[Cob] The matter of insulation. :)

[Shawn King]

Actually, no bales, loose straw dipped and rolled in slip, squeezed to
get the excess slip out, then plastered on in small lifts, much like
cob, but WAY faster to mix and apply than cob.  I have a ball of the
stuff I made about the size of a tennis ball and I can stand on it
without cracking it.  It can certainly support its own weight, maybe
not a heavy roof load, tho the cob walls should do that on their own.
I think unless you have curved walls, 12 inch cob is a minimum, more
is fine but likely not needed. So cob on the inside and clay straw on
the outside, one thick layer of each, cob first, then clay straw.
Ideally, if your foundation is wide enough, leave 2-3 inches on the
outside edge of the top surface uncobbed, so you have a little shelf
to start the clay-straw on.  If you have a full 18 inch wide
foundation/stem wall, go 12 inches of cob and 8 inches of clay-straw,
gently tapering outward at the base from 6 inches to 8 inches of clay
straw. In our house, we have a narrow stem wall and foundation, so we
put forked branches pointing outward from the cob wall at the base,
stuck into the wet cob, to give a bit of extra gripping capacity for
the future clay-straw layer. Clay straw is very light when it is dry,
heavier than foam but much, much lighter than cob, it will not put
that much more load on your wall. I bet you it would support a roof as
well as bales do.

On Tue, May 10, 2011 at 8:35 PM, Mike <aspiringbodhisattva at gmail.com> wrote:
> VEEEERRY interesting, Shawn!
> So you're basically doing a straw bale system with the bales super saturated
> with clay, huh?  I guess I worry a little about the compressive strength
> (enough for 12' walls?  and bearing a roof load?) - what are your thoughts
> about that?  I'm expecting the wall to be about 18" thick... so you're
> saying a base thinner wall of cob and then packing claystraw?  What's the
> layering you have in mind?
> And sand-clay-horse manure is exactly the plaster I had in mind.  Perhaps a
> lime mix as well for color and strength, but we'll see.
> R2/1" isn't so bad, really.
> Lot of "workshops" going up these days. :)
> On Tue, May 10, 2011 at 11:26 PM, Shawn King <sbkingster at gmail.com> wrote:
>>
>> Hi Mike, I have built an earthen oven insulated with clay-straw, and
>> it works very well to stop the transfer of heat.  I found some
>> research that clay straw is roughly R 2 to R 2.5 per inch, not far off
>> ubiquitous pink fiberglass.  When dry, the stuff is very tough, like a
>> connective tissue on the outside the cob. Basic earth plaster works
>> really well for a final coat (clay/sand/horse manure in the case of
>> the oven).  My partner Melissa and I are building a small cob
>> "workshop" in our suburban back yard and plan to use clay-straw to
>> outsulate the walls. You can start the layer thin just below the top
>> of the stem wall and curve it outward as you add upward so you get to
>> 6-8 inches of thickness.  If your cob walls are 12 inches thick
>> (roughly R 6 but that don't mean much), by the time you finish plaster
>> you may have R 20 conservatively, plus all that lovely thermal mass on
>> the inside, your walls still breath, and you can get it all done with
>> local and cheap or free stuff.  No, I haven't tested this idea on a
>> house, but if I can get my earth oven up to 700 degrees or so and the
>> outside of it is cool, with about 5-6 inches of straw clay as the
>> insulation, I think it would work well enough for a house.
>>
>> Best, Shawn King
>>
>> On Tue, May 10, 2011 at 7:41 PM, Mike <aspiringbodhisattva at gmail.com>
>> wrote:
>> > Hi folks!
>> >
>> > I'm in Chapel Hill, NC, where I've gotten permission to build a small
>> > cob
>> > workshop in my backyard (12x12x12 max, since they're not going to
>> > inspect
>> > the cob - just the electrical and plumbing I'll run to it).  Got the
>> > foundation and drainage trench dug and just about filled.
>> >
>> > I (shh) am hoping to be able to stay in this "workshop."  I'm curious
>> > what
>> > options might fit cob Besides straw bales... I'm not a total purist (at
>> > least this time), and, for instance, lined the foundation trench inside
>> > out
>> > and out to grade with R-5 1" thick solid foam board... more out
>> > of curiosity than belief it's the right application. :) Has anyone had
>> > any
>> > experience adding a modicum of insulation into cob - I've heard of
>> > sandwiching foam board slices with wire to hold it together in the cob
>> > walls, though I worry about anything that might lessen the monolithic
>> > quality to the walls.  And while one cob book mentions you can plaster
>> > foam
>> > board, I just can't see that working with how the boards resist
>> > moisture.
>> >  Just curious, any hybrid thoughts?
>> >
>> > Best wishes,
>> > mike
>> >
>> > --
>> > -------------------
>> > "The greatest achievement is selflessness.
>> > The greatest worth is self-mastery.
>> > The greatest quality is seeking to serve others.
>> > The greatest precept is continual awareness.
>> > The greatest medicine is the emptiness of everything.
>> > The greatest action is not conforming with the worlds ways.
>> > The greatest magic is transmuting the passions.
>> > The greatest generosity is non-attachment.
>> > The greatest goodness is a peaceful mind.
>> > The greatest patience is humility.
>> > The greatest effort is not concerned with results.
>> > The greatest meditation is a mind that lets go.
>> > The greatest wisdom is seeing through appearances."
>> > ~Atisha
>> >
>> > "Most of the luxuries, and many of the so-called comforts of life,
>> > are not only not indispensable, but positive hindrances
>> > to the elevation of mankind. With respect to luxuries and comforts,
>> > the wisest have even lived a more simple and meagre life than the poor."
>> > ~Henry David Thoreau
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>
>
>
> --
> -------------------
> "The greatest achievement is selflessness.
> The greatest worth is self-mastery.
> The greatest quality is seeking to serve others.
> The greatest precept is continual awareness.
> The greatest medicine is the emptiness of everything.
> The greatest action is not conforming with the worlds ways.
> The greatest magic is transmuting the passions.
> The greatest generosity is non-attachment.
> The greatest goodness is a peaceful mind.
> The greatest patience is humility.
> The greatest effort is not concerned with results.
> The greatest meditation is a mind that lets go.
> The greatest wisdom is seeing through appearances."
> ~Atisha
> "Most of the luxuries, and many of the so-called comforts of life,
> are not only not indispensable, but positive hindrances
> to the elevation of mankind. With respect to luxuries and comforts,
> the wisest have even lived a more simple and meagre life than the poor."
> ~Henry David Thoreau
>