· By Mateo Haldane · 1 min read
Why concrete cracks (and where we let it)
All concrete shrinks as it cures. The trick is telling it where to crack, and what the cracks you do see mean.
There’s an old saying in our trade: there are two kinds of concrete, the kind that has cracked and the kind that will. It isn’t a failure; concrete shrinks a little as it dries, and something has to give.
Control joints
That’s what the lines in a driveway are for. We cut them a quarter of the slab’s depth, about every ten feet, so the slab is weakest there and cracks in a straight line inside the joint, where you’ll never notice it.
Cracks that matter
A hairline outside a joint is cosmetic. A crack you can fit a coin in, one where one side is higher than the other, or one that grows from year to year means the ground underneath has moved. That’s worth a call.