Cob: just a couple things I don't understand

[Howard]

As Shannon says, the straw is like the rebar.  It is what gives cob its tensile
strength while the sand and gravels give it its compressive strength and the clay
soil the cement that glues it all together.  Your boyfriend should understand it in
those terms along with the tapering of walls from thick at the bottom to thinner at
the top.

As for a "cob" roof I would say you probably refer to an earthen or adobe roof of
the sort Hassan Fathy is well known for.  (Shannon, what 's the guys name with
CalEarth, I think, who is carrying on that kind of work?)  You need to make dry
hardened "cob" bricks that you can then lay up into a dome shape.  When Shannon says
she knows of no "cob roofs" she is referring to the specific method of cob
construction that deals only with walls in a wet mud monolithic manner which would
be difficult to build a dome with, at least without a form.  But cob is earth, sand
and straw just as the adobe bricks that have formed domed roofs are.  This method of
dome building comes from very dry regions where they don't have timber with which to
build a roof and if the current desertification of the planet continues we may all
be from a very dry region..  In the mean time, we can design and build what is
appropriate for our region so that we don't have to go to greater lengths to
waterproof etc.

Howard

"Shannon C. Dealy" wrote:

> 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.
> dealy at deatech.com     |          - Custom Software Development -
>                       |    Embedded Systems, Real-time, Device Drivers
> Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
>    or: (541) 451-5177 |                  www.deatech.com

--
Howard Switzer
2411 Elliott Avenue
Nashville, TN 37204
615-383-4793
www.ecoarchitech.net
http://tn.greens.org/

“Deception is the art of kings.”

“Reality itself has become radical.  To speak on its behalf is a form of
insurrection.”

“There is no way to peace, peace is the way.”

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As Shannon says, the straw is like the rebar.  It is what gives cob
its <u>tensile</u> strength while the sand and gravels give it its <u>compressive</u>
strength and the clay soil the cement that glues it all together. 
Your boyfriend should understand it in those terms along with the tapering
of walls from thick at the bottom to thinner at the top.
<p>As for a "cob" roof I would say you probably refer to an earthen or
adobe roof of the sort Hassan Fathy is well known for.  (Shannon,
what 's the guys name with CalEarth, I think, who is carrying on that kind
of work?)  You need to make dry hardened "cob" bricks that you can
then lay up into a dome shape.  When Shannon says she knows of no
"cob roofs" she is referring to the specific method of cob construction
that deals only with walls in a wet mud monolithic manner which would be
difficult to build a dome with, at least without a form.  But cob
is earth, sand and straw just as the adobe bricks that have formed domed
roofs are.  This method of dome building comes from very dry regions
where they don't have timber with which to build a roof and if the current
desertification of the planet continues we may all be from a very dry region.. 
In the mean time, we can design and build what is appropriate for our region
so that we don't have to go to greater lengths to waterproof etc.
<p>Howard
<p>"Shannon C. Dealy" wrote:
<blockquote TYPE=CITE>On Sat, 28 Sep 2002, Angy Violet wrote:
<p>>
<br>> So, my boyfriend specializes in concrete, and I am trying to explain
<br>> cob to him, and he can't quite compare it to what he knows. He doesn't
<br>> understand why you wouldn't need rebar in the walls!!!! He claims
that
<p>The straw performs a function similar to rebar, straw is extremely strong
<br>when used in quantity, and cob is about 10% straw.
<p>> there has to be some giant support system I don't know about. Like
the
<br>> roof, I know that you can make a grass, shake, metal, or post and
beam
<br>> roof. But there are also cob rooves, and how are you supposed to
mold
<p>I don't know of any instance of a cob roof, and would highly recommend
<br>against trying it.  Cob is extremely heavy, and while it is conceiveable
<br>that one could build a roof with cob, it would have to be water proofed
<br>in some manner, and if the water proofing failed, the roof could easily
<br>soften and collapse killing everyone inside.
<p>> something while its supporting you, and if there were no supports,
<br>> wouldn't it just fall down?! One more thing that doesn't make any
sense:
<br>> cold joists. How can you build half of a wall, and then quit for
the
<br>> day, and restart the next day? Wouldn't the top half just fall right
<br>> off? Do you have to build the whole house in a day????!!! Please
help!
<p>I'm not sure what you are asking here, walls are generally vertical,
you
<br>are layering the cob up vertically to form a wall typically about 18
to 24
<br>inches thick, why would you expect it to fall over?  Actually,
you
<br>typically can't build cob higher than 8 to 12 inches each day because
the
<br>weight of the cob will cause it to slump, it needs some drying time
to
<br>allow the lower layers to harden somewhat so they can support the weight
<br>of the higher layers.  New layers typically will bond readily
to a layer
<br>which was built anytime in the last few days because it takes a long
time
<br>for cob to really dry, and there are various techniques which are used
to
<br>deal with situations where it may be weeks or months between two layers.
<p>Shannon C. Dealy      |              
DeaTech Research Inc.
<br>dealy at deatech.com     |         
- Custom Software Development -
<br>                     
|    Embedded Systems, Real-time, Device Drivers
<br>Phone: (800) 467-5820 | Networking, Scientific & Engineering Applications
<br>   or: (541) 451-5177 |                 
www.deatech.com</blockquote>

<p>--
<br>Howard Switzer
<br>2411 Elliott Avenue
<br>Nashville, TN 37204
<br>615-383-4793
<br>www.ecoarchitech.net
<br><A HREF="http://tn.greens.org/">http://tn.greens.org/</A>
<p>“Deception is the art of kings.”
<p>“Reality itself has become radical.  To speak on its behalf is
a form of insurrection.”
<p>“There is no way to peace, peace is the way.”
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