Thank you for your question.

I wasn't there when Junior Briggs installed this shelf and corbels, but I believe they are simply mortared into the veneer wall.

The angled corbels do most of the work, transferring the weight of the shelf to the wall. The 2" +/- thick Country Ledgestone has enough depth to bed everything securely.

If we do anything heavier, or cantilever it (no brackets or corbels), then we have to do something a little more serious about anchoring the shelf securely. We have to assume that at some point someone will be stand on top of the shelf to hang a picture or decorations, and no one wants a 400 lb. shelf to come off the wall.

The stone shelf below has all-thread studs epoxied into the back that extend through the frame wall, with lock nuts and washers to keep it in place.

In either case, the shelf needs to be installed first and the veneer installed afterwards.

Beautiful work! In the picture above where you describe the installation of the mantel, what is the stone?

The photo directly above is Southern Ledgestone from Cultured Stone (Boral). I'm not sure about the color. The hearth and shelf are natural Tennessee Crab Orchard stone.