Q: Do I need to cut completely through a slab to form isolation joints?

A: Isolation joints are meant to allow both horizontal and vertical movement at adjoining parts of a structure. In order to permit vertical movement, these joints need to pass all the way through the cross section of the concrete. Sawing or tooling can't ensure a complete and reliable separation between the concrete elements. Instead, isolation joints should be formed or cast around a full-thickness blockout filled with a material such as premolded fiber strips. Columns can be isolated from floor slabs with circular- or diamond-shaped box outs.