I believe concrete is .095 per inch, not .95. It has to be pretty thick to protect. That is why no combustible underneath.So concrete is in contact with combustibles on the bottom side. I guess that doesn’t concern me as much if its just the hearth. concrete has an R of 0.95 per inch
Sweep's Library - R Value of Hearth Materials
My wood stove requires floor protection with a certain R value. Where do I find this rating?
hearth.com