A cracked concrete driveway is a common homeowner headache. Small cracks let moisture and freeze-thaw cycles worsen damage, create tripping hazards, and reduce curb appeal. Repairing cracks promptly slows deterioration and can avoid costly replacement later. This guide teaches DIY-friendly methods to assess crack type and size, choose the right materials, and complete repairs safely and durably. You will learn step-by-step preparation, filling techniques for different crack widths, finishing and curing tips, and when a professional replacement or structural evaluation is required.

Key Takeaways

Identify hairline vs structural cracks before choosing a repair method
Clean, widen, and undercut cracks to ensure a durable bond
Use backer rod and the correct filler (polyurethane or cement-based) for reliable results
Allow proper cure time and seal the surface to slow future damage
Call a pro for large, moving, or sinking cracks and exposed rebar

Tools Needed

Broom and leaf blower
Wire brush and stiff-bristle brush
Cold chisel and hammer or angle grinder with crack-chasing blade
Shop vacuum
Caulking gun (for sealants)
Trowel, putty knife, or margin float
Utility knife and measuring tape
Mixing bucket and drill mixer (for patch compounds)
Protective gloves, safety goggles, and dust mask

Materials Needed

Concrete crack filler (polyurethane or epoxy for active cracks)
Hydraulic cement or polymer-modified concrete patch for non-moving cracks
Backer rod (foam) for deep/wide cracks
Concrete bonding adhesive (primer)
Concrete sealer for the finished surface
Clean water and mild detergent
Sand (if mixing a patching compound)

⚠️ Safety Warnings

Wear eye protection, gloves, and a dust mask when cutting, grinding, or mixing products.
Avoid working on wet or icy surfaces. Do not use some sealants in temperatures below manufacturer recommendations.
Use caution with power tools; follow manufacturer instructions and keep bystanders away.
Some patching compounds and adhesives can release fumes; work in well-ventilated areas.

Step-by-Step Instructions

Step 1: Inspect and Assess Cracks

Walk the driveway and map all visible cracks. Measure width and length and note locations where the concrete is sinking, heaving, or where rebar shows. Hairline cracks under 1/8 inch usually need only sealing; cracks 1/8 to 1/2 inch can be filled with a concrete patch or caulk; cracks over 1/2 inch or with vertical displacement indicate potential structural or subgrade failure. Look for patterns like stair-step cracks along joints, which often point to foundation or soil movement and may not be a simple surface repair.

💡 Tip: Photograph cracks and label them to track whether they change after repair or over seasons.

⚠️ If you find exposed or corroded rebar, do not simply fill the crack—this can be a sign of serious deterioration.

Step 2: Clean and Prepare the Crack

Remove loose debris, dirt, weeds, and vegetation from the crack with a wire brush and broom. Use a shop vacuum to extract dust and small particles. For oil stains near repair areas, clean with a degreaser and rinse fully; repairs won't bond to oily surfaces. If the crack contains roots or packed soil, remove them to the depth of the crack. Ensure the surface is dry if using moisture-sensitive fillers—however, some products require dampened surfaces, so follow product directions closely.

💡 Tip: Blow the crack with an air compressor or leaf blower after brushing to get rid of fine dust.

⚠️ Do not ignore vegetation or roots in cracks; they will continue to grow and reopen the repair.

Step 3: Enlarge and Undercut the Crack

Create a uniform, stable profile for the repair by widening the crack slightly and undercutting the edges. Use a cold chisel and hammer or an angle grinder with a masonry blade to chase the crack to a V- or U-shape, about 1/4 to 1/2 inch wide at the surface. Undercutting the sides gives the patch a mechanical key to hold. For deep cracks, make sure there is room for backer rod and filler. Remove all dust and debris after chiseling with a vacuum and brush to ensure good adhesion.

💡 Tip: A V-shaped groove provides better bonding area than a thin slit and prevents the filler from popping out.

⚠️ Wear hearing protection and a dust mask when grinding or chiseling; flying fragments can cause injury.

Step 4: Install Backer Rod and Apply Bonding Agent

For cracks deeper than about 1/2 inch, push a compressible foam backer rod into the crack to leave space for the filler and control the filler depth. The backer rod should sit slightly below the surface. Apply a concrete bonding adhesive if using a cementitious patch; this improves adhesion to old concrete. For flexible sealants like polyurethane, most manufacturers recommend a clean, dry surface and no bonding agent. Always follow the specific product instructions for priming and recommended joint depth-to-width ratios.

💡 Tip: Choose a backer rod diameter slightly larger than the crack so it compresses snugly.

⚠️ Do not overfill deep cracks without backer rod—this wastes material and leads to weak repairs.

Step 5: Fill the Crack with Appropriate Repair Material

Select the correct filler based on crack type: use a polymer-modified patch or hydraulic cement for non-moving structural cracks; use a flexible polyurethane or silicone-based concrete crack sealant for active or hairline cracks. Mix cementitious products per instructions and pack them into the prepared groove with a trowel, slightly overfilling to allow for shrinkage. For caulking, apply the sealant with a caulking gun, forcing material deep into the crack and tooling smooth. Work in manageable sections and clean excess material before it skins over.

💡 Tip: For long cracks, work in sections to maintain control and finish uniformly.

⚠️ Mix patch compounds to recommended ratios; too much water reduces strength and increases shrinkage.

Step 6: Smooth, Cure, and Seal the Repair

Tool the repair flush with the surrounding surface using a trowel or putty knife and blend texture to match. Allow the material to cure per manufacturer recommendations—this can be 24 hours to several days. Keep traffic and vehicles off repaired areas until full cure. After curing, apply a concrete sealer across the driveway to reduce water penetration and slow future cracking. Reseal every few years as needed. Monitor repaired areas over the first year for signs of movement or re-cracking.

💡 Tip: Lightly mist cementitious patches during the initial cure if the product recommends moist curing to improve strength.

⚠️ Do not drive or park on freshly repaired sections until the product's full cure time has passed.

When to Call a Professional

Call a professional when cracks are wider than 1/2 inch, show vertical displacement, or when large sections of the driveway are sinking or heaving. These signs often indicate subgrade failure, inadequate base, or structural issues that a simple patch cannot fix. Professionals can evaluate drainage, soil conditions, and whether partial or full replacement is necessary. Also contact a pro if you see exposed or heavily corroded reinforcement (rebar), long stair-step cracks, or cracking that continues to grow after repairs. A contractor can provide a permanent solution, including base repair, slab jacking, or replacement, and will offer warranties and the equipment needed for larger jobs.

Frequently Asked Questions

How can I tell if a crack is structural or just a surface issue?

Structural cracks are typically wider than 1/2 inch, show displacement (one side higher than the other), form stair-step patterns near joints, or correspond with sinking/settling areas. Hairline or non-displaced cracks under 1/8 inch are often surface shrinkage. If in doubt, monitor the crack for change or have a professional inspect it to determine cause and recommended repair.

Can I use silicone caulk to fill driveway cracks?

Silicone is generally not recommended for concrete driveways because it doesn’t adhere well to dusty or porous concrete and can tear under vehicle loads. Use products formulated for concrete—polyurethane or specialized concrete crack sealants—for flexible, durable repairs, and use cementitious patches for non-moving cracks.

How long before I can drive over a repaired crack?

Cure times vary by product. Many flexible sealants set in 24 hours and reach serviceable strength in 48–72 hours. Cement-based patches can take several days to gain sufficient strength and up to 7 days for heavy loads. Always follow the manufacturer’s cure recommendations before allowing vehicle traffic.

Will a repaired crack reopen over time?

Repaired cracks can reopen if underlying issues like poor subgrade, drainage problems, or ongoing soil movement persist. Using the correct flexible filler for moving cracks and addressing drainage or base problems reduces the chance of recurrence. Monitor repairs and reseal as needed.

How To Repair Cracks Concrete Driveway