What are isolation joints?
Control joints are constructed (either sawed or tooled) to create planes of weakness in the concrete so that cracks will occur at the desired location. Remember the rule of thumb for control joint spacing is 30 times the thickness of the slab. Another rule is that joints should be cut one quarter of the depth of the slab. Keep in mind that were trying to make the concrete crack in the joint and proper depth of the cut helps insure this. Isolation joints are used to separate or isolate slabs from other parts of the structure such as walls, footings or columns and driveways and patios from sidewalks, garage floors, light poles or any other obstruction. Isolation joints permit movement of the slab and help minimize cracking caused when movement is restrained. Random cracks will often occur off of floor drains or posts. Ideally, isolation joints would be employed in these situations. If you feel it is not practical to use isolation joints, be aware that these are areas prone to cracking. A
