Concrete Driveway Cracks — When to Worry and When to Fix

You've spotted a crack in your concrete driveway. Your first thought: "Is this going to cost me thousands?" The good news is that not all concrete cracks are structural problems.

Here's how to tell the difference between a cosmetic crack and one that needs professional attention.

✅ Cosmetic Cracks (Don't Panic)

Hairline cracks (under 2mm wide) — These are almost always caused by normal shrinkage as the concrete cured. Almost every concrete slab has them. They don't affect the structural integrity and don't let water through. If they bother you cosmetically, fill them with a concrete crack filler or polyurethane caulk.

Crazing (spiderweb pattern) — Fine surface cracks that look like a cracked eggshell. Caused by rapid surface drying during cure. Purely cosmetic. No repair needed unless you're planning to seal the surface.

Cracks at control joints — That straight line in your driveway? It's a control joint, designed to encourage cracking in a straight line. If the crack follows the joint, it's working as intended. Leave it alone.

⚠️ Monitor These

Cracks 2–4mm wide — These might let water through and could widen over time. Fill with concrete crack filler and monitor annually. If they grow, escalate to professional.

One side slightly higher than the other (under 5mm) — Minor settlement. Watch it. If it stays stable for 12 months, it's not getting worse.

• Cracks wider than 4mm — structural cracks that let water through and may indicate slab failure
• Vertical displacement (one side 10mm+ higher) — trip hazard and sign of serious settlement
• Step cracks (going across the full width) — the slab may have completely separated
• Multiple parallel cracks — could indicate sub-base failure
• Cracks near a tree — tree roots may have grown under the slab and lifted it

Why Concrete Cracks

Concrete cracks because it's rigid. When the ground beneath it moves (clay soil swelling, tree roots, water erosion), the concrete has no give — so it cracks. Good installation minimises this with proper sub-base prep, reinforcement (steel mesh or fibre), and control joints spaced every 2.5–3 metres.

Can Cracked Concrete Be Resurfaced?

Yes — if the cracks are stable (not growing) and the slab hasn't shifted. A 15–20mm concrete overlay covers existing cracks and creates a fresh surface. We do this regularly across Sydney. It costs about $60–$90 per m² — much cheaper than replacement.

The bottom line: Fine cracks are normal. Widening or displaced cracks need attention. If in doubt, get a licenced concreter to look at it — most will inspect for free.