Concrete problems

Nobody tells homeowners this before the pour, which is why cracking feels like fraud when it appears. Concrete shrinks as it dries. If that shrinkage is restrained, tensile stress exceeds the concrete's strength and it cracks. Joints are simply pre-planned cracks — NRMCA's phrase — placed where you can tolerate them.

Plastic shrinkage cracks show up in the surface within hours of placement, while the concrete is still plastic. NRMCA describes them as roughly parallel, on the order of 1 to 3 feet apart, relatively shallow, and generally not reaching the slab perimeter. They are unsightly but rarely impair strength. They happen when surface water evaporates faster than bleed water can replace it — wind over 5 mph, low humidity, or high temperatures.

Scaling is flaking or peeling of the finished surface, caused by freeze-thaw cycles, made worse by deicing chemicals. Moderate scaling can take off 1/8 to 3/8 inch of surface mortar. NRMCA attributes most scaling to non-air-entrained concrete or too little entrained air, low strength, excess water, over-finishing, or insufficient curing. That is a workmanship and mix problem, not bad luck.

Crazing is a fine web of shallow surface cracks and is cosmetic. Settlement cracks and cracks with one side sitting higher than the other point at the subgrade, and that is a real defect worth pursuing.

How to choose

Check whether the crack is at a joint

A crack that followed the sawcut is the joint doing its job. A random diagonal crack across a panel usually means joints were spaced too far apart, cut too late, or cut too shallow.

Measure joint spacing before you argue

NRMCA recommends 24 to 36 times slab thickness — about 10 feet for a 4-inch slab — with 15 feet as a maximum, and joints cut to at least 1/4 the slab thickness. If your 4-inch driveway has joints 20 feet apart, that is documentable.

Look for vertical displacement

A flat hairline crack is cosmetic. One side sitting higher than the other means movement below the slab. Different problem, different fix.

Photograph and date everything

Take photos on day one, week one, and each season. A crack that is stable for two years is a very different conversation than one that keeps opening.

Scaling in the first winter is a red flag

NRMCA advises avoiding deicing chemicals in the first winter entirely. If a new slab scaled after one season of salt, ask whether the mix was air-entrained and at what strength.

Don't accept "all concrete cracks" as the whole answer

It's true, and it does not excuse missing joints, a frozen or uncompacted subgrade, water added at the truck, or no curing.