What is the difference between a control joint and an expansion joint?
A control joint is an intentionally weakened break in a concrete surface to allow for contraction stress. These joints are most often seen in concrete slabs. Often these joints are cut after the concrete is poured, using a concrete saw. The concrete is generally scored only, not cut all the way through. This allows the concrete to naturally crack at a joint and not elsewhere in the slab. Control joints are often constructed to transfer lateral loads across the joint. Expansion joints, on the other hand, are true structural joints separating different sections of the building typically used to accommodate thermal and moisture expansion in concrete. An expansion joint is a joint, left completely free of mortar and filled with elastomeric sealant to keep it watertight. Concrete expands over time.
