To simplify the answer to this question, I’m going to break down concrete acid stains into two families: reactive and non-reactive. With a reactive stain, a reaction takes place between the stain and concrete, forming a permanent chemical bond. Non-reactive stains are tinted coatings, sealers, or dyes that mechanically, not chemically, bond to the concrete surface. Instead, they fill the pores of the concrete surface or produce a colored film or coating.
While reactive stains are available with either an acid base or salt base, acid-based stains have been around the longest and are the measure by which all other stains are gauged. True acid-based stains are made up of inorganic metallic salts dissolved in an acid and water solution. However, Mother Nature limits the color palette for acid stains. That’s why most manufacturers offer only eight colors, mostly earth tones. A true reactive acid-based concrete stain is translucent, penetrates into the concrete surface, and leaves no film or coating.
Non-reactive stains have grown in popularity over the last few years because they offer a nearly unlimited palette of colors and are easy to apply. The downside is that they lack the deep, rich, translucent color tones only possible with acid stains.
While both stain types are viable options for the staining professional. It’s important to be aware that each product requires different procedures for surface preparation. Most non-reactive stains require an acid wash to open and prepare the surface to ensure good mechanical adhesion. Surface preparation for a true concrete stain will NEVER recommend an aggressive acid wash to open the surface prior to application. Applying an aggressive acid (such as hydrochloric or muriatic) destroys the cement paste at the surface that allows the acid stain to react and develop its marbled color variations. A hard-troweled concrete surface, rich in cement paste, is the food on which a true acid-based stain thrives.