How to Repair a Crack in a Concrete Wall

First decide whether DIY is appropriate

Many concrete cracks are cosmetic and can be sealed by a homeowner. Others indicate movement or pressure that a patch will not fix. Before buying materials, work out which type you have.

Consider a professional (a structural engineer or experienced foundation or concrete contractor) first if:

• The crack is in a foundation, basement, retaining or other load-bearing wall and is wider than about 1/4 inch.
• The crack is horizontal, or the wall bows or leans. See what a horizontal wall crack means.
• The crack is growing, or there are several cracks.
• One side of the crack is displaced (offset) from the other.
• Rust-coloured stains show along the crack, which can mean reinforcing steel is corroding.
• Water flows through the crack, or the crack is on a wall that holds back soil.

For these, patching alone can hide a problem without addressing it.

Why concrete walls crack

• Shrinkage while curing. Concrete loses water and shrinks, producing fine cracks that are very common.
• Temperature changes. Expansion and contraction can open cracks, especially in exterior walls.
• Settlement. Uneven soil support can crack a wall.
• Soil and water pressure. Wet or expansive soil can push on below-grade walls.
• Construction issues. Missing control joints, poor curing or insufficient reinforcement.
• Corrosion of reinforcing steel. Rust expands and can crack and spall the surrounding concrete. For how walls are reinforced in the first place, see foundation wall rebar spacing.

Choosing a repair material

The right product depends on the crack’s width, whether it moves, and whether it leaks. Always read the manufacturer’s instructions, since products differ.

• Hairline, non-moving cracks: a concrete or masonry crack filler or an elastomeric or acrylic masonry sealant is commonly used, mainly to keep water out.
• Narrow, stable structural cracks: epoxy injection is commonly used where the aim is to bond the concrete back together. It is generally for dry, non-moving cracks.
• Cracks that leak or may move slightly: polyurethane injection is commonly used because it stays more flexible and can seal against water.
• Wider cracks and surface defects: a cement-based repair mortar or patching compound may be used after cutting the crack out to a sound profile.
• Active water flow: hydraulic cement sets quickly and is often used to stop seepage while the source is addressed.

Can you use Quikrete to fill cracks in concrete? The brand makes several crack and concrete repair products, from sealants to repair mortars. Pick the product labelled for the type and width of crack you have, and follow its directions. A standard sand and cement mix is not usually the right choice for a thin crack.

How to repair a hairline or small crack

1. Wear eye protection, gloves, and a dust mask.
2. Clean out the crack with a wire brush, chisel and vacuum to remove loose concrete, dust and efflorescence.
3. If the product requires it, dampen the surface or prime it; others require a dry surface. Follow the label.
4. Apply the filler or sealant into the crack with a caulking gun or putty knife and smooth it flush.
5. Allow to cure as directed before painting or exposing to water.

How to repair a narrow crack with epoxy or polyurethane injection

Injection kits are sold for DIY use on vertical cracks. Typical steps:

1. Prepare the surface. Clean the crack and about an inch or two on each side, removing dirt, paint and loose material.
2. Fit injection ports. Ports are spaced along the crack, often at intervals roughly matching the wall thickness or as the kit specifies.
3. Seal the surface. Cover the crack between ports with the kit’s surface sealer or paste so the injected material does not leak out. Let it cure.
4. Inject. Start at the lowest port on a vertical crack and work upward, injecting until material appears at the next port, then cap that port and move on.
5. Cure and finish. After the specified cure time, remove the ports and grind or scrape the surface seal flush.

Temperature, moisture and mixing ratios matter, and the instructions vary by product, so read them closely. Kits are best for limited, stable cracks; a leaking basement wall crack that keeps coming back justifies a professional opinion.

Common mistakes

• Patching a moving crack. If the crack widens again, the cause has not been fixed.
• Skipping preparation. Dust, loose concrete and laitance prevent adhesion.
• Using the wrong product. Rigid epoxy in a crack that moves, or a thin sealant in a wide structural crack.
• Sealing the inside only. If water pressure comes from outside, the underlying drainage issue still needs attention; see water leaking through a foundation or basement.
• Ignoring rust stains or displacement.
• Not measuring first. Date and measure the crack, and watch it over time to see if it is active. A crack width gauge is inexpensive.

When to call a professional

Call for help with structural walls, widening cracks, leaks, rust staining or bowing, or if you are uncertain about the cause. For outdoor walls that hold soil, see cracks in a retaining wall. For general triage of cracks inside the house, see interior wall cracks: when to worry.

FAQ

What are the common mistakes to avoid when repairing concrete cracks?

Poor cleaning, using the wrong material for the crack type, patching a crack that is still moving, and ignoring the water or soil problem behind it.

What is the best material to fill cracks in walls?

It depends. Sealants for hairline cracks, epoxy for stable structural cracks, polyurethane for leaking or slightly moving cracks, and cement-based mortar for wider surface repairs.

Can I use Quikrete to fill cracks in concrete?

Use the specific Quikrete crack or repair product designed for your crack type, and follow the label.

How can I repair my foundation?

Foundation repair depends on the cause. Minor shrinkage cracks may be sealed, but movement, bowing or wide cracks need a structural engineer’s assessment. For leaking foundation cracks specifically, see foundation crack leaking water.