[Cob] Re: cob domes?

[Raduazo at aol.com]

Nearly everyone has heard the story about the man who built a cob dome  and 
was killed in his sleep during a heavy rainstorm. The story is so old and so  
oft repeated that it has reached the status of urban legend. I would like to  
know if anyone has seen pictures of the collapsed dome or has first hand  
knowledge from seeing the dome after its collapse? 
My reason for asking this is that I have a theory regarding cob domes.  The 
problem with a cob dome is that at the peak of the dome the surface is  nearly 
horizontal. This means that water and snow will set on this mostly  horizontal 
surface for long periods of time and soak in, and when the dome  collapses it 
will be only the horizontal center that  collapses. 
If this is the case then that problem has been solved both by the onion  dome 
shape of Moscow and by US patent 4665664 to Brian Knight.  
I met Mr. Knight more than 20  years ago when he came down to my office from 
Canadian. It seems that shingles  do not do well on an almost horizontal 
surface because ice dams cause water to  back up under the shingles and even light 
breezes can cause water to flow gently  up hill under the shingles and into a 
dome. Mr. Knight’s solution was to change  the slope in such a way as to 
depart from the dome shape as it approached the  peak of the structure. 
We cannot send pictures over the cob net but you might be able to get a  copy 
from  
_http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/
search-adv.htm&r=7&p=1&f=G&l=50&d=ptxt&S1=4665664&OS=4665664&RS=4665664_ 
(http://164.195.100.11/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=/netahtml/searc
h-adv.htm&r=7&p=1&f=G&l=50&d=ptxt&S1=4665664&OS=4665664&RS=4665664) 
You need special software  to see and print the pictures. I can send a 
photograph to anyone interested, but  residents of North America will recognize this 
structure as the domes erected by  the highway departments of  Canada  and 
the US to store salt and sand for use during the winter. 
Besides the shape of the dome we can also encourage water to move on down  
the trail by making the dome surface very smooth and treating it with a  
hydrophobic material like boiled linseed oil. 
So far I have tried this only on birdhouses, but I am thinking of moving  up 
to small shed in size. I like the idea of small structures that cost nearly  
nothing. The problem that you run into (in spades of course) is the square cube 
 ratio. The strength of a material goes up as the square of a dimension but 
the  weight goes up as the cube of that dimension. In other words a two-inch 
block of  dirt is four times as strong as a one-inch block of dirt but eight 
times as  heavy. 
Hopefully a small shed will not be as heavy or as life threatening as a  full 
sized structure, and it will not be occupied during rain storms, but if  
smaller structures work out who knows. A zero-cost waterproof roof would be a  
nice thing if we could trust it.