What is a control joint?
A control joint is a planned cut or gap in concrete designed to direct shrinkage cracks into predetermined locations and allow controlled movement as the material cures and expands or contracts with temperature changes.
Control joints are deliberate cuts or gaps placed in concrete slabs to manage how and where the material cracks as it cures and responds to temperature and moisture changes. Unlike random cracks that appear without warning across a floor or driveway, control joints guide shrinkage into straight, planned lines that are easier to maintain and less visible.
As concrete dries after placement, it shrinks slightly. This shrinkage creates internal stress. A control joint weakens the concrete at that line intentionally, so stress is relieved by a predictable crack right there rather than branching unpredictably elsewhere on the slab. The joint typically runs perpendicular to the longer dimension of a slab and is spaced at intervals, commonly every 4 to 6 feet depending on slab size and thickness.
Control joints differ from expansion joints, which allow space for thermal growth when concrete heats up. While a control joint manages shrinkage cracks by directing them, an expansion joint is a gap that physically accommodates expansion. Experienced concrete flatwork providers install both types to keep slabs flat and stable over time, preventing buckling, upheaval, and scattered cracking that compromises durability and appearance.