Brick and Drywall
The back of your beam should be notched out to fit on a 2 by 4.
Locate on your wall, where you want your mantel to rest and mount a 2 by 4 on the wall. The entire weight of the beam will be on the 2 by 4, so be sure that it is well secured.
Place your mantel on the 2 by 4 and screw from the top of your mantel down into the 2 by 4. We suggest using 3 to 4 screws from the top and 2 screws from the bottom up.
For brick or any masonry use mason screws plus construction glue to mount the 2 by 4 on the wall
Stonework
If you are mounting a mantel where there will be stonework laid later, we recommend that you use steel straps on your mantel. These straps are predrilled with holes every 2 inches.
The steel straps are screwed to the back of the beam, with one hole extending below the mantel and 2 to 3 holes extending above the mantel. We suggest that you use one strap per 25 pounds (ie: 4 straps for a 100 pound mantel).
Locate the wood framing on the wall and attach straps using 3 to 3 1/2 inch screws.
Hint: To keep from burying your mantel in the stone, you can build out the back of your mantel by adding a 2 by 8 board to it. Then you would attach the straps to the 2 by 8 and mount as described above. This allows more of the beam to protrude above your fireplace. The stonework then goes around the mounted mantel.