Here is the part most homeowners have never been told: concrete cracks. It is not a matter of if, it is a matter of where and when. The job of the contractor is to control that crack.
Why Concrete Cracks
As concrete cures, it shrinks. A 20-foot slab shrinks about a quarter of an inch as it loses moisture in the first 30 days. That shrinkage is a tensile stress the concrete cannot resist. Unless we give it a place to go, it goes wherever it wants.
What a Control Joint Does
A control joint is a shallow saw-cut that creates a planned weak line in the slab. When shrinkage stress builds up, the slab cracks underneath that line instead of randomly across the surface. The crack is still there. It is just hidden inside the saw-cut, exactly where we intended.
The Twelve-Hour Window
Saw-cuts have to happen between 4 and 12 hours after the pour depending on temperature and mix. Too early and the edges ravel. Too late and the slab has already cracked on its own, random and visible. We track each pour and return at the right window with a walk-behind saw.
If your driveway has a crack snaking across the middle instead of a straight saw-cut, ask when your contractor cut the joints. If the answer is “the next day” or “we did not,” you are looking at the reason.