Acid stain is not a dyeing or pigment-base coloring systems, but a chemical reaction. A mixture of water, mineral salts and a slight amount of muratic acid is applied to the floor. This chemical reaction with the existing minerals (primarily lime) over a period of one to four hours creates new earth tone colors on the floor. The floor is later scrubbed to remove excess stain and neutralized by a basic solution of ammonia and water or baking soda (less likely to cause whiting later) to help raise the ph level back to normal level. Due to inconsistencies in the surface level of concrete floor, acid staining creates a variegated or mottled appearance that is unique to each stained slab. The color penetration ranges from 1/16 to 1/32 of an inch. Older exterior concrete surfaces may not color as well as interior surfaces because the environment has leached or percolated out the mineral content. As well, any exposed aggregate (rocks) in worn concrete will not accept staining.