My concrete driveway in Saint John has a long horizontal crack running parallel to the garage — is this a control joint failure or a sign the sub-base has shifted?

A horizontal crack running parallel to your garage is most likely a control joint failure rather than sub-base settlement. Control joints are intentionally weakened lines cut into concrete to control where cracking occurs — when they fail or are improperly spaced, the concrete cracks randomly, often creating the exact pattern you're describing.

Control joint failure is extremely common in Saint John driveways due to our Maritime freeze-thaw cycles. Your driveway should have control joints cut every 8-10 feet across its width and length, creating a grid pattern of rectangular sections. If these joints weren't cut deep enough (minimum 1/4 the slab thickness), weren't cut soon enough after pouring (within 6-24 hours), or were spaced too far apart, the concrete develops its own stress relief cracks. A crack parallel to the garage suggests the concrete was trying to separate into sections but had no proper control joint to follow.

Sub-base settlement, by contrast, typically creates stepped cracks where one section of driveway sits noticeably higher or lower than adjacent sections. You'd see the crack opening and closing seasonally, with one side potentially sinking or heaving relative to the other. Settlement cracks often follow irregular patterns and may be accompanied by surface unevenness you can feel when walking or driving over them.

Diagnosing your specific crack: Walk along the crack and check if both sides are level with each other. If the crack is simply a clean line with both sides at the same height, it's likely a control joint failure — annoying but not structurally concerning. If one side has dropped or heaved relative to the other, especially if it's more pronounced near the garage or at the street, sub-base movement is more likely.

Saint John's clay soils are particularly prone to seasonal movement. The spring thaw can saturate clay, causing it to expand and shift, while summer drying causes shrinkage. If your driveway was poured over poorly compacted fill or clay that wasn't properly prepared, settlement is possible.

For control joint failure, the crack can be sealed with a quality polyurethane concrete caulk ($8-15 per tube) to prevent water infiltration and freeze damage. Clean out any loose debris, apply the caulk, and smooth it flush. This is a straightforward DIY repair that prevents the crack from widening.

If you suspect settlement, have a concrete professional assess the situation. Settlement issues may require mudjacking ($3-6 per square foot) or poly levelling ($5-10 per square foot) to lift and stabilize the affected sections.

Need help finding a professional concrete contractor? New Brunswick Concrete can match you with local Saint John contractors experienced in driveway assessment and repair through the New Brunswick Construction Network.