Mix the acid stain mixture outdoors or in a place with good ventilation. Hydrochloric acid is the main ingredient in the staining mixture, so wear all protective gear recommended by the manufacturer. When mixing the acid stain, always add the acid stain to the water rather than water to acid. Pour the mixed acid stain into a two gallon pump with all the plastic parts. It is important that there be no metal on the applicator or spray wand because hydrochloric acid is corrosive to metal. For hand trowelled floor, dilute the stain with water using a ratio of one part stain to four parts water. For machine-trowelled floors, the mixture will be more concentrated at a ratio of one part stain to one part water. Adding water will also allow you to control the depth of color. Test the sprayer outside to ensure a nice even flow before using it inside.