The original ZipStrip control joint is a rigid polystyrene extrusion that creates a straight line, controlled crack on the surface of all on grade slabs. ZipStrip eliminates random cracking in all variations and thicknesses of slabs where a control joint is required. ZipStrip is the economic alternative to saw cutting to create similar straight line surface joints. ZipStrip is inserted in the concrete when the concrete is still wet, preferably after screeding and tamping. A straight vertical line of weakness is formed where ZipStrip was inserted. The top portion of the ZipStrip is removed leaving the vertical portion in the concrete to form a weakness in the surface of the slab to the ground. The new joint can be tooled with a radiused edger or the surface of the slab can be finished over the top of the joint. As the slab shrinks during the normal curing process a slight straight line separation on the surface of the slab will appear where ZipStrip was inserted.