Acid Stained Concrete
"Reactive Stain" is a process of applying an acid on top of bare concrete, cement or overlay material to cause a chemical reaction that changes its color appearance. This appearance is controlled by the purity of the solution applied.
"Non Reactive Stain" is more so a translucent dye that is applied to a surface to add or enhance the color of that surface. It can also be diluted to lighten its effect.
The process of creating acid stained concrete is easy to explain but difficult to tightly control. We apply a water-soluble acid solution to the surface of the concrete. It will penetrate down to 1/4 inch (6 mm). In this depth, a mineral called lime, or calcium hydroxide, lays dormant as part of the materials that always make up concrete. When the stainer introduces a mixture of special metallic salts, they flow through the porous surface and change the lime through a chemical reaction.
The stages of staining depend on many uncontrollable circumstances, such as the aggregate material in the cement, types of acid and salts, amount of water, temperature and humidity, age of old cement, and the method of sealing and buffing. This organic evolution and unpredictable outcome is part of the appeal of acid stained concrete to many installers and consumers.
Over the next few hours, as the mixture cures, the color will emerge. Eventually that shade will settle as a permanent addition to the chemistry of the concrete. However, the color may evolve and age for up to a month. For those concerned about controlling or anticipating the final color, you could try applying the acid solution to a hidden part of concrete, such as underneath a cabinet for a floor or where a cushion may go for a bench. The resultant colors are usually in the family of brown, green, and tan.