When should control joints ideally be placed in concrete?

Control joints play a crucial role in managing the cracking that can occur in concrete slabs as they undergo shrinkage and temperature changes. The ideal time to place control joints is before the concrete hardens. This timing allows the joints to effectively guide the cracking in predetermined locations, minimizing random cracks that could compromise the slab's integrity.

If control joints are placed after the concrete has set, the benefits of directing the cracks are lost. Waiting until after pouring could lead to increased difficulties in achieving clean and precise joints, and the effectiveness of the joints would be diminished since the concrete would have already started to shrink and crack. Placing them before the concrete hardens ensures that they are integrated into the slab structurally and can perform their function effectively. This proactive approach is essential in flatwork finishing to maintain the longevity and durability of the concrete surface.