Prepare the surface by removing all dirt, curing compounds, sealers, mortar, etc. In most cases a wire or nylon brush will do the job. Residue from persistent chemicals such as curing compounds or sealers can be removed by bead blasting or sand blasting. Substrates should be true within 1/8" (3mm) in 8 feet (2.4m) for walls and 1/8" (3 mm) in 10 feet (3 m) for floors. Before leveling a surface, wash dry or dusty surfaces and remove excess water.
Compounds that may be needed to adequately prepare the surface include a leveling mortar acrylic compound (to correct surfaces that are not plumb and level), a substrate build-up product, and a patching product.