This page demonstrates a newer, better way to install floating mantels and shelves. No more working with Re-Bar and wood adhesives. We found these newer products at a place called Sheppards Brackets , you can also find them on Facebook. They sell the mounting brackets and tools for installing them.
Some of the highlights can be found here on these pages:
Calculating How Much Your Sheppard Bracket Can Hold
What bracket should I choose?
Extra Long Shelves
Sheppard Customer Projects