Cracks in concrete driveways, sidewalks, patios, and garage floors are inevitable. Concrete expands, contracts, settles, and shifts over time. Ignoring cracks allows water to penetrate, freeze, and widen the damage. Timely repair is far cheaper than replacement. Here is how to fix concrete cracks and damage of various sizes.

How to Patch and Repair Cracked Concrete

Types of Concrete Damage

Hairline Cracks (Less Than 1/4 Inch)

Surface cracks from normal shrinkage. Cosmetic but can allow water penetration.

Structural Cracks (1/4 Inch and Wider)

Indicate settling, poor subgrade, or tree root damage. May require more extensive repair or professional evaluation if the slab is actively moving.

Spalling (Surface Flaking)

The top layer of concrete breaks away, exposing aggregate. Caused by freeze-thaw cycles, deicing salts, or poor finishing during original pour.

Broken or Heaved Sections

Individual sections of sidewalk or driveway that have lifted, sunk, or broken apart. Often caused by tree roots or poor drainage.

Repairing Hairline Cracks

1. Clean the crack with a wire brush and shop vacuum to remove all loose material and dust
2. Apply concrete crack filler (Quikrete or Sika brand, in a squeeze bottle or caulk tube) directly into the crack
3. Smooth the surface with a putty knife
4. Let it cure for 24 hours before foot traffic

For best adhesion, dampen the crack with water before applying the filler.

Repairing Cracks 1/4 to 1/2 Inch Wide

1. Use a cold chisel and hammer to undercut the crack edges slightly — making the crack wider at the bottom than at the top. This creates a mechanical lock that prevents the patch from popping out.
2. Clean all debris with a wire brush and vacuum
3. Apply a concrete bonding adhesive to the crack surfaces
4. Fill with vinyl-patching compound or hydraulic cement, pressing firmly into the crack with a trowel
5. Smooth the surface flush with the surrounding concrete
6. Cure for 24 to 48 hours, keeping it damp by misting with water

Repairing Large Cracks and Holes

For damage wider than 1/2 inch, deep holes, or broken edges:

1. Remove all loose and crumbling concrete with a cold chisel and hammer or an angle grinder with a diamond blade
2. Undercut the edges for a mechanical bond
3. Clean thoroughly with a wire brush and vacuum
4. Apply bonding adhesive to all surfaces
5. Mix concrete patching compound (for areas up to 1 inch deep) or standard concrete mix with added bonding agent (for deeper repairs)
6. Trowel the mix into the repair area, packing it firmly
7. Level and smooth with a finishing trowel, matching the texture of the surrounding concrete
8. Keep the repair damp for at least 48 hours during curing (cover with plastic or mist regularly)

Repairing Spalled Surfaces

Spalling requires resurfacing rather than filling individual spots:

1. Remove all loose, flaking material with a pressure washer or mechanical scraping
2. Clean the entire surface thoroughly
3. Apply a concrete resurfacer (Quikrete Concrete Resurfacer or similar) following the manufacturer’s instructions
4. Pour the resurfacer onto the dampened surface and spread with a long-handled squeegee
5. For texture, drag a broom across the surface before it sets
6. Keep damp during the 24-hour curing period

Concrete resurfacer can be applied as thin as 1/16 inch and restores a smooth, uniform surface over an entire slab. It is the most effective repair for widespread surface damage.

Sealing Concrete

After repairs cure, apply a concrete sealer to the entire surface. Sealers prevent water penetration, reduce freeze-thaw damage, and resist staining. Two main types:

• Penetrating sealers: Soak into the concrete and protect from within. Do not change the appearance. Last 5 to 10 years.
• Film-forming sealers: Create a glossy or matte coating on the surface. Provide more visible protection. Need reapplication every 1 to 3 years.

Apply sealer with a roller or pump sprayer on a clean, dry surface. Two thin coats provide better protection than one thick coat.

When to Call a Professional

• Cracks wider than 1 inch or actively growing
• Sections that have heaved or settled more than 1 inch
• Structural foundation cracks (call a structural engineer)
• Large-scale replacement of driveways or walkways
• Any repair that involves pouring new concrete slabs over existing

Prevention

• Seal concrete surfaces every 2 to 5 years
• Fill cracks promptly before water can enter and freeze
• Avoid using deicing salts on concrete less than one year old
• Maintain proper drainage away from concrete surfaces
• Trim tree roots that are pushing against or under concrete slabs

Concrete repair materials cost $5 to $40 depending on the scope of the repair. Addressing cracks and damage promptly prevents the need for expensive full replacement.