Step 1 - Mark the center of the firebox and the wall.
Step 2 - Measure the width of the hearth and mark the center. Dry fit and mark for placement. Apply construction adhesive to the back of the hearth. Set the hearth stone in place and align the center marks.
Step 3 - Locate the riser piece (if using) and dry fit it on top of the hearth. It may need to be cut to the proper size to cover the space between the hearth and the underside of the firebox if you did not order a custom sized mantel.
Step 4 - Cut one 2x4 wood stud into six pieces, each piece should be no longer than 6" long.
Step 5 - Use construction adhesive to secure one piece of wood into the back of the fireplace leg, near the top of the leg. (see diagram)
Step 6 - Measure the underside of the mantel shelf to determine the width from outside leg to outside leg. Center this dimension on the firebox and mark each side as a guide for the outside of each leg.
Step 7 - Measure to the top of the piece of wood you secured to the back of the mantel leg. Measure from the top of the hearth vertically up the wall on each side and mark 1.5" away from the line marking the outside of the mantel leg. Take two of the smaller wood lengths you cut earlier and screw them into the wall, securing firmly. These pieces will need to match up with the pieces at the back of the mantel leg.
Step 8 - Dry fit the two facing legs on the inside of each installed mantel leg to assure a good fit. Remove, apply construction adhesive to the back of each leg and secure to the wall.
Step 9 - Dry fit the facing header on top of each installed facing leg to assure a good fit. Remove, apply construction adhesive to the back of the header and secure to the wall.
Step 10 - Take two pieces of the wood you cut earlier and secure each to connect the wood blocks on the back of the mantel leg and the wall. (see diagram)
Step 11 - Locate the mantel breast plate and dry fit to confirm fit. Apply construction adhesive to the top edge of the mantel leg and secure it.
Step 12 - Dry fit mantel shelf on top of mantel breast plate. Apply construction adhesive to the top of the breast plate and set mantel shelf on top.