Cob: suggestions??

[Shannon C. Dealy]

On Thu, 3 Oct 2002, Aile Eagle Bear wrote:

> Thanks for input Shannon.  I suppose a rather ambitious and foolish venture
> on my part here.  I just have no money period, and am trying to get

It's not foolish to try to get by without money on a project, you just
need to understand the limitations of the materials and try to work around
them.  It is possible to do these things without money, and even the
straight cob solution might work, but I am a little concerned about
the combination of pure cob, no chimney liner, and doing it in doors.

> something to work here that would at least benefit my green house and show
> some folks what cob building would do.   I got to point  yesterday of
> realizing that perhaps best thing to do was just put in stove pipe.  So will
> go to salvage yard and see if I can get piping needed.

Stove pipe is not particularly expensive, but if you have no money that
still translates into more than you can afford.  Look for houses being
torn down, check with places that install wood stoves to see if they have
any scraps or old pipe on hand from a system they replaced, check to see
if your area has any centers for recycling building materials, check with
friends to see if anyone has some old stove pipe rusting in their back
yard.  Also, you might consider that it doesn't have to be stove pipe
specifically, heavy gauge steel sheet metal could be formed into a pipe as
well.  You could also see if any stove/chimney place has any clay liners
which are broken that they don't want.  You might be able to tightly fit
the pieces together and hold them in place with cob.

>     There are some folks who have written me and think cob will separate and
> break from heat of wood stove, expanding and all of metal.  Do you feel this
> too?  Am I wasting my time here?  Yes, on straw.,.. I added that in
> yesterday..., thanks for writing me.

The heat will make the metal expand and contract, and it will try to do
this more than the cob will, so there is definitely a potential for
problems here, your best bet is if you use alot of cob anywhere you put
cob around the stove, and it might be better not to try and completely
encase the stove, so that it has some room to expand in at least one
direction.  The bench stoves that Cob Cottage builds (I've worked on three
or four of them), have barrels built into them which will also try to
expand, and based on my experience with them I believe that the reason the
benches don't generally crack (except for maybe the first inch in direct
contact with the barrel) are as follows:

 1 - The cob in contact with the barrel absorbs alot of the heat, keeping
     the barrel from expanding as much.

 2 - The barrel that the cob contacts with is more part of the exhaust
     system, rather than combustion area, so the hottest part of the stove
     (for the most part) is kept out of direct contact with the cob.

 3 - Where the cob surrounds the stove, it usually extends at least six
     inches out, giving it alot of strength.

 4 - The metal of the barrel is relatively thin (compared to something
     like a cast iron stove), so it can't exert as much force on the cob
     when it expands.

 5 - Usually at least half the barrel is left exposed, which allows it to
     expand upward and probably significantly reduces the outward pressure
     that would be put on the cob if it was fully enclosed

 6 - Usually the stove is fired up to help dry/set the cob, this means
     that if the stove is going to expand, it will initially be expanding
     into wet cob which should push out fairly easily, and then it will
     harden while the stove is at least somewhat expanded, leaving a
     little bit of permanent room for the stove to expand into each time
     a fire is lit.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
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Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
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