Joint (Control Joint)

A control joint is a groove — tooled while the concrete is plastic or saw-cut shortly after finishing — that creates an intentionally weakened plane in a slab. As concrete shrinks while curing, it cracks at the joint instead of randomly across the surface.

Spacing and timing both matter: joints cut too late, or spaced too far apart, won't reliably catch shrinkage cracking. A common rule of thumb is joint spacing (in feet) of roughly 2 to 3 times the slab thickness (in inches).