Use a biscuit joiner to make 45 degree slots along one long, beveled, ¾-inch edge of a ¾-by-6-1/8-inches pilaster. The height of the pilaster depends on the height you want the fireplace cabinet.
Space the slots 6 inches on center. Repeat this process on three more pilasters.
Place plate-joining biscuits into the slots that you just cut from two of the pilasters. Use wood glue to help secure the biscuits into the slots.
Align the edge of the pilaster that has the biscuits in it with the beveled edge of a pilaster whose slots are bare. Join the two pilasters together by sliding the exposed biscuits on one pilaster into the open slots on the second plaster.
Secure the biscuits and pilasters together with wood glue. Repeat this process with the remaining two pilasters.
The joined pilasters form the legs of the cabinet.
Cut a 3/4-inch-thick birch plywood board according to the height and length that you want the face of the mantle, not counting the space that the surround takes up. This board is the frieze board.
Secure the pilasters that you joined to the shorter sides of plywood using a nail gun. The top of the plywood board and pilasters should be flush because this is the edge where the mantelshelf will sit.
Dry-fit the fireplace cabinet onto the wall where you want to install it. Use a pencil to mark the inside edges of the pilasters that form the sides of the legs onto the wall.
Cut a ¾-inch-thick mantelshelf according to the depth and length of your choice.
Secure the mantelshelf to the top edge of the cabinet legs and the sheet of plywood between them with a bead of wood glue. Reinforce the pieces with a nail gun.
Drive the nails from the top of the mantelshelf into the pilasters and plywood.
Cut two 1-by-4 lengths of lumber that are the same height as the cabinet legs. These pieces of lumber will serve as the backings for the legs.
Install the backings vertically against the wall where you are going to place the cabinet. The outside edges of the backings should line up with pencil marks you made on the wall.
Secure the backing for the legs to the walls with nails spaced 6 inches apart. Use anchors and screws instead of nails, if necessary.
Measure the distance between the two backings for the legs and cut another piece of 1-by-4 lumber according to that measurement.
Install the length of lumber that you just cut horizontally between the two backings for the legs.
Slide the fireplace cabinet over the backing pieces that you installed onto the wall. Use a nail gun to secure the cabinet legs and mantelshelf to the backing.
Space the nails by 6 inches.
Install 7/16-by-3¼-inch dentil crown molding under the mantelshelf. Use nails spaced 10 inches apart to secure the molding to the pilasters and the face of the cabinet.
Install ¾-by-1½-inch beaded trim around the opening of the fireplace cabinet. Secure the trim to the cabinet legs and face with nails spaced 10 inches apart.
Fill the nail holes with wood filler.
Things You Will Need
- 4 pilasters measuring ¾-by-6-1/8-inch
- Tape measure
- Biscuit joiner
- Plate-joining biscuits
- Wood glue
- Nail gun
- ¾-inch plywood
- ¾-inch thick mantelshelf
- 1-by-4 lumber
- 7/16-by-3¼-inch dentil crown molding
- ¾-by-1 ½-inch beaded trim
- Wood filler
- Stain or paint the fireplace cabinet in the color of your choice.
- Use half-round bands and other types of trim or molding that you like if you want additional decorative items on the cabinet.