Acid stained concrete finishes are becoming more popular and frequently being specified for commercial interior flooring finishes. Quite often many people have seen these finishes, not knowing what they are. An acid stain finish is a unique staining process for concrete that results in a natural stone look, which is quite popular for those looking for contemporary or modern living spaces or retail space. You’ve probably seen these acid stained applications in upscale shopping malls, offices, restaurants, retail spaces, casinos, and residences in place of conventional tile, terrazzo, quarry, etc.Acid Stain is not a paint or coating agent, rather, it is a coloring process involving a chemical reaction on a cementitous material. A solution made with water, acid and inorganic salts reacts with minerals already present in the concrete; the result of this reaction is color. Chemical stains can be applied to new or old, plain or colored concrete surfaces. Although they are often called acid stains, acid isn’t the ingredient that colors the concrete. Metallic salts in an acidic, water-based solution react with hydrated lime (calcium hydroxide) in hardened concrete to yield insoluble, colored compounds that become a permanent part of the concrete. There are many manufactures of acid stain and most produce stain in 8 colors that are variations of three basic color groups: black, brown, and blue-green.Acid stains are made from hydrochloric acid, wetting agents and metallic ions. When this solution is placed on concrete it colors the concrete by chemically combining the metallic ions with the particles in the concrete to form oxides. The finish won’t fade or chip-it is permanent. The acid in chemical stains opens the top surface of the concrete (this may be referred to as etched), allowing metallic salts in the mixture to reach the free lime deposits. Water from the stain solution then fuels the reaction. Stain will normally be applied to a surface for 1-4 hours. However, the surface will continue to develop its patina-an appearance of something grown beautiful especially with age or use; established character-for several more hours.
Other factors that affect the outcome include:
• Cement properties and amount
• Admixtures used
• Type of aggregate used
• Concrete finishing methods
• Concrete age and moisture content when stain is applied
• Weather conditions when stain is applied
In general, cements that produce larger amounts of calcium hydroxide during hydration will show more stain color, and higher cement contents produce more intense colors. If they are near the surface, calcium-based aggregates, such as lime-stone, take stain readily and deepen the color of the concrete above them. Solid aggregates, such as gravel, don’t react with the stain.
Acid stains, unlike paints, are not opaque - they are translucent. Some areas will be darker than others, similar to marble or flagstone. Along with the naturally occurring variegations and marbling - any blemishes and imperfections in your concrete simply add character and charm. Even cracks can add to the look.
If you are considering this as a do-it-yourself project, please reconsider. This is not an application that can be learned overnight. You only get one chance to stain a floor. If you are not happy with the result, it will cost more to fix it.
Acid staining concrete chemically & permanently alters the color of concrete while naturally providing mottling and color variance to provide beautiful aged-look finishes. Unlike overlays, which completely covers existing concrete, acid staining is translucent - it will provide rich color, but not cover any existing stains, pitting, or scarred areas of the cement. This process is the least expensive of decorative options, but requires a more pristine surface if a more pristine finish is desired. Yes, ugly stained and pitted garage floors can be brought to life with acid stain. The process will blend in oil stains and discoloration and provide a great looking finish that will hide dirt, prevent salt damage, and be easy to clean and easy to look at. But a beautiful garage floor isn’t a beautiful interior floor or retail space - those spaces require a clean smooth slab if acid stained concrete is the finish of choice. The concrete preparation process required for your floor - either chemical stripping of glue’s or mastic, or mechanical grinding or shot blasting will many times determine whether an acid stain or a thin stained overlay is the best finish to achieve elegant interior flooring suitable for the finest environments. Typically, if a surface can be cleaned without abrading the surface, or chemically stripped, it can be acid stained. If grinding, scarification, or shot blasting is required, an overlay is the best bet so the grind/blast marks are hidden. As a contractor with many years of experience in applying these finishes, you can check out our photo gallery to get some ideas for your own project that you may have in mind.