Control joint
Control joint turns up in 2 fields: concrete, waterproofing. Here is what it means to the people in each one.
Control joint in concrete
A planned groove or sawcut that makes a slab crack in a straight line exactly where the crew wants it.
Concrete shrinks as it dries and will crack somewhere, so the crew cuts or tools a groove at least one quarter of the slab depth, and the crack forms in the thin section under it. Spacing is commonly held to 24 to 36 times the slab thickness, about 8 to 12 ft for a 4 in slab, with panels kept close to square. Cut too late or too shallow and the slab picks its own crack line.
"Control joints at ten feet each way, and get the saws on it tonight, not tomorrow morning."
Control joint in waterproofing
A cut or formed groove that makes concrete or masonry crack in a straight, planned line instead of randomly.
Concrete shrinks as it dries and masonry moves with moisture and temperature, so builders weaken the section at set spacings with saw cuts, tooled grooves or vertical joints in block walls. The crack then forms below the groove, where it can be sealed neatly. Control joints see smaller movement than expansion joints but still need an elastomeric sealant with proper depth control.
"Saw-cut control joints every 12 feet on the slab, rod them and seal them with the self-leveling urethane."