How to Build a Large Mantel for a Fireplace

Installing the Mantel Support

• 1

  Measure the width of the fireplace with a measuring tape. Add 20 to 30 inches to this measurement to determine the length of the fireplace mantel. The more inches you add, the larger your mantel will be.

• 2

  Cut a piece of 2-by-4-inch hardwood using a circular saw to the determined length. This board will serve as the support for your fireplace mantel. You will construct the mantel frame out of hardwood and attach it to the piece of 2-by-4-inch hardwood.

• 3

  Hold the piece of 2-by-4-inch hardwood horizontally up against the wall above the fireplace. Adjust the board so its widest edge is flat against the wall and its bottom edge is at least 60 inches off the ground. This is the standard height at which fireplace mantels are typically installed.

• 4

  Mark the top and bottom edges of the 2-by-4-inch piece of hardwood in pencil every 6 inches. If the wall behind your fireplace is brick, adjust the spacing of these marks so they are aligned with the mortar joints between bricks. For drywall, use a stud finder to locate the wall studs and align your marks with the studs.

• 5

  Remove the hardwood board from the wall and predrill holes through it where you made the pencil marks using a power drill. When finished, place the board back in the position from which you removed it.

• 6

  Drive 6-inch masonry screws through the holes in the 2-by-4-inch hardwood board into the mortar joints between the bricks in the wall above the fireplace. If the wall is drywall rather than brick, use 6-inch wood screws instead.

Constructing and Install the Mantel Frame

• 7

  Cut two pieces of 1/2-by-8-inch hardwood to the same length as the mantel support using a circular saw. These pieces will serve as the top and bottom panels of your mantel frame. Cut a piece of 1/2-by-5-inch hardwood to the length of the mantel to serve as the front panel.

• 8

  Use the circular saw to cut the two side panels for your mantel frame out of 1/2-by-8-inch plywood. These pieces should both be 8 inches wide and 5 inches tall.

• 9

  Stand the top, bottom and side panels upright on their longest narrow edges. Arrange these four boards in a rectangle shape, placing the two side panels flat against the ends of the top and bottom panels. Align the edges of all four panels.

• 10

  Drive nails from a nail gun through the side panels into the thickness of the top and bottom panels to secure the mantel frame. Lay the front panel flat across one of the open sides of the frame and align the edges. Attach the front panel by driving nails through it into the four sides of the frame.

• 11

  Fit the completed mantel frame over the piece of 2-by-4-inch hardwood you attached to the wall above the fireplace earlier. The 2-by-4-inch board should fit snugly inside the mantel frame. Adjust the form so its back edges are flush with the wall.

• 12

  Drive 1 1/2-inch wood screws through the mantel frame into all four sides of the hardwood board to secure it in place. Countersink the screws slightly below the surface of the mantel frame.

• 13

  Fill all nail and screw holes with wood filler. Spread the wood filler with a putty knife and allow it to dry completely. Once the filler hardens, sand the surface of the mantel form smooth using fine-grain sandpaper.

• 14

  Paint or stain your completed fireplace mantel to match the existing decor in your room.