Control joint A control joint is a planned groove or weakened line created in concrete to encourage cracking along a predetermined location. It helps manage normal shrinkage as concrete cures.
Concrete naturally develops shrinkage stresses as it hardens. Rather than preventing cracks entirely, control joints direct them to less noticeable and more manageable locations. Proper spacing and depth improve the effectiveness of control joints and contribute to a cleaner, longer-lasting finished surface.
Frequently Asked Questions About Control joint
What is a control joint?
A planned groove or weakened line cut into concrete to encourage shrinkage cracking along a predetermined location.
Do control joints prevent cracking?
No. They do not stop cracks, they direct them to a straight, intentional line instead of letting them wander across the surface.
How deep should a control joint be?
Deep enough to create a genuine weakened plane, commonly about one quarter of the slab thickness. Too shallow and the concrete cracks elsewhere.
What determines spacing?
Slab thickness and mix characteristics. On NYC sidewalks, jointing generally follows the flag layout.