How to Build a Floating Fireplace Mantel

Measure the width of your fireplace using a measuring tape. Add at least 12 inches to this measurement to determine the length of your floating mantel. By adding 12 inches to the measurement your mantel will extend beyond the fireplace by about six inches on either side.

Use a circular saw to cut a piece of 1-by-2-inch hardwood to the length measurement you determined earlier. This piece of wood serves as the breastplate for your floating mantel. The mantel form is attached to the breastplate to secure the finished mantel to the wall.

Hold the breastplate up against the wall at the desired height above the fireplace. Position the breastplate so its 3-inch side is flush with the wall and its bottom edge is at least 60 inches off the floor. This is the standard height for a fireplace mantel.

Make pencil marks approximately every eight inches along the entire length of the breastplate. Align your pencil marks with the mortar joints between the bricks, if your fireplace is installed in a brick wall. If the wall is drywall, use a stud finder to locate the studs and align your pencil marks accordingly.

Predrill holes through the breastplate where you made the pencil marks. Hold the 1-by-2-inch board flat against the wall in the same position as before and drive 3-inch masonry screws through the predrilled holes into the mortar joints between the bricks. If you are installing your mantel in drywall, drive 3-inch wood screws through the board into the wall studs.

Cut three pieces of 1-by-6-inch hardwood to the length of your breastplate using a circular saw. These boards serve as the top and bottom for your mantel form. Cut two more pieces of 1-by-6-inch hardwood to a length of 4 inches. These pieces serve as the ends of your mantel form.

Stand the four boards you just cut upright on their longest narrow edges. Position the two longer boards parallel to each other and lay the shorter boards perpendicularly across the ends to form a rectangular frame.

Adjust the boards to align the edges; the ends of the shorter boards should be even with the outside edges of the top and bottom boards. Using a nail gun, drive nails through the outside of the shorter boards into the thickness of the top and bottom boards to secure the frame.

Cut a piece of 1-by-4-inch hardwood to the length of your breastplate, plus two inches. Lay this board flat on top of one open end of the frame you just constructed, aligning the edges. Drive nails through the front of the 1-by-4-inch hardwood board into the frame beyond.

Fit the mantel form you just completed over the breastplate you attached to the wall earlier. The open side of the mantel form should fit snugly over the 1-by-2-inch hardwood breastplate. Secure the mantel frame by driving 2-inch wood screws through the top, bottom and sides of the form into the breastplate.

Fill all screw and nail holes with wood filler and allow the filler to dry completely. Sand the surface of the wood smooth using fine-grain sandpaper.

Paint or stain your floating mantel to match the decor scheme in your room. Once the finish has dried, you may choose to apply a coat of clear varnish or polyurethane in a matte or glossy finish.