How To Apply Exterior Window Mouldings
Take the measurements needed for the pattern:
Front: Measure the window width, adding approximately four inches on each side to cover the window. Allow for additional width of Styrofoam plus the depth (eight inches).
Sides: Measure out how far from the window the cornice is to hang (eight inches ) plus the length of the cornice to match the front (eight inches).
Make a cardboard pattern for the cornices. Cut it so there are two pieces: one for the front and top and one for both of the sides.
Using the cardboard pattern, mark and cut the front, top and two sides with a utility knife. Score the material half way through, and then hit it using the edge of a flat table. File rough edges with another piece of Styrofoam.
Assemble the cornice by first creating the frame (three pieces that resemble a double-ended "L") using toothpicks or meat skewers. Lay the frame on its side and push picks all the way around.
Place the fourth side on top and press down. Clip off any excess picks that are sticking out, and then reinforce or fill holes using a glue gun.
Apply vinyl spackling over the outside of the frame, being sure to cover the bottom but not the side that will be flush against the wall. Add texture while the spackling is still wet by dabbing it with a rubber stamp or sponge (press down and pull straight up). Let dry overnight.
Brush on terra-cotta color as sparingly or generously as desired and let dry.
For a concrete look, apply spackling as above; add texture and let dry overnight. Apply stucco in long strokes with putty knife. Let dry.
Set the cornice on brackets attached to the wall. Reinforce with glue if desired.