I have been looking at this question also for my own place. NFPA211 calls for 2 inches of masonry for non-rated stoves if the legs are 6"+ tall. Also have seen refs to R 2 for hearth pad. The USG Micore looks to me like a good solution to get thickness and R value. USG says that Micore160 has R1.27, and M300 is R 1.03. Thus ~R2.00 for the 3/4" M160 stuff. Else several layers of 1/2" Durock at R .26. A good solid 3/4 ply base, quickset, suitable number of Micore and Durock or Hardiebacker layers bonded with quickset with tile surface seems like it might work. I did not forget about checking loads on the floor joists. Just to be safe, planning here to add a couple of concrete deck piers and 2x4 cross beams under the 24" oc floor joists in question. It is an old house. Thanks for the forum. Did not realize that brick and tile were so conductive to heat. Whew. Best from WA State.
