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Color Hardeners
A dual-purpose application
by John Strieder
needs a tough, easy-to-repair coating on a hotel or apartment walkway, he starts scattering the color hardener. “It becomes very, very hard,” says Smith, based in West Hills, Calif. “It becomes a very, very wearable surface. It almost becomes like an eggshell finish.”
Like other concrete craftspeople, Smith still values hardener for its original function: making a concrete surface more durable and resistant to heavy traffic and other abuse.
But for a growing number of contractors, color hardeners aren’t just for hardening anymore.
“I’d say the balance of interest has gone from hardening to the dry-shake color aspect,” says Steve Johnson, marketer with Solomon Colors.
In the age of decorative concrete, the allure of “dust-on” has as much to do with its coloring properties as its ability to harden. Color hardener can, in fact, be purchased in just about any color a contractor can imagine, including uncolored. “We stock 40,” says Debbie Bliss of RAFCO Products, maker of Brickform color hardeners, “but we can make any color in the rainbow.”
Hardeners have other practical applications in decorative work, too. When stamped, their dense surface holds clear, sharp impressions. They are also used as lighteners, covering gray concrete with a more workable shell of a lighter color.
Color hardeners are made from cement, sand and pigment, with finishing agents, wetting agents or retardants added to suit manufacturers’ preferences.
The most common pigments are iron oxides. Contractors pay more for cobalt oxides, used in blues, and chromium oxides, which make greens. Titanium additives are used for whites and to lighten colors. “Organics” can make quirky colors such as ultramarine.
But the most important element in color hardener isn’t the pigment, says Joe Garceau, co-owner of Butterfield Color Inc. It’s the sand.
Quality sand should be hard and clean, he says. The grains should have angular shapes or hard edges like crushed quartz, not be round like silica. “Round aggregate doesn’t have good finishing characteristics,” he says. “The surface does not close as well. They don’t nestle into each other. They just continue to want to move as you trowel them closed.”
Another big factor is gradation, Garceau says. Most manufacturers’ sand mix recipes are proprietary, he says. “That is the secret. Everybody can buy cement.”
Hardener is usually scattered across a surface by hand or by brush, although machines are available for big commercial jobs. Water in the wet concrete bonds with the cement in the hardener after troweling.
The material is applied in two sweeps with spot follow-up, using about two-thirds on the first pass. The recommended coverage rate for Brickform is 60 pounds for every 100 square feet of concrete, Bliss says. With light and pastel colors, contractors may need to use more, she says, as much as 90 to 100 pounds per 100 square feet.
Distributing hardener is something of a skill. “How do you keep it even? You get good at it,” Garceau says.
Put it on too early, Bliss says, and it will not allow moisture to escape from the curing concrete, causing the solidified hardener to peel away. Wait too long, and the color will not be worked in properly, resulting in blotchy color.
Use too little, and either the gray will show through the hardener or foot traffic will wear it off. “I’ve never had a thickness problem,” Smith says. “I’ve had numerous failures not having enough. The secret to dust-on is, thicker is better than thinner.”
And if the dust-on is troweled before it becomes uniformly wet, lumps form, Johnson says. |
