How do you check that control joints are cut to the correct depth?

• A. Ensure joints are at least 1/4 the slab thickness (or per project spec) and that the cut reaches the depth to relieve tensile stresses.
• B. Joints should be cut at half the slab thickness.
• C. Joints can be any depth.
• D. Joints should be about 5% of slab thickness.

Answer: (A)

Control joints are cut to give concrete a planned cracking path that relieves tensile stresses from shrinkage and temperature changes. The standard way to check depth is to confirm the groove reaches at least one-quarter of the slab thickness (or as specified in the project). After sawing, measure from the surface down to the bottom of the cut with a tape, ruler, or depth gauge and ensure it is at least thickness divided by four and runs the full length of the joint. If the cut is shallower, it won’t reliably relieve stresses; deeper cuts aren’t typically needed and can introduce unnecessary issues. The approach of cutting to a random or much smaller depth won’t provide proper control of cracking.