How to Install a Heavy Slab Floating Mantel

Hold the mantel above the fireplace at the height you wish to mount it, at least 6 inches away from the firebox. Place a level on the mantel and adjust the mantel so it sits straight. Ask a friend to trace along the top of the mantel, then set the mantel aside.

Turn the mantel face down and measure the distance from the mantel's top edge to the gap in the mantel's backside. Measure this distance down from the line you just drew, in two locations. Use a level as a straight edge and connect the two marks with a line. If you are mounting the mantel on drywall, run a stud finder along the second line to locate the studs.

Line up the supplied mounting bracket's top edge with the second line. If your mantel did not come with a mounting bracket, measure the gap's length along the back of the mantel. Transfer this measurement to a 1-by-2-inch board and cut it with a handsaw.

Drill five pilot holes through the mounting bracket and into the wall. If the wall is brick or stone, use a hammer drill and a masonry bit the same size diameter as the masonry lag bolts you will use. If the wall is drywall, position at least two pilot holes over wall studs using a 1/8-inch drill bit. Drill the remaining pilot holes with a drill bit the same diameter as the wall anchors you will use.

Secure the mounting bracket to the wall. For stone or brick walls, insert the lag bolts' sleeves into the pilot holes, then drive the lag bolts into the sleeves with a lag screwdriver. For drywall, use a hammer to tap a wall anchor into each pilot hole not entering a wall stud. Drive 2-inch screws through each pilot hole to hold the mantel in place.

Fit the mantel over the mounting bracket. Drive finishing nails through the the top of the mantel and into the mounting bracket with a pneumatic nail gun. Space the nails 6 to 8 inches apart.