Concrete Countertop Solutions SPB-001-S 64' Square Edge Poolform Backing Kit. The Square Edge Poolform Backing will replace the existing Poolform Backing (piece included with Poolforms that is used to hold the form liners in place). It is notched to bend and is compatible with straight or bendable forms. This will eliminate the need for a Poolform Liner and save money on jobs using a flat square coping edge. Casting against the smooth PVC form will give you a polished 3" square edge with a 1-1/2" overhang.