The original fireplace mantel was very plain, a length of 2X6 with some sash trim nailed around the edges. Do to the fact that the hearth was the same width as the outside of the fireplace it would have been difficult to instal a complete surround and have it look right. To give the mantel a sense of stability I decided to add the two corbels. The replacement mantel is basically two 3/4" boards for the top and three styles of stock molding attached to a 1X6 on each side of the corbels.
When I removed the original mantel I discovered that there was no support behind the sheetrock to fasten the mantel to, instead it was anchored with wooden pegs driven into the holes in the bricks. If this worked for thirty-five years I figured it would work again, rather than having to patch the wall after adding framing behind it.
The replacement mantel is made with two corbels and six different dimensions of material:
2 each of 1x10 laminated pine, one ripped to 8" wide the other to 8 5/8" with one corner rounded over, a 1X6 and three styles of molding.
Note: MDF could be substituted for the laminated pine.
The width of the first board for the top depends on the thickness of the corbels, these were 4" so the board was ripped 4 5/8" wider than the thickness of the fireplace top and 9 1/4" longer than the fireplace top. The first board was fastened to the bricks with screws into the wooden pegs, then the corbels were fastened to the board with screws down through the top. A length of 1X6 was fastened between the corbels with pocket screws.
Two lengths of 1X6 were joined to form pieces to wrap around each corner, the bottom molding was fastened to them and the pocket holes were drilled before they were fastened to the top with screws and to the corbels with pocket screws.
The top board was ripped 5/8" wider and cut 1 1/4" longer than the lower board, one corner was rounded over. It was fastened to the top board with 1 1/4" long screws from the bottom, I also put a couple in the center along the back down from the top and filled the holes. I then applied the molding, filled the nail holes and painted it to match the fireplace bricks.