What is Acid Stain?

 

Acid stain is an aqueous solution used to color existing concrete which is known as acid staining. Acid stain has been around since at least the 1920’s. It adds color that will never fade, chip or peel. It is absolutely permanent. Let’s talk about the components in acid stain for a moment. Water. We all know what water is. In acid stain, water is basically the carrier. Everything is added to the water. Hydrochloric acid which is also known as muriatic acid or HCL brings down the ph of the acid stain solution. It does other things in the acid staining process that we will talk about in a bit. Metallic salt compounds such as manganese, copper sulfate and cupric chloride to name a few are what determines the color. The more mineral salts that are added; the darker the stain.

 

How does it work?

 

So, how does this create color in an existing concrete slab? That is a very complex process for such a simple product. When acid stain is applied to concrete it reacts with calcium carbonate and calcium hydroxide (CH). This reaction causes the stain solution to move toward a neutral pH. The strength of the acid must be just right: If it’s too strong the reaction won’t go forward and if it’s too weak the metallic hydroxides or oxides will settle to the bottom of the container. While the acid is reacting with calcium compounds in the concrete, the water and metallic salt solution penetrates into the surface of the concrete. With the acid neutralized, the pH of the acid stain solution rises, causing the metallic hydroxide or oxides to precipitate out of the solution and become a solid. At the same time, the metallic oxides react with the CH in the concrete to bring out the finished color.

 

Where is acid stain used?

 

The most popular use for acid stain is coloring interior concrete floors. It creates an old world look that is very mottled and variegated throughout the concrete slab. Both residential homes and commercial businesses alike that have concrete flooring are ideal candidates for the beauty that acid stain can create. Acid stain colors are very limited. There are usually 8 standard colors which are gold, tan, brown, red, black, umber, blue and green. But for the most part your options are some shade of blue, green, brown and tan. Although acid stain these days is thought of as laborious and time consuming; it does not look like it will be pulled from the bag of tricks just yet. It has proven itself as a very long lasting and beautiful option for coloring existing concrete.