thought on cob chiminney.

[Shannon C. Dealy]

On Sat, 16 Nov 1996 goshawk at gnat.net wrote:

>  Well I've been quite busy working a web site but I have started 
> doing a bit more design work on our spring project (cob building). I 
> have an idear to have a cob chimminey with a cast iron wood burning 
> stove feeding into it. I figure I'll save money over mental piping 
> and the thermal mass of the cob will store the heat better. 

Sounds good, though you may still want to to line the cob chimney with
either stove pipe or fire brick.  I am not sure how long the cob will hold
up in direct contact with the heat and exhaust gases from the fire.

> 
> Did the Cob cottage folks ever get around to doing a hybrd strawbale 
> and cob house??

They have done a few hybrids using strawbale for walls that don't receive 
any direct sun, and cob for walls with solar exposure to store the heat.
I had been thinking of trying to build a cob wall with straw embedded in
the middle to improve the insulation value of the wall, but haven't had
time to try it yet.

> 
> I'm thinking of building some kind of pit to make cob in. I've heard 
> that if the cob sits a day before building that it works better (I 
> guess by works I think they mean more moldable. 
> 
Using a pit is a more traditional way of making cob.  Some of the
advantages of the pit is that if you have some type of cover, it will help
to keep the cob from drying out if you need to store it for a few days,
and it is easier to make large batches.  You will probably want to line it
with something (large heavy duty nylon tarp?) in order to keep the cob
from adhering to the bottom of the pit.  One disadvantage of large batches
is that it is more difficult to thoroughly mix the cob and get a uniform
mixture.

Letting it sit for a day probably helps because it gives the water time to
work its way into all the small clumps of clay.  I have found that it is
easier to mix cob if you let the water soak into the earth mixture for a
while before you start working it with your feet because the clay lumps
break down more quickly.  Once the cob is mixed, it may also help to let
it sit for a while to allow the straw time to absorb some of the water
which should make it more flexible and easier to work.

Shannon Dealy
dealy at deatech.com