Home Depot--and just about any other lumber yard--sells a
product called HardiPlank. It is fireproof. My favorite surface to
solder on is fire bricks. The K-23 insulation brick
I spent some time trying to find out what these two materials are
made from -- got bogged down! Hardie products' website is gorgeous
but WAY too hard to navigate and read and I never found what it was
made from - though it has silica in it, was all I could fathom. They
warn about inhaling silica dust when cutting.
As for K-23, it may (or may not) be made from elements including
clay with alumina hydroxide, or it may be magnesium based.
So the question, if you're using these at very high heat with your
nose close by breathing in all sorts of fumes given off due to the
inevitable reactions, have you made sure they're not toxic?
My soldering boards from Thunderbird come with health statements and
about their reactivity.
Desert Rose Design Studio