…continued from previous page
Release Agents
Both powders and liquids have their advantages
by John Strieder
for liquids, as can cold, damp weather, McMahon says. “It all depends on the moisture level of the concrete. The surface has to be drier for liquids to work.”
But he uses liquids whenever he can, tinting them as needed, because they make for a much cleaner job, he says. “Liquid release is so much easier to use,” he says. “Powder is so fine that it becomes airborne. It adheres to stucco and plaster. It gets everything covered in color.”
Overlays are more controlled in terms of moisture levels, so liquid release works well on those jobs, he adds.
Powder release agents are composed of cement, iron oxide pigment for color, and moisture repellant that keeps the water in concrete from clinging to the stamp. It’s applied after the concrete slab has gelled but before final troweling.
Luckau recommends you sift the fine powder by hand before application to break up clumps. “It feels almost like silky water,” he says. “It’ll really fluff up.”
Broadcast the powder in an even coat, and stamp right away, Luckau says. The powder should be thrown sidearm, like skipping a rock across a lake. But for even better results, he says, whisk it sidearm with a 2-inch by 6-inch masonry brush. A bucket of release will last longer that way. “The powder will stick on the brush just like paint. It’ll just float right over the concrete.”
Using a brush will also help you avoid clumping, Branum says. The powder doesn’t throw as naturally as, say, aggregate-based color hardener. If you stamp a clump instead of concrete, you’ll be left with a bare spot.
With release, you want 100 percent coverage, he adds, not 60 percent to 65 percent like with color hardener.
Leave the powder on for two or three days after stamping, Luckau says, so the color gets a good bite into the surface. That way, you won’t wash the color away when you finally come back to clean off the powder.
Liquid releases, for their part, are solvents mixed with mineral spirits. CemTec’s liquid release is sold as a concentrate, with adding mineral spirits left to the contractor. It includes a fragrance to offset the smell.
Contractors have been tinting the clear, oily substance on their own for years. But Branum warns that there are no standards for this practice. “I wouldn’t say anybody has come up with a proper system for doing it,” he says.
When applying liquid, use a sprayer to coat the surface just ahead of the area that is being stamped. Don’t treat the whole slab at once, because the release will evaporate before you finish.
Most contractors fog both the mat and the concrete, Cook says. Texture mats are more forgiving than brick or cobblestone stamps, he says, so fog the latter more often.
“As long as you can’t see the concrete through it, it’s thick enough,” Luckau says.
If it’s a little uneven, don’t worry, Branum says. The worst thing that can happen is your stamp sticks a little. Then, you just fix it. “You don’t want to overapply,” he says. “You want to have a nice even coat on the surface.”
It’s also important to note proper stamping times, he says. If the concrete is too wet, it will cling to a stamp even after the application of release.
Whether powder or liquid, McMahon says, use as little as you can. “You don’t want too much powder because it takes away from the definition of the stamp,” he says. “You don’t want too much liquid because you don’t want to liquefy the surface. If the surface comes up, you have one of two things — too little or too much. A lot of guys put down more and more, and they are only making the problem worse.”
Many liquid releases take a while to dry, he adds, even to the point where you can’t cure-seal the job on the same day. “It needs to completely evaporate first,” he says.
Powder releases that are lighter than the base color can change the hue of the slab, Luckau says. Lay a film of light gray over red, for example, and you can end up with pink. Darker releases are required for antiquing and shadowing — say, dark brown, black or charcoal gray for a red base. “It’s like makeup,” he says. “A lady who wants to cover up things uses light. If she wants to bring out her cheeks, she uses dark.”
But a layer of lighter release can be buffed, McMahon says. Going over the surface afterward with a scrubbing machine, or simply letting wear and tear do the work, will allow the original color to bleed through. “You get a cool effect that way,” he says.
|
