A control joint is a groove or gap intentionally formed or cut into concrete, stucco, or similar materials at planned intervals, specifically designed to create a weakened point where shrinkage cracking will preferentially occur, directing what would otherwise be random, unsightly cracking to a planned, less visible location instead.
Unlike an expansion joint, which specifically accommodates ongoing thermal movement, a control joint primarily addresses the shrinkage that occurs as concrete or similar materials cure and lose moisture, a process that happens largely within the material’s first weeks and months.
Proper control joint spacing, calculated based on the specific material and application, significantly affects how well this technique actually succeeds at directing cracking to the intended locations rather than having cracks appear randomly elsewhere despite the joints being present.
What Does a Control Joint Involve?
- A groove cut or formed into the material during installation
- Placement at calculated intervals based on the material and application
- A weakened point encouraging cracking at that specific location
- Sometimes filled with sealant for water resistance
Why Are Control Joints Important?
By directing inevitable shrinkage cracking to planned, less visible locations, control joints significantly improve a finished concrete or stucco surface’s appearance compared to allowing random, unpredictable cracking to occur wherever internal stress happens to concentrate during the curing process. This proactive approach to managing an otherwise unavoidable material behavior produces a considerably better finished result.
Because control joint spacing requirements are based on established industry guidelines specific to the material and application involved, following these standards rather than guessing at appropriate intervals significantly improves the technique’s effectiveness at actually controlling where cracking occurs.
Control Joint vs. Expansion Joint
A control joint manages shrinkage cracking during a material’s curing process. An expansion joint accommodates ongoing thermal and moisture-related movement throughout the material’s entire service life, addressing a different, longer-term movement concern than the shorter-term curing shrinkage control joints manage.