Cob: just a couple things I don't understand

[Shannon C. Dealy]

On Sat, 28 Sep 2002, Angy Violet wrote:

>
> So, my boyfriend specializes in concrete, and I am trying to explain
> cob to him, and he can't quite compare it to what he knows. He doesn't
> understand why you wouldn't need rebar in the walls!!!! He claims that

The straw performs a function similar to rebar, straw is extremely strong
when used in quantity, and cob is about 10% straw.

> there has to be some giant support system I don't know about. Like the
> roof, I know that you can make a grass, shake, metal, or post and beam
> roof. But there are also cob rooves, and how are you supposed to mold

I don't know of any instance of a cob roof, and would highly recommend
against trying it.  Cob is extremely heavy, and while it is conceiveable
that one could build a roof with cob, it would have to be water proofed
in some manner, and if the water proofing failed, the roof could easily
soften and collapse killing everyone inside.

> something while its supporting you, and if there were no supports,
> wouldn't it just fall down?! One more thing that doesn't make any sense:
> cold joists. How can you build half of a wall, and then quit for the
> day, and restart the next day? Wouldn't the top half just fall right
> off? Do you have to build the whole house in a day????!!! Please help!

I'm not sure what you are asking here, walls are generally vertical, you
are layering the cob up vertically to form a wall typically about 18 to 24
inches thick, why would you expect it to fall over?  Actually, you
typically can't build cob higher than 8 to 12 inches each day because the
weight of the cob will cause it to slump, it needs some drying time to
allow the lower layers to harden somewhat so they can support the weight
of the higher layers.  New layers typically will bond readily to a layer
which was built anytime in the last few days because it takes a long time
for cob to really dry, and there are various techniques which are used to
deal with situations where it may be weeks or months between two layers.

Shannon C. Dealy      |               DeaTech Research Inc.
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