Etch & Clean is a concentrated, acidic cleaning solution that uses phosphoric acid to lightly etch the surface and remove mild efflorescence. By using phosphoric instead of muriatic acid, the cleaning agent gently increases the porosity of the surface without damaging the substrate chemicals necessary for subsequent acid staining, thereby allowing better penetration of the stain solution. When fully diluted, 1 gallon makes 5 gallons of ready-to-use product. Clemons Concrete Coatings.