Even though water-based stains aren't new, the technology is constantly improving, and these stains are taking decorative concrete in new directions. When used by concrete artisans, unique effects can be achieved. Several of the presenters at the Artistry Demos at the 2005 World of Concrete used water-based stains and got interesting results (more about this in the April issue).
The color range possible with water-based stains exceeds that of chemical stains, although sometimes they are used together. Water-based stains aren't paints—their particle size is much smaller than that of paint— and they are formulated just for concrete. Chuck Brunner, the owner of Smith Paint Products, Harrisburg, Pa., says that “stains offer both more control of color and a much wider range of color possibilities than other concrete coloring systems.”
H&C Concrete Products, Cleveland, in the early 1980s, was perhaps the first company to develop water-based stain technology (it is now part of Sherwin Williams). Its original product was a combination of styrenated acrylics, pigments, and other materials in a water base. Today many companies produce these stains.
Every company that manufactures water-based stains has its own formulations and proprietary ingredients. But several common generic compounds are used, including the following:
- Acrylic resin. Acrylics are increasingly the primary resin used. They are insensitive to ultraviolet (UV) light, so they don't color fade. They also have the greatest water vapor transmission capability of the resins used for sealers and coatings. Their use can greatly reduce the risk of delamination on slabs that have moisture problems.
- Styrene resin. Pete Donati, Product Brand Manager for H&C Concrete Products, says that his company doesn't use these resins anymore because they yellow when exposed to UV radiation. Some other companies still do use styrene, though, because it provides hardened films with good water resistance.
- Color pigment. Pigments include a wide range of coloring agents, from inorganic metallic oxides to organic coloring tints and pigments.
- Coalescing agents. There are many different coalescing agents that serve to separate the sticky molecules of resin while the product is being stored and applied. After application, most of the coalescing agents evaporate. Brunner says there is currently a movement in the industry to reduce the amount added to stains and someday to eliminate them. The reason is to reduce the VOC component of the final product, but he notes that some coalescing agents never fully leave the stain after application.
- Glycol. Glycol is added to some products to reduce skimming problems.
- Water. As the highest percentage ingredient, water makes it possible to apply the resin as a film.
How the stains work
As is the case with all water-based sealers, there is a sequence of events when stains are applied to concrete. First, the water in the stain must evaporate or be absorbed by the concrete. Next, the coalescing agent begins to evaporate, allowing the molecules of resin to stick together, forming a film. As this happens, the pigment becomes permanently embedded in the resin. Problems occur when the coalescing agent evaporates before the water does—which can happen when slab or ambient temperatures or humidity conditions aren't right. Donati says the ideal situation for stain application is when temperatures are near 70° F and the humidity is about 50%. “When you try to install these products under extreme conditions, both the bond and the resulting film formation can be compromised, resulting in a difficult removal situation.”
Preparation and application
Water-based stains are intended for concrete surfaces that have a pH between 6 and 10. This means they work better under alkaline than acid conditions. Surfaces must also be porous enough to allow the stains to penetrate and bond. For horizontal surfaces, Donati and Brunner recommend a mild acid wash, neutralized afterwards to restore the higher pH. Vertical surfaces can be pressure washed with a 4000-psi pressure washer (hold the nozzle about 4 inches from the concrete) to remove laitance and produce some porosity. When a slab is fully cured and dry, stain can be applied by a variety of methods including airless sprayer, paint roller, or brush depending on the desired appearance.
Water-based stains have fairly good abrasion resistance, but in high traffic areas, clear sealers should be applied to the wearing surface and replaced as needed. Check with the specific manufacturer for sealer recommendations.