How to Build a Mantelpiece

Cut a piece of 1-by-12-inch lumber to the desired length of your mantelpiece to use as a breastplate for your mantelpiece. The breastplate should be at least several inches wider than the fireplace itself on each side.

Hold the breastplate up above the fireplace with the narrow edge flat against the wall so the top edge is about 60 inches above the floor. This is the standard height for a mantelpiece. Measure the fireplace with a measuring tape to find the exact center and line up the center of the breastplate with the center of the fireplace.

If the wall behind the fireplace is brick, secure the breastplate in place by driving 10-inch masonry screws through the wood into the mortar joints between the bricks in the wall behind. To do this, predrill the holes in the wood then set the screw in the hole and drive it into the wall using a power drill. For other types of walls, use a stud finder to locate the studs and secure the breastplate to the studs using 4-inch wood screws.

Measure the distance from the hearth to the bottom edge of the breastplate and cut two identical pieces of 1-by-4-inch lumber to this measurement. Position one of these boards vertically on either side of the fireplace so the bottom edge is flush with the hearth and the top edge butts up against the underside of the breastplate.

Secure the 1-by-4-inch boards in place using the same procedure of predrilling holes in the boards then driving 10-inch masonry screws through the boards into the mortar joints between the bricks in the wall behind using the power drill. These boards will serve as the sides of your mantelpiece.

Cut a piece of 1-by-6-inch lumber to the width of the mantelpiece to serve as the mantelpiece shelf and lay it horizontally across the top edge of the breastplate. The narrow edge of the shelf should be flush with the wall. Secure the shelf in place by driving nails from a nail gun through the shelf into the breastplate.

Create two shelf supports by cutting a 6-inch square piece of 1-by-6-inch lumber in half to form two triangles. Install the triangles beneath the mantelpiece shelf, butting one flat edge up against the breastplate and the other against the underside of the shelf. Use the nail gun to secure the supports in place at either end of the mantelpiece.

Decorate your mantelpiece by attaching pieces of decorative wooden molding to the breastplate under the shelf and to the two vertical side boards. Select patterns that mesh with the existing decor scheme in your room, if you desire, or make your mantel an accent piece by using extravagant details.

Secure the pieces of molding in place by predrilling holes in it and then driving 3-inch wood screws through the molding into the breastplate and the side boards. Once all of the molding has been attached you may choose to fill the nail and screw holes with wood filler. Allow the filler to dry completely and then sand it down to a smooth surface using fine-grain sandpaper.

Paint or stain your mantelpiece as you desire to match the existing decor scheme in your room. When painting your mantelpiece, start with a layer of interior-grade latex primer and finish with a coat of latex paint. If staining your mantelpiece, apply thin coats of stain using a soft brush and wipe away the excess using a clean cloth.