How to Make a Mantel Shelf

Cut four pieces of 1/2-inch-thick plywood, 4 inches wide and the length of the mantel piece. Cut two 4-by-4-inch squares. These pieces will serve as the mantel shelf box.

Cut six pieces of 1-by-2 lumber the length of the mantel piece. Cut four 3-inch-long pieces of 1-by-2 lumber. These pieces will serve as braces inside the mantel box.

Apply wood glue to the back of a plywood piece and stick it above the fireplace. This is the back of the mantel box. Put wood glue on two of the 1-by-2 strips and align them with the outer inside edges of the plywood. Attach a 4-inch-long strip at the end. Sink finishing nails evenly spaced along both strips.

Attach two more lengthwise strips directly on top of the first using wood glue and finishing nails. This will give you a 2-inch-wide ledge on the upper and lower portion of the mantel box piece.

Lay a piece of plywood on a flat work surface and assemble the front of the mantel box exactly as the back. Make sure every piece is properly aligned. You will attach only two strips during assembly of the front mantel box piece.

Apply wood glue along the top edge of the mantel box front. Place the third piece of plywood on edge and seat it in the glue to make the first 90-degree joint. Repeat this step for the bottom edge. Glue one four inch long strip at each end. Allow the glue to dry and sink finishing nails along the edges to produce a sturdy joint. A three-sided box is the result at this point.

Apply wood glue to the top and bottom edges of the mounted mantel box backing. Turn the hollow mantel box on edge with the front facing out. Attach it to the mantle box backing with the edges butting up to the wall. Sink screws along the top and bottom edge. Close the ends of the mantel box with the 4-by-4-inch squares.

Cut a 45-degree right-hand angle at each end of 6-inch-wide crown molding. Glue the crown molding to the front of the mantel box. Tap in 6d finishing nails along the top and bottom every six inches. Cut two 6-inch-wide crown molding pieces at a 45-degree left-hand angle, creating an outside joint. Glue and finish the assembly with 6d finishing nails.