Hi Mel,
I see.
I think you want granite for the oven landing (in front of the oven, where you set food going in and out), which works really well, but not under the oven. You will want a traditional insulating hearth, with two layers -- a concrete thermal layer and a vermiculite concrete insulating layer. The thermal layer absorbs and returns heat to the oven chamber, and the vermiculite layer stops the heat from leaving.
The good news is that the hearth is neither expensive or difficult to build.
Does this help?
James |