Cob cob and cisterns

[Lars Fields]

Vernon B. Johnston wrote:

<snip>

>     Smaller cob projects seemed within my range for this year, so I built a
> foundation for a cistern and for a sweat.  I hope to have both of them
> completed by the end of November.  If there is interest, I will send more
> info on the cistern at a later date.

i'd appreciate any info on cob and cisterns. 

	 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'? i was wondering about 
methods for air-entrapment with ceramic structures - i thought maybe firing a 
cob structure might result in a strong, water-resistant but relatively 
light-weight semi-porous (ie. higher r-value) ceramic structure. or does the 
straw expand too much when it is burning, causing the clay/adobe to crack? 

	the reason i mention this is that i was wondering whether the steam 
from the sweatlodge might saturate the cob with so much moisture that the 
building would slump after a while, reducing the strength of the dome. i've 
never built anything with cob, i was just curious whether you thought this was 
a valid consideration. i'm trying to get a feel for how the material behaves 
over time. i would imagine (based on no experience whatsoever) that cob in a 
humid environment would act like wax in warm environment - that it would 
basically melt, but really slowly. what do y'all think? 

	i'm especially interested in the possibilities of using n. khalili's 
methods for producing ceramic structures for creating water cisterns or even 
methane digesters. or what other ways are available to make airtight/watertight 
containers other than metals, plastics or concrete? 

thanks 
lars fields