Cracked concrete driveway: repair, resurface or replace? (Lower Mainland)

How big of a crack is acceptable in concrete?

Hairline cracks, about the thickness of a bank card or less, are common in concrete and usually come from shrinkage as the slab dried. If both sides of the crack sit level and the crack isn't growing, it's cosmetic.

A rough rule of thumb is to pay attention once a crack is wider than about 6 mm (1/4 in.), or when one side sits higher than the other. Put a coin against it and check again in a few months. A crack that keeps opening is telling you the ground is moving.

What types of cracks can you not ignore?

A sunken section, where a level laid across the slab shows a dip, means the base has washed out or compressed. A heaved joint, where one panel has lifted, is often tree roots or frost. Roots lifting an edge will keep lifting it.

Water is the other warning sign. If water sits against the garage or runs under the slab, the ground beneath is softening. Cracks that let water in during winter get wider each freeze. Any of these means the problem is under the concrete.

Can you pour concrete over concrete to fix cracks?

Sometimes. A resurfacing overlay works on a slab that's sound and level with a worn or scaled surface. The old surface is cleaned and prepared, and a thin bonded layer goes on top.

It doesn't work on cracks that are still moving or a slab that's settling. The cracks come straight back through the new layer. An overlay also raises the surface, which can cause trouble at the garage door and the street edge.

Repair, resurface or replace: which one does yours need?

Repair means cleaning and sealing cracks, and it suits hairline and small stable cracks. Resurfacing suits a sound slab with a tired surface. Replacement is for a driveway with a failed base, wide moving cracks, or panels that have sunk or broken up.

If only one or two panels have failed, those panels can sometimes be cut out and replaced on their own. The new concrete won't match the old in colour, which bothers some people more than others.

The estimate visit: measuring, crack map, then the estimate

The visit starts like any driveway estimate. Length, width, the slope from the garage to the street, the apron and the garage edge. Each crack gets mapped and photographed so the estimate matches what's there.

A replacement estimate adds lines a new driveway doesn't have. Saw-cutting at the garage and the apron, breaking out the old slab, hauling it away and disposal.

What replacement involves: the old slab out, then a new driveway

The old driveway is saw-cut where it meets the garage and the apron, so the edges stay clean. It's broken out and hauled away, commonly to a concrete recycler. Then the base underneath gets checked, because whatever made the old slab fail has to be fixed first. A poor base, roots or bad drainage will crack the new slab the same way.

From there it's built like a new driveway, with base, forms, steel, the pour and control joints. If the replacement is wider at the street, Maple Ridge needs an application to Engineering, accepted before work starts.

Send a photo of the cracks with the booking form, with a coin beside the widest one. John will tell you whether it's a repair or a replacement.

Source: Maple Ridge Driveway Crossing, Culvert and Ditch Infill application

The bottom line

Hairline cracks are normal and can be sealed, and a sound slab with a worn surface can be resurfaced. A driveway that has sunk, heaved or broken into pieces has a failed base, and replacing it is the only fix that lasts.