A trend in the decorative concrete industry is the increased use of water-based stains. These products make it easy to add color to other decorative processes. Unlike acid etch stains, which are dependent on the chemistry of the concrete they are installed on, water-based stains provide more consistent results. Water-based stains include pigments and dyes made from organic or mineral oxide colors. These formulations also may include polymers or silicates to enhance the bond to concrete. Here are how the available systems work.
Topical film-building stains
These stains are opaque in nature—sort of like paint—and reside on the surface of concrete; although their bond is enhanced if they can penetrate the pore structure a little bit. Jack Rigsby, director of research and product development for Proven Performance Chemicals, Bogart, Ga., says the coloring pigment is almost always made with mineral oxides because they don’t degrade in ultraviolet (UV) light; the pigment particle size of the mineral oxides is the largest used in this family of stains. There are a few products on the market, however, made with organic coloring agents that include UV blockers to help protect the color.
Film-building stains also include bonding agents to help them attach to the surface of concrete. Acrylic polymers often are used because they have good bonding properties and moisture vapor in the concrete can pass through. But Rigsby says his company uses lithium silicate for its good bond strength—it chemically reacts with calcium hydroxide in concrete to further increase bond, it forms a hard abrasive-resistant surface, and it’s not soluble in water once cured.
To complete the job, place sealers on topical film-building stains in traffic areas to help prevent oxidation and degradation.
The greatest difference between dyes and pigment stains is that dyes penetrate the surface, allowing some of the look of concrete to remain. This creates a translucentcolored appearance. Jeff Wells, training and business development manager with H&C Decorative Concrete Products, Cleveland, says the coloring agent for dyes is a much smaller particle—even nano sized—and it does not require bonding agents. Carl Cabot, vice president of new product development for Ameripolish, Lowell, Ark., adds that most dyes form solutions in water, not suspensions. They go into solution in water in the same way that sugar or salt does.
Preparation for stains
All stains must either bond to the surface of concrete or penetrate into the surface. The first step is to consider the mix design of the concrete; it should develop enough capillary structure for stains to penetrate. If you aren’t the one placing the concrete, discuss the idea of using a mix design that isn’t extremely dense with those responsible.
Concrete surfaces mustn’t have any coatings on them—curing agents, sealers, or adhesives. Even with no coatings, they must still be prepared so that stains and dyes can bond and penetrate. Wells recommends using 15% phosphoric acid solution to lightly etch the surface. “It’s comparable to sanding with 120-grit sandpaper,” he adds. “It rinses off with water without leaving an acid residue and becomes a fertilizer for surrounding landscape material.”
Cabot says they recommend using floor buffing machines with carbide impregnated brushes to provide an aggressive, physical cleaning. He advises using dyes and stains only on 800-grit or more diamond polished concrete.