How the Concrete Acid Stain Works
Stained concrete floors are beautiful, and the color lasts forever. Because it is not a paint or a covering, it doesn't chip off the floor. This type of stain contains phosphoric acid or mild hydrochloric acid. It also contains an inorganic metal salt. The acids open the pores in the concrete, and then the salts react with the chemicals in the concrete to produce color. Depending on the age and porousness of the concrete, the salts are absorbed in varying degrees and produce different shades of color. The finish looks more like marble than a uniform painted finish, and no two floors ever come out the same. After the floor is cleaned and stained, it must be washed with an ammonia solution to clean up the residue left by the acid. Then it is washed again with plain water at least twice. Not only is there an array of color, but you can actually paint a masterpiece on your floor with acid stains.
Water-Based Concrete Stain
The water-based stains are non-acid polymer stains. They also penetrate the concrete to make a permanent finish to the floor. With this type of stain, there is no need for the ammonia solution when you are finished staining; you just wash with warm water and you're done. Maintenance on these floors is as easy and dusting and damp moping once in a while. The water-based stains are said to be the more environmentally friendly stains for concrete. The down side is there are not as many colors to choose from, and they are not quite as translucent as the acid stains. However, once they are sealed, they have a very close resemblance to the acid stain finish.
What Floors Can Be Stained
Almost any concrete floor can be stained, and if it can't, you can put down an overlay that can be stained. This overlay can also be used over some wood floors, too. There are some concrete floors that are not good candidates for acid stain. The most common is the garage floor, where there is a lot of oil, grease and tar stuck to the floor. Although there are some good cleaners out there, some of this residue may already have stained the concrete. There are also some floors that had a curing agent used on them when they were poured. This can stop some of the absorption of the stain, and it will come out very uneven. Some floors are just too badly cracked to stain. You can patch them but the stain ends up showing the patches even more. Small hairline cracks, though, tend to add character to the floor.