What is an Acid Stain?
Just as the name implies, acid concrete stains use acids to etch and help transform the color of concrete. Either phosphoric acid or hydrochloric acid will be used, in addition to metallic salts, to cause chemical reactions in the surface of the concrete. These chemical reactions cause changes in the color of the concrete that cause the surface to look like natural stone or marble, which makes this a favored method among designers and homeowners.
The downside to using an acid concrete stain is the unpredictable nature of the product. You might think that the stain would react similarly every time that it is exposed to concrete, but there are many factors that can influence the reactions that take place. Everything from the age and porosity of the concrete, and the climate where the stain is being used, can affect the shades that are produced.
It can take many hours for the concrete to achieve the desired color; therefore, it is important not to be discouraged if the concrete does not look as desired immediately after the acid stain is applied. Once you are happy with the color, the acid must be neutralized and the floor washed of any residue before concrete sealers are applied.
Using Water-Based Stains or Dyes Instead
Water-based stains are increasing in popularity because they are more predictable and do not rely upon any chemical reactions to produce color. These water-based alternatives apply more like paints or wood stains and can produce more uniform color or opaque colors. The porous concrete absorbs the water, allowing the stain or dye to settle into the concrete, providing a permanent coloring.
Mixing the Two Together
In some cases, contractors will choose to use the combination of an acid stain with a water-based concrete stain. For example, a water-based stain could be used to provide a consistent uniform and predictable color, and the acid can be used to provide accents that make the surface look more like natural stone. Or the other way around depending on preference. It is wise to experiment with your concrete color supply and to test your possibilities.