Acid staining
Acid staining is not a dyeing or pigment-base coloring systems, but a chemical reaction. A mixture of water, salts and acid is applied to the concrete surface and later neutralized by a basic solution of ammonia and water. This chemical reaction with the existing minerals in the concrete creates new colors on the concrete surface. Due to inconsistencies in the surface of concrete, acid staining creates a variegated or mottled appearance that is unique to each slab. The thickness of this color change ranges from 1/16th to 1/32nd of an inch. Exterior concrete surfaces may not color as well as interior surfaces because the environment has leached or percolated out the mineral content.
Chemicals commonly used in acid staining include Hydrochloric acid, Iron chloride and Sodium bicarbonate.