How to Install Exterior Window Molding
- 1). Measure the top of the window opening, along the inner edge of the casing, from corner to corner, using a tape measure. Mark out the measurement on a piece of exterior trim molding with a pencil, with two marks and half a foot or more past each of them.
- 2). Lay the trim face-up on a miter saw, with the bottom edge toward the blade and one mark under it. Turn the blade 45 degrees outward from the mark. Make the cut.
- 3). Reposition the trim so the second mark is under the blade. Turn the blade 45 degrees in the other direction. Make the cut.
- 4). Hold the trim along the top edge of the window opening, with the two ends angling upward off the two top corners. Secure the trim with your finishing nail gun, putting pairs of nails every 10 or 12 inches along the length.
- 5). Repeat the process for the other three sides of the window opening. Butt the mitered ends tightly to each other to form the corners.
- 6). Run unbroken beads of caulk around the trim, where it meets the wall and the window. Let the caulk set for 24 hours before you paint the trim.