieces, crumbling, or heaved badly

Choosing the right concrete crack filler

Filler	Best for
Self-leveling polyurethane sealant	Horizontal cracks up to ~1/2" in driveways, patios and garage floors. Flexible.
Polyurethane caulk (non-sag)	Vertical surfaces and sloped areas
Epoxy crack filler or injection	Rigid structural bonding of dry, stable cracks
Vinyl or latex concrete patch	Wider, shallow cracks and spalled areas. Trowel-applied.
Concrete repair mortar	Large cracks, broken edges and deep repairs

More detail is in our concrete crack filler guide.

How to fix small cracks in concrete (under 1/4")

1. Clean out debris with a wire brush or screwdriver, then vacuum or blow out the dust.
2. Let the crack dry completely, unless your product is rated for damp concrete.
3. Apply a self-leveling sealant (flat surfaces) or polyurethane caulk (vertical surfaces), slightly overfilling.
4. Smooth with a putty knife, and keep traffic off until fully cured. Check the label, often 24–48 hours.

How to fill large cracks in concrete (1/4" to 1/2" and up)

1. Chisel the crack into an inverted V (wider at the bottom), so the patch locks in.
2. Remove loose material and dust, and dampen the concrete if your patch product requires it.
3. For deep cracks, push in a foam backer rod so the sealant is no deeper than about 1/2". This saves material and helps the sealant flex.
4. Fill with a concrete patch or repair mortar for rigid repairs, or a polyurethane sealant for joints that move.
5. Trowel flush, texture to match (a broom finish outdoors), and cure as directed.

Garage floor and pool deck cracks

For garage floors, fill cracks before applying any epoxy coating, using an epoxy crack filler that bonds with the coating. For pool decks, use flexible polyurethane sealants rated for UV and water, since decks expand and contract a lot in the sun.

Prevent cracks from coming back

• Keep water away: fix downspouts and drainage that pond water on or beside slabs
• Seal concrete every few years with a penetrating sealer
• In cold climates, avoid de-icing salts on concrete less than a year old
• Keep control joints clean and sealed. They exist so the concrete cracks there instead of randomly.