Stenciling is used in decorative concrete to add patterning effects that are too complex or detailed to be reproduced on concrete through the scoring of lines. Decorative concrete stenciling can be done in a variety of ways. First, a thin cement overlay may be sprayed or troweled over a stencil, and the stencil removed once the overlay has hardened. This is the method used in the photo at left. It is best for repeating patterns like brick, cobblestone, and slate, and it may be used over an entire area or just as a border. You can see some of the patterns available for stenciled concrete overlays from: Artcrete Concrete Stencils.
Stenciling may also be done by etching a pattern into concrete or a cement overlay using plain or colored, gelled muriatic acid. This method is best for intricate patterns that require great attention to detail, such as stylish borders and complex custom images. These patterns become a permanent part of the concrete and usually go no deeper than 1/32". You can see samples and read more about this process at: Modello Designs and Surface Gel Tek. Finally, concrete stenciling can also be accomplished through the engraving process (as described above), or through sandblasting, where a greater physical depth is desired than can be achieved through concrete etching. Here is an example of a Stencil Engraved in Concrete.