Random cracks in concrete slabs have been a fact of construction life since the first batch of concrete was placed and finished. Because such cracks are invariably unattractive, often unsanitary and eventually necessitate costly repair work, a variety of crack control measures have been developed and tried. A new crack control tool, pioneered in California, consists of a pre-formed T-shaped plastic contraction joint which is inserted into wet concrete at specified intervals. Successful use reportedly does not require any special skills, timing, weather conditions, or other hard to control factors. It is said to be suitable for concrete floor slabs, sidewalks, alleys, walkways, parkways, malls, patios, lightweight balconies, driveways, and certain highways. For best results with the plastic contraction joints in slab on grade floor construction, concrete should be placed in forms in appropriate bay widths, generally not exceeding 20 feet. After screeding, a plant or bridge the same length as the bay is placed across the forms perpendicular to the length of the bay at column intersections. One man, walking across this plank or bridge, can push a No. 750 straight-edge tool down into the freshly placed concrete in a straight line so the control joint may be inserted. The joint, which comes in lengths from 4 to 20 feet, is pushed into the cut using a sawing motion until the upper surface of the pull-top stiffener is flush with the concrete. The stiffener is then peeled off. The concrete is finished in the usual manner, the plank or bridge is moved down to the next column intersection, and the process is repeated.