Saw-cut joint depth guideline is to cut to approximately what percentage of slab thickness?

• A. 10%
• B. 15%
• C. 20%
• D. 25%

Answer: (D)

Saw-cut joints are placed to control cracking by creating a deliberate plane of weakness where a shrinkage crack can form. The depth needs to be enough to guide the crack along the joint while keeping most of the slab’s strength intact. Cutting to about 25% of the slab thickness hits that balance: it’s deep enough to reliably intercept cracks along the joint, but not so deep that it weakens the slab or risks other problems. Shallow cuts often don’t control cracking well, while deeper cuts don’t provide proportional benefits. So the standard guideline is roughly a quarter of the slab thickness (for example, 1 inch deep in a 4-inch slab, 1.5 inches in a 6-inch slab).