QUIKRETE® Sand (Topping) Mix, as the name implies, is ideal for topping the surface of existing concrete. Rigorously clean the concrete surface to remove algae, dirt, oil spills and weak or otherwise contaminated surfaces. A high pressure water blasting machine is ideal for preparing the surface. The next step depends on how much you want to build up the surface. If you wish to build up the surface by 1" to 2", apply a coating of QUIKRETE® Concrete Bonding Adhesive, let it dry and then place the Sand Mix (following the directions on the package). If the planned build up is to be about 3/8" to 1", add QUIKRETE® Concrete Acrylic Fortifier to the Sand Mix following the directions on the Acrylic Fortifier bottle (do not use QUIKRETE® Bonding Adhesive in this case). Sand (Topping) Mix can be troweled and finished just like concrete.