Why Your Concrete Driveway Is Cracking: Which Cracks Matter and What to Do

Why is my concrete driveway cracking? Usually because concrete shrinks as it cures, and thin, level cracks along joints or across the slab are normal. Wide, growing or uneven cracks, or a slab that has sunk or heaved, point to a base, drainage or freeze-thaw problem. Flaking, pitting and crumbling are a different failure, caused mostly by salt and freezing at the surface.

Why is my concrete driveway cracking? Read the crack first

The pattern tells you more than the crack itself. Look at width, direction, whether both sides sit level, and whether it has changed since last year.

Do concrete driveways always crack?

Almost every slab shows some cracking over time. Concrete shrinks as it dries and as temperatures drop, but the base and edges hold it in place, so it cracks. Control joints are grooves cut or tooled into the surface so that the cracking happens along straight, planned lines rather than across the middle of a panel.

A crack that follows a joint is the design doing its job. A crack that wanders usually means the joints were too far apart, cut too late or too shallow. Cracking by itself is not a failure. Judge it by three things: whether it is wide, whether the two sides are level, and whether it is growing. A hairline you can barely feel with a fingernail is cosmetic. A crack that catches a fingernail, or a step between the two sides, deserves attention.

What causes serious cracking under Ontario conditions

When cracks are wide or uneven, the cause is usually underneath or around the slab.

• Weak base. A driveway needs a compacted granular base. Soft spots, poorly compacted fill or an old utility trench can let a section settle.
• Water. Roof water discharging onto the driveway, ground that slopes toward the slab, or a clay soil that stays wet all feed the base. Water that freezes under the slab can lift it, and it drops again when it thaws. Frost reaches about 1.2 m (4 feet) deep in this region.
• Heavy loads. A slab that is too thin, or has no reinforcing steel or mesh, can crack under delivery trucks, a bin or an RV.
• Tree roots. Roots lift edges and corners near large trees.
• Placement and curing. Added water in the mix, fast drying on a hot or windy day, or poor curing weaken the surface and raise the chance of random cracks.

Several of these work together. Water in a weak base is the usual combination behind a driveway that sinks in the middle or at one corner. Our post on downspout management explains how to send roof water somewhere harmless.

Why is my concrete driveway crumbling, flaking or pitting?

These are surface failures, and cracks are not the main issue.

• Flaking (scaling). A thin skin peels away and exposes the stone beneath. Salty meltwater soaks in, freezes, and pushes the surface off. It is most common on concrete that lacks enough air entrainment, was overworked during finishing, or met de-icing salt in its first winter.
• Pitting. Small holes or cone-shaped popouts appear where a soft particle or a bit of stone near the surface froze and broke loose. Scaling often follows pitting.
• Crumbling edges and corners (spalling). Edges take the most water and salt, so chunks break away there first, especially where concrete was weak to begin with.

Exterior concrete that faces freezing and de-icing salt should be air-entrained, and 32 MPa is a common strength for this exposure. Avoid de-icing salt on new concrete through its first winter. On older concrete, use less. The Smart About Salt Council says about one tablespoon of salt per square metre of slab is often enough, applied thinly, and that salt works best between 0 and -10 C. Sand gives traction when it is colder.

Can you repair a concrete driveway? Patch, resurface or replace

The right repair depends on what is wrong and whether the slab is still sound.

• Patch or seal. Choose this for level cracks that are not growing and small chips. Sealing keeps water out of the crack and the base.
• Resurface. Choose this when the slab is flat and solid but the surface is scaled, pitted or worn. A contractor applies a thin bonded overlay. It fails if the slab below is moving, and it fails again if salt use does not change.
• Replace. Choose this when sections have sunk or heaved, cracks are wide and spreading, large areas are crumbling, a slab rocks underfoot, or water runs toward the house. Cracked or heaved slabs are often removed and re-poured, and the cause (base, drainage or salt) is addressed so the new slab does not repeat the failure.

Replacing a single bad panel can work where the joints allow it. The new concrete may not match the colour and weathering of the old, so ask what to expect. For a view of when cement work is due, see signs you need cement work in Waterloo Region.

How to patch a concrete driveway crack

A small, stable crack is a reasonable DIY job. Follow the product maker's instructions, since temperature limits and cure times vary.

1. Choose a dry day above the product's minimum temperature. Spring after the thaw and early fall work well.
2. Clean out the crack with a wire brush, then remove dust and loose bits. Let it dry.
3. Use a flexible concrete crack filler or sealant for cracks that open and close with the seasons. A rigid patch alone tends to pop out.
4. Fill from the bottom up, level it with the surface and smooth it.
5. Keep traffic and water off until the product has cured.

For chips and shallow spalls, use a concrete patching product made for exterior use and follow its surface preparation steps. Do not patch over a crack with a step in it. That is a base issue, and a patch will not hold.

Prevent more damage, and when to call a pro

Move roof water away from the slab with downspout extensions, and keep the ground sloping away from the driveway edges. The Government of Canada suggests extending downspouts at least 2 m (6 ft.) away from the foundation where possible, and the same logic keeps water off concrete. Use salt sparingly, keep trees from crowding the edges, and seal cracks before winter.

Call a concrete contractor when slabs are settling, heaving or crumbling, or when you are not sure what is under the surface. D&D Exterior Finishing builds concrete driveways with a compacted granular base, reinforcing steel or mesh, control joints and proper curing, and the free written estimate explains how the cause of the failure will be addressed. See the concrete driveway and repair service, or read how to choose a concrete contractor before you compare quotes.

Concrete driveway cracking questions

Do concrete driveways always crack?

Almost always, to some degree. Concrete shrinks as it cures and as temperatures change, so most slabs develop cracks. Control joints guide them into straight lines. Level, hairline cracks are normal. Wide cracks, steps between sides or growing cracks point to base, drainage or freeze-thaw problems.

Why is my concrete driveway crumbling?

Crumbling is usually surface damage from freezing and de-icing salt, often at edges and corners where water collects. Concrete that lacks enough air entrainment, was finished poorly or met salt in its first winter is more likely to fail. Reduce salt use and talk to a contractor about resurfacing or replacement.

Can you repair a concrete driveway instead of replacing it?

Yes, when the slab is level and sound. Stable cracks can be sealed, chips patched, and a scaled surface resurfaced. Sunken, heaved or widely cracked sections usually need to be removed and re-poured, with the base and drainage fixed so the problem does not return.

How do you patch a crack in a concrete driveway?

Clean the crack with a wire brush, remove dust, let it dry, and fill it with a flexible concrete crack sealant on a dry day above the product's minimum temperature. Smooth it level and keep traffic off until it cures. Follow the manufacturer's directions, and do not patch a crack that has a step.

Is a cracked concrete driveway a structural problem?

Not usually. Many cracks are cosmetic shrinkage. It becomes a concern when the crack is wide and growing, the two sides are uneven, or the slab has sunk. Those signs point to a weak or wet base and are worth having a contractor assess before winter.

Devon Moore, Operations Lead Co-Founder & Operations Lead — D&D Exterior Finishing

Devon Moore is the co-founder and Operations Lead at D&D Exterior Finishing, specializing in siding, roofing, windows, and exterior renovations across Waterloo Region.