09/01/2026
Those lines running across your driveway or patio aren't random—and they aren't signs that something went wrong.
They're called expansion joints (and in some cases, closely related control joints).
Concrete naturally expands and contracts as temperatures change. It also shrinks slightly as it cures. If there's nowhere for that movement to go, the slab can crack unpredictably.
These joints create intentional locations for movement, helping reduce the chance of large, random cracks across the surface.
It's a great example of something I love about construction:
The best builders don't assume materials won't move.
They design for the movement.
The next time you walk across a driveway, look down. Those simple lines are quietly doing one of the most important jobs in concrete construction.