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[Cob] Exterior insulation; was Re: Free Bentonite in Seattle and SWIR clay anaysisLeslie Moyer Unschooler at atlasok.comSun Dec 23 20:30:22 CST 2007
jwellman at jwgeo.com wrote: > > On a different note, what ideas have people considered for > exterior-to-COB insulation? > Jesse, I've proposed rockwool (a.k.a. mineral wool), but I know of no one who has used it and I haven't tried it yet. Rockwool is made of mineral slag (a waste product of the coal-burning power plant industry) and sometimes some added basalt, depending upon the composition of the slag. It is vapor permeable. You can get a high R-value in a fairly thin thickness and my thought is that it could be applied to a cob wall and then plastered over. I can imagine dipping it in slip, covering both sides, and then "sticking" it to the exterior, finishing with a final plaster on the exterior. But that's all speculation--I haven't even seen any actual rockwool yet! There are various forms of it....I'm wondering about a semi-rigid sheet. There is a form that comes in fiberglass-like batts, but breathing particles can be dangerous and I can't imagine a way to adhere the batts (they're too flimsy). I don't know how flexible the sheets are....I've read that they can conform to curves, but I don't know how tight a curve they could handle. Some brands of rockwool contain formaldehyde, but others don't and are completely inert. I've encountered some snobbery about using a manmade material with cob, but it hasn't squelched my interest in it. In many temperate & colder climates (including most of the US) the embodied energy in insulation can very rapidly offset the energy used to heat or cool a building--and will continue to provide benefit over the life of the building. And rockwool is mostly (if not totally) a waste product. Many different things can be added to a wall cavity to increase insulation--basically building a double-wall--but it sounds like so much extra work & time. Volcanic pumice can be added as an additive to cob, but for much of the world (including where I live) this wouldn't be locally available. I've read about rice hulls in cavity insulation, but does anyone know if it can be used as an additive? Rice hulls aren't locally available to most places either, but I think I can find a source within a couple hours from here. --Leslie
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