How to Repair a Cracked Driveway – DIY Guide
Driveways & External › Concrete
How to Repair a Cracked Driveway
Fill and seal driveway cracks yourself and stop them spreading for good.
Repair a cracked driveway by cleaning out the crack, undercutting the edges, applying a suitable filler compound, and sealing the surface once cured. Most hairline and structural cracks in concrete or tarmac can be fixed in a single afternoon with basic tools.
- Cold chisel
- Club hammer
- Wire brush
- Angle grinder with diamond blade
- Pointing trowel
- Stiff-bristle brush
- Pressure washer or hosepipe
- Safety glasses
- Concrete crack filler or repair mortar
- Polyurethane joint sealant
- Bonding agent or PVA adhesive
- Sharp sand
- Cement
- Weed killer or moss and algae treatment
- Masking tape
- Driveway sealant (optional, for concrete)
Step-by-Step Guide
Clear and Clean the Crack
Remove all loose material, weeds, and debris from the crack using a cold chisel, wire brush, and stiff-bristle brush. Kill any weeds at the root with a suitable weed killer and allow it to work before proceeding — leaving organic matter inside the crack will cause the repair to fail within months. Rinse the area thoroughly with a pressure washer or hosepipe and allow it to dry completely.
Undercut the Edges for a Mechanical Key
For cracks wider than 5 mm, use a cold chisel and club hammer — or an angle grinder with a diamond blade — to slightly widen and undercut the crack edges into a dovetail profile. This creates a mechanical key so the filler locks in rather than sitting on top of the surface. Brush out all dust and debris once complete. For hairline cracks under 3 mm, skip this step and move directly to priming. If you are also dealing with repointing patio slabs, the same undercutting principle applies to failed mortar joints.
Prime the Crack with Bonding Agent
Brush a coat of bonding agent or diluted PVA adhesive into the crack and onto the surrounding 50 mm of surface. This prevents the dry concrete or tarmac from drawing moisture out of your repair mix too quickly, which causes shrinkage and cracking. Allow the primer to become tacky — typically 10–20 minutes — before applying filler.
Fill the Crack in Layers
For deep cracks over 20 mm, build up the repair in layers no more than 20 mm deep at a time, allowing each layer to firm up before adding the next. Use a ready-mixed concrete repair mortar or a sand-and-cement mix at a 3:1 ratio for structural cracks; use a flexible polyurethane joint sealant for cracks in expansion joints or between surfaces. Press the filler firmly into the crack with a pointing trowel, ensuring no voids or air pockets remain. Our Driveways & External Guide covers material selection for different driveway types in more detail.
Finish and Feather the Surface
Once the crack is filled flush, use a damp trowel to smooth and feather the repair into the surrounding surface so it sits level. Avoid over-trowelling, which brings cement laitance to the surface and weakens the repair. Apply masking tape either side of the crack before filling if you want a clean, defined edge — particularly useful on tarmac where the filler colour contrasts with the surrounding surface. For larger areas of surface damage, consider whether laying a new patio or surface is a more cost-effective long-term solution.
Cure and Seal the Repair
Keep the repair damp for at least 24 hours by covering it with damp hessian or polythene sheeting — this slows the curing process and produces a stronger, more durable result. Do not allow vehicles onto the repair for a minimum of 48 hours, and ideally 72 hours in cold weather. Once fully cured, apply a concrete driveway sealant over the entire surface to unify the appearance and protect against water ingress, freeze-thaw damage, and oil staining. Regular sealing is one of the most effective ways to prevent cracks returning — the pressure washing your driveway guide explains how to prep the surface before sealing.
Frequently Asked Questions
What is the best filler for a cracked concrete driveway?
For structural cracks, a ready-mixed concrete repair mortar gives the best results — it is pre-blended for strength and workability. For narrow hairline cracks and expansion joints, a flexible polyurethane sealant is more appropriate as it accommodates surface movement without re-cracking.
Can I repair a cracked driveway in cold weather?
Avoid repairs when temperatures are at or below 5°C — cement-based fillers will not cure properly and may freeze before hardening. If you must work in cooler conditions, use a rapid-set repair mortar and cover the finished repair with frost protection sheeting for at least 24 hours.
How do I stop cracks coming back after repair?
Address the root cause first — cracks are commonly caused by tree root pressure, inadequate sub-base depth, or water erosion beneath the surface. Sealing the driveway after repair and managing drainage around it will significantly reduce the chance of new cracks forming. You can also remove oil stains from your driveway before sealing for the best finish.
How wide does a crack need to be before I should call a professional?
Cracks wider than 25 mm, cracks accompanied by significant vertical displacement between the two sides, or cracks spreading rapidly across a large area can indicate a failing sub-base and may require professional reinstatement. For cracks under 25 mm with no vertical movement, DIY repair is entirely suitable.
Does repairing a cracked driveway require planning permission?
Repairing an existing driveway surface does not require planning permission. However, if you are replacing or extending a front driveway with an impermeable surface over 5 m², you may need permission or to use a permeable surface — check the current rules on the GOV.UK planning portal.
When mixing a sand-and-cement repair mortar for a crack, add a small measure of bonding agent to the gauging water rather than plain water — this significantly improves adhesion and reduces shrinkage without altering the workability of the mix.
Sources
- HSE — Working safely with cement and concrete products — hse.gov.uk
- GOV.UK — Do I need planning permission for a new driveway? — gov.uk
- Which? — How to repair a driveway — which.co.uk
This guide is for general information only. Always work safely and follow manufacturer instructions. DIYnut accepts no liability for injury or damage arising from DIY work.
