Chris Sullivan, a national sales manager for QC Construction Products answered that question for the Concrete Network.

Sullivan divides concrete staining into reactive and nonreactive. ?EUR??,,????'??With a reactive stain, a reaction takes place between the stain and concrete, forming a permanent chemical bond. Nonreactive 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,?EUR??,,????'?? he explains.

Reactive stains can be acid or salt based. Sullivan says acid-based stains have been around the longest and are the ?EUR??,,????'??measure by which all other stains are gauged.?EUR??,,????'?? These stains are inorganic metallic salts dissolved in an acid and water solution.

?EUR??,,????'??A true reactive acid-based concrete stain is translucent, penetrates into the concrete surface, and leaves no film or coating,?EUR??,,????'?? Sullivan specifies.

However, the color palette for acid stains is limited (by nature) to mostly earth tones, which is why most manufacturers offer only eight colors. Nonreactive stains have a nearly unlimited palette of colors and are easy to apply.

?EUR??,,????'??The downside is they lack the deep, rich, translucent color tones only possible with acid stains,?EUR??,,????'?? asserts Sullivan.

Both stain types are viable options, but Sullivan notes: ?EUR??,,????'??Most nonreactive stains require an acid wash to open and prepare the surface to ensure good mechanical adhesion.?EUR??,,????'?? For reactive staining, Sullivan says an acid wash for surface preparation is never recommended, as hydrochloric or muriatic destroys the cement paste at the surface that allows the acid stain to react and develop its marbled color.

According to RandonSeal, which make concrete sealers, reactive acid staining is rather costly and requires neutralizing and rinsing off the acid residue and protecting the surface with multiple coats of sealer.