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?
Browning contains a high %age vermiculite, that is what I'll be using. That'll give some insulation, the thicker the better.
'Browning' ?
I am unfamiliar with that term. Is that a panel of some kind?
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.
Andy.
Surely you've heard of the famous detective, Carlite Browning?
Really it's a type of base coat plaster which is pinky brown in colour.
Yup. It will go crumbly with a blowlamp, but its pretty good up to that.
Thanks Andy, I could, the space is big enough. If I was to use rockwool is there a safer equivalent of asbestos sheet with which to sandwich the wool against the building walls?
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.
AJH
Browning contains perlite. Bonding coat contains vermiculite. Gypsum based plaster is unsuitable so I'd say buy some vemiculite and mix it with sand and cement and render that on.
I've had gypsum plaster glowing red hot when soldering pipes with a blow lamp. Doesn't seem to do any harm other than discolouration.
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 the cellar?
The better material is masterboard/multiboard, which is reckoned to take a bit more heat.
Its IIRC glass strands and a better sort of cement..but don't ask me which one.
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