A fireplace is an important feature of a home and it is often the focal point of a room. Fireplaces come in many shapes, sizes and styles and often with new homes, the fireplace will come with a mantle shelf or no mantle at all. Installing a new mantle is left up to homeowners. Many mantles are sold as kits that require a partial assembly by the purchaser but you may have a mantle or may buy an antique mantle that is the correct size for your fireplace. Installing most of these is fairly simple.
Measure the height and width of your fire box (where you have your fire). This is the actual size of your fireplace. Measure the height and width of your fireplace surround. The surround is the noncombustible material covering the face of the fireplace outside the fire box. Your surround may be part of a large brick wall or it may be 12-inch marble tiles (or other noncombustible material) surrounding the fire box. In most communities the surround will be 6 to 12 inches wide, above and on each side of the fire box. You should also have a noncombustible hearth 12 to 18 inches deep in front of the fire box. Check your local codes for precise surround and hearth sizes for your fire box size.
Position your assembled mantle at the fireplace so that it is centred over the fire box and so that the inside edge of the mantle and side legs cover the outside edge of the fireplace surround material.
Place a level on the mantle to make sure it is level. Trace the outline of the mantle and both legs onto the wall using a pencil. Most mantles are hollow so it will not be heavy but it is also large so lifting with two people is a good idea. The outline of the mantle will be helpful as a guide as you install the mantle.
Lay the mantle face down on the floor. Measure for one cleat to run the hollow width of the mantle. You are using 2-by-4-inch boards for the cleats so cut your cleats so they fit inside the hollow top portion of the mantle. The 4-inch side of your 2-by-4-inch board will mount flush to the wall. Measure how the board fits inside the mantle. Transfer that measurement to the wall using your mantle outline as a guide. Example: If the cleat is positioned 12 inches from the outside edge of the mantle and 1/2 inch below the top edge then you can mark 12 inches from the outside edge of your wall drawing and 1/2 inch below the top line. This shows you where to install the cleat so that the mantle will fit. Each side pillar of the mantle should also be hollow. Cut a cleat to fit inside each pillar and mark the location of each cleat on the wall.
Drill a 1/2-inch deep pilot hole through the top cleat. If you are screwing into brick line the hole up so that it goes into the brick and not the mortar as brick is stronger. Use a 2 and 1/2-inch concrete screw. Attach one screw every 12 inches along the cleat. If you are screwing into drywall or studs use a 3-inch decking screw. Screw all three cleats to the wall.
Assemble the mantle and legs together. Slide the mantle over the cleats so that the mantle matches its outline on the wall. It should fit perfectly. With the mantle snug to the wall, screw through the top of the mantle into the cleat using a wood screw with a recessed head. Space your screws every 16 inches. Screw through the side of the mantle legs and recess your screws.
Position trim moulding along the inside edge of the mantle legs and along the bottom of the mantle top. Use 4d finish nails every 12 to 16 inches. Most mantle kits provide this moulding already cut or you can cut your own. Fill your nail holes and screw heads with wood filler. Allow the fill to dry and sand the areas flush. Caulk around the perimeter both outside and inside to fill any seams and gaps using a paintable caulk.
Prime and paint your new mantle to match the trim in your house for a cohesive look.