Staining concrete both inside and outside has become a popular way to enhance the look of finished concrete. Staining imparts a luxurious richness that can’t be achieved by any other coloring medium. Rather than produce a solid, opaque effect like paint, stains permeate the concrete to infuse it with luminous, translucent tones that vary depending on the surface they are applied to and the application techniques used.
Stains for concrete come in two general categories: acid-based chemical stains and water-based acrylics. Most acid stains are a mixture of water, hydrochloric acid and acid-soluble metallic salts. They work by penetrating the surface and reacting chemically with the hydrated lime (calcium hydroxide) in the concrete. The acid in the stain lightly etches the surface, allowing the metallic salts to penetrate more easily. Once the stain reacts, it becomes a permanent part of the concrete and won’t fade, chip off or peel away. The palette for acid-etch staining is generally limited to earthy tones, such as tans, browns, terra cottas and soft blue-greens.
If you want to go beyond the subtle drama and subdued earth-toned palette of acid staining, consider using water-based stains, which come in a much broader spectrum of hues. Most manufacturers offer dozens of standard colors, including black and white and even metallic tints. Like acid stains, water-based stains (typically a blend of acrylic polymers and pigments) penetrate the concrete to produce permanent color, ranging from translucent to opaque depending on the product.