Stamped concrete has become a mainstream treatment for anyone wanting more than “plain gray concrete.” However, there is a lesser-known process in which you use a disposable paper stencil to make an impression in concrete. Stencils come in most of the same patterns as polyurethane stamps, and the finished surface looks similar. Most customers cannot differentiate between stamped and stenciled concrete.
The stencil’s purpose is to mask off the color from the concrete, allowing one to color the “stones” with dry-shake color hardener while leaving the joints between them uncolored. This provides a realistic gray “mortar joint.”
Although newer than stamps, commercially produced concrete stencils have been available since the 1980s. I’ve used both stamps and stencils for about 20 years with great results. In many instances, though, stencils provided me the ability to offer customers more choices, accelerated production, a flatter surface profile, and better slip resistance.
Advantages of stencils
Rapid return on investment. Stencils are single-use items—the entire cost can be built into one project. With more expensive stamp mats, often the investment isn’t recouped until the stamps have been used multiple times. If no other customer chooses that particular stamp pattern again, the contractor is out the price of the stamps. With stencils, a contractor can offer customers more than 40 patterns without taking that risk.
Low shipping costs. A roll of stencil is lightweight and compact, so it can be shipped directly to your door by UPS or FedEx for $30 or less. The cost to ship a set of stamps can add $200 or more to the bill. Plus, the weight usually necessitates that it be shipped on a common carrier that probably won’t deliver to a residence.
Fast installation. Stenciling can be accomplished without workers ever getting out on the slab. In most instances, it can be done from outside the forms using long-handled tools. This allows you to pour and finish much larger areas at a time because the window of finishibility is longer. You can also start stenciling as soon as the concrete is bull floated and edged, eliminating the need to wait until the concrete has set enough to bear a man’s weight. I once walked away from a completed stencil job where I still could have sunk my finger through the concrete and down to the subgrade. I was finished before I would have even begun stamping.
Realistic “mortar joints.” Because of the paper thickness, stenciled joints are recessed about 1/8 inch into the concrete, making a surface more slip-resistant than stamped joints. The natural-looking joints can also make stenciled brick look more realistic. On one of our jobs, a brick mason working next door asked how we laid so many bricks so quickly!
Easy learning curve. With minimal instruction (watching a short video may be enough) nearly any competent finisher can turn out a passable stencil job the first time out. This is advantageous when training new employees, or for contractors just starting out in the decorative concrete business.
How to stencil concrete
The first step is to pour, screed, bull float, and edge gray concrete in the normal manner. If the concrete is not excessively wet with bleed water, workers on opposite sides of the slab can immediately place the paper stencil atop the surface. Next, use a stencil roller to plaster the stencil to the surface—but don’t embed it under the paste—so no color can get under the paper. The moisture in the wet concrete helps stick the stencil down. Place the adjacent row of stencil next to the first row, overlapping by one mortar joint to eliminate double-wide joints between rows. Continue this procedure until the slab is covered with stencil.
As soon as the entire stencil is thoroughly flattened against the surface, apply dry-shake color hardener, allow it time to wet out, and then work it into the surface with a bull float. Apply a second coat of hardener to any areas showing insufficient coverage. When the slab is fully colored, the stencils may be removed. This reveals colored stones bordered by uncolored gray mortar joints.
If you remove the stencil early enough, the joints will exhibit the sandy texture and appearance of real mortar. If the concrete has hardened, however, the joints will be much smoother. Under no circumstances should the stencil be left on overnight, as it will be extremely difficult and tedious to remove.
If more than a simple float finish is desired, enhance the surface with texture rollers or seamless skins and either powdered or liquid release before removing the stencils.
After the concrete has hardened sufficiently, saw contraction joints into the slab to control random cracking. Clean off excess antiquing release agent and let the surface dry thoroughly. Apply clear sealer to protect the concrete and enhance its color.
Steve VandeWater is the manager of The Concrete Store in Fishers, Ind. He is a former Indianapolis area contractor and is the creator of the Indiana Decorative Concrete Network website. E-mail email@example.com; also visit www.indecorativeconcrete.com.