[Cob] Exterior insulation; was Re: Free Bentonite in Seattle and SWIR clay anaysis

[Leslie Moyer]

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