Brick mold is typically profiled on the front for aesthetics, meaning it has differing levels on the face. The profile is typically a gentle roll or curve -- just enough to differentiate it from a rectangular piece of trim. The back or side of brick mold may or may not have a profiled slot, channel or rabbet, for the purpose of fitting over the edge of other materials, such as siding or sheathing.
Brick mold is typically manufactured using softwood such as Douglas fir, hemlock or spruce but may also be purchased in weather-resistant cedar, redwood or any other wood species commonly used for exterior molding. PVC or vinyl brick mold is available as well -- it is typically stark white but also comes in other colors. Wood brick mold is often sold primed with off-white sealant.
Thick as a Brick
Most trim and molding is 3/4-inch-thick, but brick mold, at 1 1/4 inches thick, is almost twice as thick as standard moldings, specifically to butt up against bricks, which are typically 1 1/2 inches thick or thicker. The thicker profile of brick mold often complements construction materials better than thinner moldings.
There isn't always enough room to accommodate brick mold when replacing older trim on siding. In this instance, the carpenter snaps lines vertically and horizontally around the door or window, cuts and removes a strip of siding and or sheathing and places the brick mold in the recess. The extra thickness of brick mold allows the siding to butt against it on the outside and provides a reveal or lip on the inside.
Glue and Nail
You can usually install brick mold with 3-inch nails. Nails should penetrate through the brick mold and into the framing behind it by at least 1 inch. Use wood glue on mitered corners for standard wood brick mold. Use an appropriate glue for corners on PVC or other synthetic brick mold.