Because stencils can be used as masks with a variety of decorative materials such as colored overlay cements, chemical stains, water-based stains, sand blasting, and decorative epoxy coatings, their use has been increasing. Of the many materials used to make stencils, the most popular materials are PVC and Mylar plastic. PVC stencil material is between 4 and 20 mils thick and and usually has a self-stick adhesive on one side. Sometimes contractors purchase just the stenciling material, adhere it to a slab, and then cut patterns in place. But more contractors are purchasing precut stencil patterns, which can have incredible detail.
The other material, Mylar, is used to create stencils without adhesive. It comes with precut patterns, and the outside edges are usually taped to a slab. Mylar can be used repeatedly, but you must be very careful to avoid bleed problems.
Companies such as Modello Designs in San Diego, Brickform in Los Angeles, and LesCoat, in Schwenksville, Penn., publish catalogs of patterns. Melanie Royals, president of Modello Designs, says they collect patterns from a variety of sources. They include original art, historical patterns, architectural replica from buildings and structures, tile patterns, patterns used for making fabric, carvings, carpet designs, wall paper, and patterns from different cultures. LesCoat has an extensive collection of patterns that were once used to decorate painted floors when few people could afford carpets. All three companies will create custom stencils from patterns sent to them for a specific project.However a pattern is selected, it must be sized to fit the intended area. Using computer design software programs, the above companies size the requested pattern to fit the dimensions submitted. The next step usually involves your approval that everything is right. Then computer-driven plotters cut the stencil material. Complicated patterns often have a self-stick paper applied on top to hold patterns together while they are adhered to the concrete. The paper is removed when the stencil is in place.
Adherence to surfaces
Smooth concrete is the best surface for good adherence; a deep broom finish is the worst. It's important to get good adhesion for two reasons: you don't want a pattern to move when you are applying a finish, and you don't want bleed-the movement of decorative materials underneath the stencil edge. There are some things you You can do some things that will help. If you are using stencils for sandblast patterning, seal your work first with a coating type sealer to improve adhesion. If temperatures are cool, you can use a heat gun to soften the stencil material; warming the adhesive makes it stick better, too. It's possible to buy stencils with more adhesive, but removal might be more difficult, too. However you do it, when the stencil is applied, you should work it with a roller to ensure good contact.
Aside from achieving good contact between a stencil and the concrete surface, there are some other things you can do:
Chemical stains. Apply thin applications so that the fluid doesn't run on the surface, or mix them with gels such as Modello Gel-lo before they are applied to help prevent movement.
Water-based stains. Apply them lightly with a sprayer pointed at right angles to the concrete. Apply thin coats so that the fluid doesn't move on the slab. You may also use a Prevall Sprayer, which comes with a small glass jar that attaches to a disposable CO2 canister for an air-brush effect.
Overlay cements. They are normally highly viscous materials, so moderate care during the installation is all that's necessary. It is best to choose an overlayment material with a fine aggregate.
Sandblasting. Direct the blast at a right angle to the slab.
Using a liquid resist is one more option. It is applied as a liquid and adheres well to concrete, even deeply broomed surfaces. And it stands up to the abrasion of sand blasting processes as well as the corrosiveness of chemical staining. It also peels off easily afterwards. Mylar stencils are usually used to achieve the intricate patterns possible with stencils. First place them, and then apply the liquid resist to the open parts of the pattern. Remove the stencil when the liquid resist is hard. The resulting pattern will be a negative of the stencil pattern.
Decorative contractors are using stencils for both horizontal and vertical work. Visit the Artistry Demos at the World of Concrete in January to see what stencils can add to decorative concrete work.