Acid etching is required on bare masonry surfaces like concrete or plaster. It is also effective for removing chalky residue and hard mineral deposits on a previously coated pool. Acid washing opens millions of tiny pores which allow the subsequent coating to penetrate, thus creating a secure cohesive bond. Even on previously coated pools, we heartily recommend an acid wash.
IMPORTANT: To prevent eye injury, NEVER pour water into acid. ALWAYS pour acid into water and wear protective eyewear.
Mixing the Acid
Mix in a plastic bucket a ten percent solution of muriatic acid in water. Most muriatic acid is packaged at 20% or 30% strength. One gallon of 30% muriatic acid mixed with two gallons of water will yield three gallons of ten percent solution. Likewise, one gallon of 20% muriatic acid mixed with one gallon of water will yield two gallons of ten percent solution. One gallon of the ten percent solution is sufficient for etching 100 square feet of pool surface.
The Etching Procedure
Liberally brush the acid solution on the surface. The acid will bubble on the surface when applied. As soon as this bubbling ceases, rinse the solution off with clear water. The surface should feel like fine sandpaper when properly etched. Splash a small amount of water on the surface to see if it is sufficiently etched. If the water soaks in fairly quickly, the surface is properly etched. If the water stands on the surface, another etching will be required or switch to a stronger acid solution. It is of utmost importance that you wash the pool again after etching. The tri-sodium phosphate in the pool washing solution will neutralize all traces of acid left on the surface after etching. After this second washing, allow the pool to dry before coating. However, if you are using Olympic Poxoprime II epoxy primer, you may proceed with priming the pool. Poxoprime II is compatible with wet surfaces. Caution: Do not mix in a galvanized container.