Concrete Stencils,
Stenciling Existing Concrete

Adding pattern to concrete through the use of stencils was one of the earliest applications of decorative concrete. It is also the subject of some of the newest technology in the decorative field today. There are three distinct methods for adding stenciled designs to existing concrete: sandblasting, topping with an overlayment, and modifying the surface with gelled acid etching. All rely on stencils to mask certain areas and expose others to create a design, but beyond that commonality all three techniques are very different in both application and result.

Sandblasting
Sandblasting is one of the oldest techniques for etching patterns into stone, wood, metal, and, of course, concrete. This technique removes the top surface of the cured concrete that is not masked by the stencil, leaving behind a raised pattern.

Sandblasting is truly a one-of-a-kind technique for high-end decorative concrete. While the designs can be and often are very contemporary, the technique has a traditional, historic, “carved-in-stone” feel about it. Since sandblasting is an elaborate, relatively expensive procedure, sandblasted designs usually cover a fairly small area and are almost always custom projects. “It is a way to get something unique,” says Lee Russell, foreman with Lowell Russell Concrete Inc., in Lakeville, Minn. Designs range from family crests on patios, pool decks, even the bottom of swimming pools, to company logos and graphics.

To get started with sandblasting, you’ll need a sandblasting tank and an air compressor. You’ll also need a lot of safety equipment, Russell says, including an air-fed helmet mask that pumps breathable air, and various sizes of nozzles so you can adjust how much sand comes through.

Typically, the nozzle is directed straight down, shooting sand with pressure sufficient to remove the surface of the concrete. The nozzle must keep moving to avoid creating pits or deeper impressions in one spot. Another approach is “shading” — shooting the sand at an angle to create a more dimensional, asymmetrical look.

Of course, “you end up with sand all over the place,” Russell says. He directs sand to a central spot for collection with a backpack blower and then rinses off what is left. For obvious reasons, this technique is more often used outdoors and not often for rehabbing interior spaces.

The concrete mix and finish have an impact on the appearance of the finished project. “I try to get in on the project from the very get-go,” says Clark Paepke, a contractor and international concrete consultant based in Sandy, Utah. “I enjoy that more because I know the personality of the concrete and how to finish it.”