Control Joints

While control joints and expansion joints may sound similar, they serve different purposes in maintaining the structural integrity of a concrete slab.

Control joints are cut, formed or moulded into the slab surface, and are designed to manage the formation of cracks in a singular slab due to either shrinkage of the cement or minor overhead movements.

Expansion joints, by contrast, force a compressible material in between concrete slabs to manage significant movement of the cement from thermal expansion and contraction. By definition, expansion joints are much larger than concrete control joints, and are usually filled with a pliable, strong material such as foam or rubber.

While control joints can be cut into the surface of the concrete after it has fully cured, they may be less effective as a result. Cracks may have already formed in weaker areas of the concrete, particularly if you are working with a large slab. Fixing these cracks is both a more labour-intensive and a costlier process than cutting the construction joints during the curing phase. 

Control joints in concrete help to control the spread and frequency of cracking in the slab. Cracks naturally occur in a concrete surface due to both temperature-based shrinkage and movement on top of the slab. Without a control joint, the slab will crack in random locations. Not only does this look unsightly, it can also weaken the integrity of the concrete. Installing control joints in the weakest areas of the concrete slab controls where these cracks occur. This improves the appearance of the slab and enhances the structural integrity of the concrete over the long term.

You should cut control joints in concrete as soon as the slab is hard enough to be cut safely. Cutting the control joints in concrete that has not fully cured can cause small chunks of cement to chip away from the surface. On the other hand, cutting the joints too late can allow cracks to form naturally in the weakest areas of the slab. It is recommended that you monitor your concrete slab as it cures to determine the best time to cut control joints in the surface.

Control joints are cuts or grooves in a concrete slab, designed to weaken the cement in specific places to control where cracks form. The joints are usually placed at regular intervals across the slab and help prevent random cracking in the concrete when heavy loads cross the cement. Concrete control joints can be saw-cut, tooled or pre-moulded, depending on the type of joint needed.