I'm sorry CJKarl, can you explain a little more? I thought the weight of the bricks above where you cut for the mantel might have been an issue. The reason I ask is because the owner of a building I just bricked wants to know if I can remove some brick in the middle of the wall, and replace it with a " P " made of brick. The area would be about 6' x 6'. It has the weight of maybe 10' of brick above it.It was built with type N and it's just a veneer.
I don't see a problem with the weight. It appears to be about 12-14 inches of stone. Approximately 4 inches will be supported completely and the corble will extend the support out an additional 5-6 inches in three spots. almost half the stone will be setting on brick.
The brick above should easily be heavy enough to "hold down" the new mantle. By properly cleaning out the opening,as the picture shows, the new stone will seat evenly and deeply into the shelf. A little extra time with a margin trowel to ensure the bed joints are completely filled and put a support stick to allow the mortar to set up will finish this remodel quite nicely.
I say it is all about compressive strength which is where masonry is the strongest.
I am now creating a new account to create a dead end for the ensuing criminal investigation that is sure to follow the unfotunate collapse of the insanely heavy mantle.:w00t:
Once again nicely done.