How to Assemble a Wood Frame for a Wall Mirror

Rout one edge on the back side of each trim board, using a router table equipped with a 3/8-inch straight bit. Rout the edge to the depth of the wall-mounted mirror.

Cut a 45-degree angle on each end of each trim board, using a miter saw. One side of each board should still measure 24 and 48 inches respectively. The angles will be opposing each other. Each cut should point inward toward the routed edge. The long edge is the outside of the board and the short edge is the inside. They will fit together to form a picture frame-style rectangular box.

Place the trim boards together to form the rectangular box. The routed edges of the box will be on the inside edge on the back side of the trim.

Fit each board around the mirror on the wall. Hammer finish nails through the trim boards into the wall every 4 to 6 inches to fasten the frame around the wall-mounted mirror.

Set the nails approximately 1/16 inch deep into the surface of the trim boards by tapping the head of the nail set with a hammer when the point is resting over the finish nail head.

Fill the nail holes with wood putty, using a putty knife. Allow the putty to dry for 24 hours.

Sand the putty flush with the trim boards and continue to sand the entire frame until it is smooth, using fine-grit sandpaper.

Apply a wood finish to the frame, using a paintbrush. Allow the finish to dry for 72 hours.