How to Repair Tarmac Cracks – DIY Guide
How to Repair Tarmac Cracks
Fix tarmac cracks properly and stop water damage before it splits your driveway apart.
Repair tarmac cracks by cleaning out debris, applying a tarmac crack filler or cold-lay repair compound, tamping firm, and sealing the surface. Small cracks under 25mm wide are straightforward DIY. Work in dry weather above 5°C for the repair to bond correctly.
- Cold chisel
- Club hammer
- Wire brush
- Stiff broom
- Pointing trowel
- Tamping block or plate compactor
- Safety gloves
- Safety glasses
- Tarmac crack filler or cold-lay repair compound
- Tarmac sealant or bitumen emulsion sealer
- Kiln-dried sharp sand (for wide cracks)
- Weed killer or inhibitor
- Primer or bonding agent (for deep repairs)
- Grit or aggregate dressing
- Dust mask
Step-by-Step Guide
Clear and Prepare the Crack
Use a cold chisel and club hammer to chip away any loose or crumbling tarmac edges, then scrub the crack thoroughly with a wire brush to remove grit, moss, and debris. Any loose material left inside the crack will prevent the filler from bonding and the repair will fail within months. Treat any visible weed growth with a weed killer and allow it to die back fully before proceeding.
Clean and Dry the Area
Sweep out all loosened debris with a stiff broom and allow the crack to dry completely — damp tarmac will stop the repair compound from adhering. If the crack is deep (over 25mm), pack the base loosely with kiln-dried sharp sand to reduce the volume of filler needed and provide a stable substrate. Never attempt this repair in rain or when frost is forecast within 24 hours. For wider cracks across the whole driveway surface, see our guide to driveways and external surfaces for a broader assessment.
Apply Tarmac Crack Filler
Pour or trowel cold-lay tarmac repair compound into the crack in layers no deeper than 25mm at a time, slightly overfilling each layer before compacting. For hairline cracks under 5mm, a pourable bitumen-based crack filler applied direct from the bottle is sufficient. For cracks between 5mm and 25mm wide, use a cold-lay compound and press it firmly into the crack with a pointing trowel, ensuring no air pockets remain. If the surrounding tarmac surface is crumbling at the edges, address that before filling.
Compact the Repair Firmly
Tamp the filled compound down hard using a tamping block — a piece of timber off-cut works well for hand tamping — or a hired plate compactor for larger areas. The repair must be compacted in layers if the crack is deep; add compound, tamp, add more, tamp again. The finished surface should sit fractionally proud (1–2mm) of the surrounding tarmac to allow for final settlement under traffic. Proper compaction is the single most important factor in a lasting repair.
Seal the Repaired Surface
Once the filler has cured — typically 24–48 hours depending on temperature — apply a tarmac sealant or bitumen emulsion sealer over the repaired area using a brush or roller, feathering it out 100–150mm beyond the crack edges to blend it into the surrounding surface. Sealing locks out water and UV, which are the two main causes of tarmac deterioration. Scatter a light dressing of grit or fine aggregate over the wet sealant to improve grip and give a uniform finish. If you are planning to reseal the whole tarmac driveway, do the crack repairs first and seal everything together in one pass.
Allow Full Cure Before Use
Keep vehicles off the repaired area for at least 24 hours — longer in cold weather. Foot traffic can resume after a few hours once the surface is firm to the touch. Mark the area with cones or tape to prevent accidental damage during curing. Check the repair after the first heavy rain and tamp down any sections that have lifted slightly before resealing if needed.
Frequently Asked Questions
Can I repair tarmac cracks myself, or do I need a professional?
Cracks up to 25mm wide are straightforward DIY using cold-lay repair compound — no specialist equipment needed. Larger sections of failed or sunken tarmac, or cracks caused by a structural issue underneath, are better assessed by a surfacing contractor.
What is the best filler for tarmac cracks?
Cold-lay bitumen repair compound is the standard choice for cracks between 5mm and 25mm wide. For hairline cracks, a pourable bitumen crack filler applied direct is quicker and adequate. Avoid general-purpose sealants — they are not designed for flexible tarmac movement.
How long does a tarmac crack repair last?
A correctly prepared and compacted repair should last 3–5 years or more, particularly if the whole surface is sealed afterwards. Repairs that fail early are almost always caused by poor preparation or inadequate compaction rather than the filler itself.
Why does my tarmac keep cracking in the same place?
Recurring cracks in the same spot usually indicate a problem with the sub-base — either settlement, tree root movement, or poor drainage causing the ground to shift. Read our driveways guide for advice on diagnosing underlying causes before re-repairing the surface.
Do I need to seal tarmac after filling cracks?
Sealing is strongly recommended. Tarmac sealant protects the repaired area and the surrounding surface from water penetration, UV degradation, and oil contamination. It also blends the patch into the existing driveway for a neater finish. For a full walkthrough, see our guide to external surface repairs and maintenance.
Before filling, undercut the crack edges with a cold chisel to create a slight V-profile — this gives the filler a keyed, mechanical grip rather than a flat face bond, and dramatically improves how long the repair holds under repeated vehicle loading. Most DIY repairs fail at the edges, not the centre, so this one step makes the biggest difference.
Sources
- HSE — Working with bitumen and tar products: health and safety guidance — hse.gov.uk
- Which? — Driveway repairs: what to do and when to call a professional — which.co.uk
- GOV.UK — Planning permission: driveways and dropped kerbs — gov.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.
