Cob: RE: Insulation - vermiculite

[Sojourner]

"Kelly, Sean" wrote:
> 
> Grace and Holly,
> 
> thanks for the info (you learn something new everyday!)  That
> stuff is like some sort of air popped rock, right (not really
> styrofoam)?

That's perlite.  I don't know WHAT its made of.

Vermiculite is heat treated mica.  It "explodes" into little crumbly
accordian-pleated bits.  As someone has reminded me, vermiculite soaks
up something like 3 times its weight in water, so it would be a Very Bad
Idea to add it to a cob slurry, I would imagine.

In fact, given its propensity for acting like a sponge, I'm not sure it
would be all that good an idea to try to use it even as cavity fill. 
You'd have to be extra certain-sure to protect it from moisture
encroachment.

However, perlite, the white styrofoam-like stuff, is just about
waterproof.  You could use it as a cob additive, but you would have to
mix it pretty thouroughly as it has a tendency to "float out".  It is
very, very lightweight.

> What about this?  A full cob wall 2-3' thick - straight cob. 
> Add a 6" layer of vermiculite laden cob to the outside as a
> very thick outer coat?  or even a foot if you like... 

Make it perlite, and do some testing with it as both an inner plaster
and an outer layer.  See how it adheres to the rest of the wall.

I don't know what difference it might make to put it on the inner wall
and the outer - does someone have an idea and an explanation of how it
might make a difference, heat/cooling-and-perceived-comfortwise?

Sounds to me like an idea worth investigating.

Things to be considered include how it adheres to the rest of the wall,
the effects of weathering (if you slather it on outside),
how well the perlite will "stay in solution",
how much perlite to use per wheel-barrow load of cob (or whatever
quantity you are mixing up at a time),
how expensive is perlite in your area and can you buy it bulk?
If you put it on inside, is perlite at all flammable and if so what sort
of gases might it release?  (What IS perlite, anyway?  I know where
vermiculite comes from but not perlite, and I've used both in potting
soil mixes . . .)

Probably other stuff I'm not knowledgeable enough to think up on my own,
too.

Holly ;-D