What causes driveways to crack?

expert EXPERT April 26, 2007

Cracking of asphalt or concrete surfaces may be caused by shrinkage, frost heave, settlement, or the effects of tree roots. If the sub-base was improperly prepared (base too thin or inadequately compacted) the surface is more prone to settlement or frost heave. In areas prone to frost, concrete and asphalt surfaces should have at least five inches of well compacted gravel below.

Concrete surfaces should have expansion and/or control joints. This prevents random cracking. A network of random cracks in concrete is an indication of a poor installation a poor concrete mix, a lack of control joints or an improper sub-base. Asphalt can develop fine cracks as it ages. Some recommend sealing asphalt every few years. Others discount the value of sealing. Heavy equipment or vehicles can cause surfaces to crack.

Damage can occur to asphalt or concrete if it is exposed to harsh chemicals, including automobile fluids or even ice-melting salts. Pavers (stone, clay, concrete) can spall in freezing weather if they are unsuitable for use in the ground. Clay brick pavers, for example, need to be very dense to resist water absorption. Mortar may also crack with frost, and will need periodic maintenance. Wood pavers will rot over time, even if they are pressure treated. Wood edging which holds pavers in place will also rot.

The important implication is a trip hazard. This is a safety issue. Cracks and damage can be cosmetic issues.

Checking paved surfaces for cracks or damage is easy. It's harder to notice conditions that may lead to damage in future. Look for missing edging, leaning support walls, wood beginning to rot, soil eroding beside the area, small trees which will grow quickly, pavers beginning to spall, or missing control joints.

Check for conditions that could lead to water accumulation, such as low spots, or downspout discharge. Strictly speaking, we don't predict future performance, but it's good to be aware of conditions which may affect performance.