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If acid staining a pre-existing concrete floor, remove all baseboards and trim work that might be damaged by the stain mixture.
Cover the walls using 12-inch masking paper, to protect your walls from discoloration during the acid staining process (Image 1). Cover all the walls and exposed lower cabinets. To attach the masking paper to the wall, wrap the painter's tape around your finger so that both sides have adhesive on them. Tack a piece on the wall every 6 to 8 inches. Pull the paper tightly across the wall, and secure the paper on the top every 12 inches with another piece of painter's tape. Remove the knobs on bottom cabinets and cover the metal screws with painter's tape (Image 2).
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.
When applying the acid stain to the floor, keep the spray wand about 18 inches above the floor. Spray in a random pattern and get the floor thoroughly wet, but without puddles. The acid in the stain reacts with the lime deposits in the cement floor giving it multiple hues. Areas where there’s more lime in the cement will render darker hues of color. Allow the first coat to dry completely for about an hour, and then apply a second coat. Repeat this process until the floor reaches the desired color.