What is acid etching?

Acid etching or acid staining is the addition of hydrochloric acid, and acid-soluble metallic salts to concrete during the curing process. Despite the term "acid etching", acid is not the ingredient that colors the concrete. The metallic salts in the acid, water base solution react with hydrated lime in hardened concrete. The result is insoluble, colored components that become a permanent part of the concrete.

As the acid stain reacts with the concrete it lightly etches the surface. Acid etching can be done on natural concrete or dyed concrete for a more subtle effect. Brushes and sponges are often employed during the acid etching process. An acid etched surface is permanent and will not fade or peel off.

Every acid etched surface has a unique character with diverse variations of color and intensity. Mottled colors often mimic textures and patterns found in nature. It is not uncommon to be reminded of marble or lichen when looking at an acid etched surface.