Brick molding, or brick mold, is used on exterior door and window frames to bridge the gap between the door or window jamb and the wall's brick or siding. Its purpose is similar to interior door and window casings. The outside edge of the brick mold is thick and square to provide a substantial base or anchor for the exterior wall finish material. PVC brick mold is a plastic composite material that is water-, insect- and rot-resistant, making it a durable choice for exterior appliactions. Use it to replace wood brick molding or start from scratch using PVC brick mold. It cuts just like wood.
Measure around the inside perimeter of the window frame and add 1/4 inch to each measurement. If you're measuring for a door, measure across the top and the two vertical sides. The extra 1/4-inch is to provide a reveal or lip between the edge of the brick molding and the window or door frame.
Set the blade of a miter saw at 45 degrees. Place the molding flat on the miter saw table facing up. The back, square edge that butts against the brick should be facing you.
Hold the molding tight against the fence with one hand. Use the other hand to trim 1/2 inch of the molding off at 45 degrees.
Measure from the short point of the miter cut that you just made, and make a mark on the thin (inside) edge of the molding. Swing the miter saw blade to the other side and cut the molding at the mark, making a 45-degree miter that opposes the first miter cut. Repeat the process for all four pieces if you're doing a window.
Repeat Steps 2, 3 and 4 to miter-cut the top ends of the side molding pieces for a door. Measure from the short point of the miter on each piece, then square-cut the bottom end at 90 degrees.
Fit the pieces on the window or door and check the fit. Trim as needed until all the miters fit tight.