Cob cob / ceramics

[Lars Fields]

goshawk at gnat.net wrote:
> 
> > lars wrote:
> >        this is kind of an aside - maybe pat newberry might know best:  does
> > anybody know why it is inappropriate to mix straw with clay if one is making
> > bricks for a fired structure 'a la nader khalili'?
> 
> Remember Superadobe and Nader's fired sturctures are two different
> animals. You can use straw in superadobe (I often do at the ends of
> bags) but I've never seen any pottery or fired bricks with straw so
> my guess is that the straw would disintergrate and the weakend
> structure would still not gain that much in insulation value from the
> air pockets.

	i understand the difference between the two. sorry if i caused any 
confusion, though. 

	pat: why do you use cob at the ends of the superadobe bags? 

	and back to theory: yes, N. khalili _does_ specifically state that one 
should not mix straw with bricks that are going to be fired, but he never states 
why. i'd just like to know the reason. he does talk about using a wood member 
embedded in the wall which would then completely burn out when the structure is 
fired, leaving a conduit for electrical lines or plumbing. this also helps assure 
that the heat reaches deep into the wall and evens out the firing process. 
	i was imagining using the same technique, but on a smaller scale. where 
the pieces of straw burn away leaving myriads of air pockets. if one fired a cob 
structure made out of the right proportions (whatever that might be) of clay and 
straw, then maybe one would get a lightweight, water-proof, semi-porous (high 
insulation value) material - kind of like making your own pumice on site. it 
might also help ensure even firing of the wall, allowing the heat to more easily 
reach deep into the thick walls. 

	waddya all think? fired cob? hmm.... or maybe fired wattle-and-daub, or 
firing bricks made from woodchips and earth. anybody out there ever fired a cob 
structure? i think the ratio of earth to straw/woodchips might be critical (if 
the idea had any chance of working anyway, which i'm not convinced it would). 

just some crazy thoughts.

lars fields