I'm thinking about building my own hearth extension for my Revere insert. I've searched the forums and read most of the posts about hearth extensions, as well as the Wiki article on Hearth Design. I also checked my manual for hearth requirements, and all it says is that it must extend 16" (I understand now 18") beyond insert and be non-combustible and at least .018" thick (26 gauge). Does this mean I don't need to worry about R-values and that the hearth is mainly for spark (log roll-out) protection? If so, can I just use plywood topped with ceramic tile? Or can you not put tile directly on plywood and need a cement board as a basic foundation (not for insulation purposes). Sorry to sound like a newb, but when it comes to tile I am. Any suggestions on the easiest way to go about this would be great. Looking to make my extension about 18" x 48". Nothing fancy - just want to stop having to use my 2 giant pieces of slate. I'd like to trim it with some nice wood trim, so my thickness needs to work out with this in mind. Thanks!