Chemical stains are water solutions and metallic salts that penetrate and react with concrete to provide insoluble, abrasion resistant color deposits in the porous concrete. They contain a diluted acid to etch the concrete surface slightly and to remove any surface laitance so that the staining ingredients can penetrate deeper and react more uniformly. Stains are applied to surfaces of cured concrete that are at least one month old and free from all foreign matter.
The chemicals used limit concrete stain colors. Black, green, reddish-brown and various shades of tan are most widely available. The color is not merely a surface coating, but penetrates to a limited depth and will not chip, crack or peel. However, it can wear away to the extent that the concrete surface does. In high traffic areas, it is a good idea to maintain stained concrete with periodic applications of colored wax or concrete sealers.
Applying stain to flagstone sculpture, board formed, and many other texture designs have made interesting and unusual applications. Colors of the stained surfaces will vary in shade, as do natural rocks, depending on porosity, age and chemical composition of the concrete. The resulting patina effect is unique and cannot be duplicated with other coloring materials. Stains have enhanced specially formed concrete zoo displays, fountains and other decorative projects. Exposed aggregate slabs or panels can be stained without affecting the color of most aggregates.