Concrete's Changing Colors
A behind-the-scenes building material turns into a kitchen star. Here's a look at how a concrete counter is made
Hear the words "concrete countertop," and the image that likely comes to mind is of a cold, modern Soho loft inhabited by a nihilist artist or an avant-garde architect. Well, shove that picture right out of your head. "A lot of people associate concrete countertops with a dull, industrial look," says Christian Lincoln, owner of Counter Culture Concrete in Saugerties, New York. "But half of my clients these days are putting them in older houses."
Since just about any pigment can be added to the mix, the possibilities are endless. In addition to limitless color choices, it can be poured into just about any shape, troweled to any texture, and given any edge profile, so it looks at home in a wide variety of spaces. And because each countertop is handcrafted, it has an artisanal quality that other manufactured materials lack.
Growing popularity has assured that you can find pros who make and install concrete countertops nearly anywhere. Expect to pay $75 to $150 per square foot, about on par with granite. See how Lincoln transformed the counters of one New Jersey homeowner...
Many concrete countertop companies offer thousands of custom color options. The color comes from powder or liquid mortar dyes added to the concrete mix. The earlier the dyes go into the hopper, the more uniform the color.
Lincoln dumps in his pigments anywhere from 5 to 13 minutes into the 18-minute mixing cycle, depending on the desired effect. "Some customers prefer a blotchier look," he says. "It creates more character." The amount of dye is usually between 1 and 10 percent of the amount of portland cement in the mix.
Adding any more will compromise the countertop's strength. As for color trends, Lincoln finds that Easterners are partial to steely grays and snowy whites, while West Coasters opt for funkier reds, blues and vibrant oranges.
The first step is to build a melamine form, based on a template made at the client's house. Later, wet concrete will be poured into the form, which includes a cutout for a sink. While some pros pour countertops on-site, most prefer to do it in the workshop, where they can control the process more closely.
Pigment is weighed before being added to the concrete mixture, which also includes portland cement, fly ash—a by-product of coal plants used as a binder—water, and shale aggregate, which is added for strength. Aggregates can be used for decorative purposes, too. If you want a terrazzo look, for example, the counter surface can be ground down to expose aggregates as varied as red volcanic rock or colorful ground-up glass, depending on the desired effect.
Sand, here being measured out, also strengthens the concrete. "The more variation in the size of the sand particles, the stronger the countertop," says Lincoln.
The ingredients are combined in a mixer and tumbled for about 18 minutes, until the concrete slurry reaches the consistency of oatmeal.
The crew starts filling the form with concrete. The work is done on a vibration table, a platform that floats on shock absorbers. Vibrating the mixture for about five minutes gets rid of air bubbles that form during the mixing and spreading, and is the key to creating solid, crack-resistant countertops. Workers have about half an hour to spread the mixture after it's poured into the form before it begins to set.
The countertop gets its backbone from a steel lath reinforcement sunk just below the midline. Workers then use trowels to pull up water from the mixture and smooth the surface, a process that's done intermittently for up to two hours.
After 28 days of curing, the countertop is demolded. Bumps, and this soft, slightly rounded edge profile, are smoothed out with a palm sander.
While the concrete was curing, the surface was treated with a penetrating sealer; more coats are added until the countertop is completely cured and ready for delivery. Topical sealers are more effective against staining than are penetrating types, but they create a glossier, less natural finish.
On installation day, Lincoln loads the countertop into his truck for the two-hour drive to the house. Like a stone slab, it must be transported on its side to avoid cracking, especially around the sink cutout. And since it weighs about 16 pounds per square foot (about the same as granite), the base cabinets have to be made of at least 3/4-inch plywood to support it.
After the counter is dry fitted, it's secured with construction adhesive and leveled with shims. Seams are filled with an epoxy colored to match the countertop, so joints disappear.
Following installation, the surface gets a wipe with furniture or bowling alley wax for added protection. Because concrete is porous, Lincoln recommends reapplying wax every two or three months.
The color recipe is saved in the shop, in the event of damage or for future kitchen additions. The finished moss-green countertops, with matching backsplash, give the client's three children added real estate for eating and drawing.