I have a 75cm deep x 1m wide space in which I will fit a woodburning
stove. I want to line the raw stone walls of the old fireplace space
with a well insulating and obviously heatpoof material so that the
woodburner does not lose heat into the walls.
What lining material do I use for this task?
Mortar with a high lime proportion is supposed to be heatproof. As
mentioned, loading it with vermiculite may work. Certainly that is used
behind fireback inserts I believe.
Presumably you can't use line the space with rockwool as the stove won't fit
the space exactly? I have an inset firebox, and that sits in an opening
lined with rockwool, but you can't see it because the firebox completely
blocks the opening.
High alumina cement with pearlite makes an insulator that will
withstand 700C, I heard of a chap making chimanea with it. You need to
check part J for correct stand off distances. This also allows enough
air circulation round the heat exchange surfaces.
I don't know what the k value of this would be but before the scale of
the job daunted me I was considering hacking off the plaster of our
solid exterior walls and using a pearlite cement mix rather than dry
lining, I'm still cogitating.
Ah, this is in my bailiwick - I'm a geologist.
Gypsum as such contains 2 molecules of water to each molecule of
calcium sulphate. It will dehydrate to one half-molecule of water per
sulphate at about 140C, at which point it becomes the active ingredient
of "Plaster of Paris" ; heating further to ~180C and you'll drive off
the remaining water to form anhydrite. There's a significant volume
change too - anhydrite is denser than gypsum. At very high temperatures
anhydrite will lose SO2 to form calcium oxide. As this mix cools, it'll
pick up water and CO2 from the air, forming a more cement-like mixture.
The volume changes on dehydrating gypsum to anhydrite will cause
some damage to the structure of whatever you heat up that much, but the
endothermic (heat-absorbing) nature of the reactions will slow down the
reaction a good deal, and the porous nature of the materials will
substantially reduce the penetration of heat into the structure (which
is why drywall is an effective fire retardant.). But because of the
volume changes, I wouldn't go around treating my plasterboard like
that. Now, where'd I put those bits of broken up asbestos board from
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