Difference Between Concrete Acid & Stain

Acid-Based Concrete Stain

• Reactive stains contain metallic salts that chemically react with the lime composition of concrete to produce color. The color is determined by the specific variety of metallic salts in the stain. The acidic component of reactive stains -- usually a weak solution of hydrochloric acid -- has no role in the color. It simply induces a mild etching effect to open up the concrete surface. This allows metallic salts to penetrate into the substrate and create a deep, lasting stain. After application, the chemical reaction between lime compounds in the concrete and metallic salts in the stain takes about a month to mature. Once the reaction is complete, molecules in the concrete have been irreversibly altered and the stain is permanent.

Acrylic Concrete Stain

• Nonreactive stains consist of a concrete dye blended with a water-based or solvent-based acrylic. The dye contains penetrants to transport the pigments into pores of the concrete and coat the substrate. Think of it as painting concrete internally. Urethane sealants in the formula lock the dye pigment into the substrate to increase durability. Acrylic dyes can be applied in layers, as in putting successive coats of paint on a wall, to achieve the desired shade.

Relative Advantages

• Acid-based stains offer a depth and translucence not achievable with acrylic stains. Because the color is produced by a chemical reaction at the molecular level, it cannot be worn, washed or chipped away.

  Acrylic concrete stains or dyes are more like paint and are available in a wider variety of standard or custom colors. Because they are fairly opaque, acrylics do a better job of hiding imperfections in the concrete such as stains or variations in density and porosity. Application of acrylics is also an easier one-step process, 60 percent faster than acids. Acrylics require less surface preparation, and they dry in less than one minute after penetrating the concrete.

Relative Disadvantages

• Because they are limited to hues produced by a fixed number of mineral salts, acid-based stains do not offer an extensive palette of colors. They are chiefly available in more subdued, earth-tone shades. Acid staining can also have the side effect of emphasizing imperfections in concrete; its translucence provides little cosmetic cover-up. And the permanence of acid stain, locked in at the molecular level can be a drawback: if you don't like the color or tire of it, you're stuck with it.

  Acrylic stains have a more one-dimensional, paintlike appearance and lack depth. They are basically a coating of the concrete grains and pores, so they do not have the resilience of acid stain, and they will eventually show wear in high-traffic areas. Periodic reapplication of preservative sealers is required to extend life. Also, acrylic-based stains are more vulnerable to ultraviolet light and might fade from exposure to the sun.