Pool surfaces MUST be completely clean and free from slime, scum, body and suntan oils, algae, calcium, and other surface residue before they can be satisfactorily coated or recoated. Coating will not bond to contaminated surfaces. If you apply over any surface residue or foreign matter, it (the foreign matter) will soon disintegrate and fall away from the surface taking the coating with it. New and old plaster and bare poured concrete pool surfaces must be clean and free from oil, grease, silicone, or wax type releasing agents before they can be etched. Pools are prepared for coating by a three step procedure: (1)WASHING (2) ACID ETCHING and (3) WASHING. Pools are scrubbed easier by using Olympic No. 910 Pool Washing Comound, use No. 910 Pool Washing Compound before and after acid etching.