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Secrets of Better Concrete Stenciling
by Gail Elber
Stencils aren't only for use on new concrete; they can be used with overlays, which consist of cementitious material mixed with a polymer component so that it spreads thinly and adheres to the underlying concrete. Not all overlays can be colored or stenciled; so, make sure you use a product advertised as a "stampable overlay." These products won't run under your stencil or stick to it prematurely. They can be integrally colored, then treated with acid stain or colored with color hardener or iron oxide pigments to create natural-looking effects.
 Overlays can be troweled on, or sprayed on with a hopper or spray texturing system. Benron Equipment and Supply offers the most advanced system currently available for delivering total operator control and flexibility in achieving the most desired textured finishes. If you trowel, use adhesive-backed stencils that won't be dislodged by the trowel.
Prepare the slab according to the overlay manufacturer's directions. In addition to repairing cracks, you must thoroughly wash and degrease it. Some overlay manufacturers offer a primer that improves the adhesion of their product to the slab. When the slab is ready, apply the stencils, and then spray on a 1/8-inch to 1/4-inch layer of overlay material. You can walk in the wet overlay wearing golf spikes, whose marks will be erased when you knock down the overlay with a trowel. Overlays can also be textured with mats or rollers, and then sealed as concrete is.
If you want the grout lines of your faux masonry to be some color other than that of the underlying concrete, you'll have to apply two overlays -- one applied over the whole surface to provide the grout color; then another layer over the stencils in the desired color of the stones or tiles.
Walls, also, can be stenciled with an overlay product. Use adhesive stencils, and trowel or spray on your overlay just as on a floor.
If you find yourself doing a lot of the same overlay patterns and designs, high density plastic stencils are worth considering. "You get the same results [as with paper stencils]," observes Ken McKinnon, vice president of operations at Seamco Laboratories Inc., the Tampa, Florida-based company that introduced neoprene stencils. "The big advantage is that our stencils are reusable -- indefinitely."
Because they are a little thicker than paper stencils, they produce more pronounced grout lines and they lay down flat without glue -- eliminating the glue-down step associated with paper stencils. The down-side to plastic stencils, reports McKinnon, is that they are difficult to trowel over. They also have inherent problems if you're working on a vertical surface; they don't stick on their own. But, on the up-side, because there's no glue involved, plastic stencils are easily repositioned on horizontal surfaces and they don't leave a glue residue.
Uneven surfaces shouldn't present a problem since, in most overlay situations, you would apply a scratch coat in the grout color, which will smooth the surface. And don't worry about what happens to plastic when it gets cold -- you shouldn't be applying acrylic or cementitious overlays when the temperature falls below 45 to 50 degrees.
Another plus is that the plastic stencils just peel off and cleaning them is a cinch. McKinnon explains, "After the cement material dries, just hit them together and the cement pops right off."
In addition to creating faux masonry surfaces, you can use stencils to apply color to concrete and create logos, signs or decorative designs, but forget liquid acid or acrylic stains with stencils because the stain creeps under the edges of the stencil. Adhesive stencils allow you to use brush-on gel-type acid stains. The accompanying photo feature shows another technique: using stencils for gel-type acid etching.
Adhesive stencils intended for sandblasting offer other options, but that subject is worthy of an article in itself, so we won't cover it here.
Stencils offer a few advantages over stamps. "With stencils, you can cover two-thirds more area in a day with the same crew compared with stamps," says Piccolo. "You can get on the concrete sooner with your texture and color, right after you bull-float it, where with stamped concrete you've got to wait till the concrete gets to a certain set phase before you can get on it with your tools."
Merrick Pierce of Specialty Concrete Services in Natchitoches, Louisiana, has worked with both stencils and stamps, and says that the choice a matter of personal preference. "The way I see it, with the stamps, the patterns like slate and the stone patterns look really good, but the brick patterns look better with stencils because they look like they have a real mortar joint." You can combine stamps and stencils on a job if you need a realistic "stone" patio surrounded by a realistic "tile" border. And if neither you nor your rental shop owns the particular stamp that a job calls for, stencils can fill the bill.
Perhaps the biggest advantage of stencils over stamps is that you can order custom stencils. Stencil manufacturers will cut custom stencils for you to create a particular pattern, logo or artwork.
Neither method offers a big price advantage over the other. In a given region, stenciling and stamping cost the client about the same.
If stenciling interests you, attend one of the workshops offered by the makers and distributors of stencils and overlay compounds. Look for training opportunities by visiting Concrete Decor's Events and Training Page and checking the "Calendar of Events." With training and some practice on your own, you'll soon be ready to add this versatile technique to your repertoire.
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