Cob: RE: small cob housing

Thu Jul 3 17:28:57 CDT 2003

Some people have tried cement mixers to mix cob but the standard drum style
mixer just isnt a good tool for the job and you end up being able to mix
cob with your feet faster. A mortar mixer works much better but still ends
up with a wet mix and the straw has to be mixed in manually or it fouls the
blades. Basically what you need to do to mix large amount of cob is to
replicate the trodding action of foot mixing.

Traditionally cob was made in an animal lot over time, allowing animals cows
and or horses to trod over an area for months pressing the elements together
like kneading dough. We now try to replicate this with our own feet and a
tarp. It takes a lot of work to make relatively small batches. The best way
to mimic this process with machines is quite simply replacing horse hooves
with horsepower. This is often done with a tractor (hence called tractor
cob). Ive found personally that the very best small-scale cob mixing unit
is a bobcat. The bobcat because of its counter rotating wheel steering can
simply spin in place around the clay/sand/straw mix, churning it squishing
it together under the weight of the unit. The added benefit of the front end
loader on the bobcat to both scoop the mix back into a pile and then deliver
it within reach of folks working on an elevated wall section make it a great
tool to have. It also fits well in a tight building site. You can of course
use a standard tractor or even a truck but they both have drawbacks (the
truck in particular) The important aspect of mixing cob though is that the
individual elements have to be compressed together to get everything to bind
well. Tumble mixing will never get you a really well bonded mix. Save the
cement mixer for the lime plaster. It works great for that.

On the topic of pouring cob
 well, its not really cob at that point. Cob
takes quite some time to dry out and if you had a mix that was wet enough to
pour and you trapped it inside forms Im afraid it would take months to dry
enough to support its own weight to allow the forms to be removed. Im
guessing here since Ive no experience at all in that area. When I discussed
building cob relatively quickly please note the relatively aspect. There
is still a drying time that is needed for each lift to be able to support
more cob above without schlumping :-) (basically collapsing under the
weight of new cob above it). Still, even with that drying time, the home I
spoke of built by Kevin McCabe took only 3 months to build the walls on a
3200 square foot home. The entire project took 15 months with him and 2
other workers on the job. The home was built to a high level of finish as it
was originally built with immediate resale in mind. (he and his wife changed
their minds once it was built and moved in instead). That is the sort of
relative quickly construction I was referring to.

Best of luck with your project however you decide to build it.

Joe

-----Original Message-----
From: owner-coblist at deatech.com [mailto:owner-coblist at deatech.com]On Behalf
Of Mary Hooper
Sent: Thursday, July 03, 2003 10:15 PM
To: coblist at deatech.com
Subject: Cob: small cob housing

Now I'm going to try to send this message to the list instead of just the
one person who brought it up!!!
snip snip snip:::
Cob buildings can be large, they can be made with large machinery and
theycan be made relatively quickly. However, it is also a human scale
technologythat can be made almost completely by hand with simple tools and
.... ::end snip

Now, there's a thought I had not had.... using large machinery.... has
anyone used a cement mixer instead of feet to mix the mud????
I imagine a big truck size mixer and the construction guy saying "You want
me to mix WHAT in it?" and the forms people saying "You want to me to pour
WHAT in my forms?"
Anyone have any wisdom to impart for either sitution? Would a large poured
wall dry without cracking? Would those of us who have tricky knees and
reduced energy levels benefit from thinking "outside the box" on this? Not
to go fully industrial strength, but how could we utilize modern equipment
to make the job easier on our old joints and/or speed up the work?
Mary in NC
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Some
people have tried cement mixers to mix cob but the standard drum style mixer
just isn’t a good tool for the job and you end up being able to mix cob with your
feet faster. A “mortar mixer” works much better but still ends up with a wet
mix and the straw has to be mixed in manually or it fouls the blades. Basically
what you need to do to mix large amount of cob is to replicate the trodding
action of foot mixing.<o:p></o:p>

<p class=MsoNormal><span class=EmailStyle15><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Arial'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></font></span></p>

Traditionally
cob was made in an animal lot over time, allowing animals cows and or horses to
trod over an area for months pressing the elements together like kneading dough.
We now try to replicate this with our own feet and a tarp. It takes a lot of
work to make relatively small batches. The best way to mimic this process with
machines is quite simply replacing horse hooves with horsepower. This is often
done with a tractor (hence called “tractor cob”). I’ve found personally that
the very best small-scale cob mixing unit is a bobcat. The bobcat because of
its counter rotating wheel steering can simply spin in place around the
clay/sand/straw mix, churning it squishing it together under the weight of the
unit. The added benefit of the front end loader on the bobcat to both scoop the
mix back into a pile and then deliver it within reach of folks working on an
elevated wall section make it a great tool to have. It also fits well in a
tight building site. You can of course use a standard tractor or even a truck
but they both have drawbacks (the truck in particular) The important aspect of
mixing cob though is that the individual elements have to be compressed
together to get everything to bind well. Tumble mixing will never get you a
really well bonded mix. Save the cement mixer for the lime plaster. It works
great for that.<o:p></o:p>

<p class=MsoNormal><span class=EmailStyle15><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Arial'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></font></span></p>

On the topic
of pouring cob… well, it’s not really cob at that point. Cob takes quite some
time to dry out and if you had a mix that was wet enough to pour and you
trapped it inside forms I’m afraid it would take months to dry enough to
support its own weight to allow the forms to be removed. I’m guessing here
since I’ve no experience at all in that area. When I discussed building cob “relatively
quickly” please note the “relatively” aspect. There is still a drying time that
is needed for each lift to be able to support more cob above without “schlumping”
J (basically collapsing
under the weight of new cob above it). Still, even with that drying time, the
home I spoke of built by Kevin McCabe took “only” 3 months to build the walls
on a 3200 square foot home. The entire project took 15 months with him and 2
other workers on the job. The home was built to a high level of finish as it
was originally built with immediate resale in mind. (he and his wife changed their
minds once it was built and moved in instead). That is the sort of “relative
quickly” construction I was referring to.<o:p></o:p>

<p class=MsoNormal><span class=EmailStyle15><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Arial'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></font></span></p>

Best of
luck with your project however you decide to build it. <o:p></o:p>

<p class=MsoNormal><span class=EmailStyle15><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Arial'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></font></span></p>

<p class=MsoNormal><span class=EmailStyle15><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Arial'>Joe<o:p></o:p></span></font></span></p>

<p class=MsoNormal><span class=EmailStyle15><font size=2 color=navy face=Arial><span
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<p class=MsoNormal style='margin-left:.5in'><font size=2 color=black
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;color:black'>-----Original
Message-----<br>
<b><span style='font-weight:bold'>From:</span></b> owner-coblist at deatech.com
[mailto:owner-coblist at deatech.com]<b><span style='font-weight:bold'>On Behalf
Of </span></b>Mary Hooper<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, July 03, 2003
10:15 PM<br>
<b><span style='font-weight:bold'>To:</span></b> coblist at deatech.com<br>
<b><span style='font-weight:bold'>Subject:</span></b> Cob: small cob housing</span></font></p>

<p class=MsoNormal style='margin-left:.5in'><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'><![if !supportEmptyParas]> <![endif]><o:p></o:p></span></font></p>

<p class=MsoNormal style='margin-left:.5in'><font size=3 color=black
face="Times New Roman"><span style='font-size:12.0pt;color:black'> </span></font><font
color=black><span style='color:black;mso-color-alt:windowtext'><o:p></o:p></span></font></p>

Now I'm
going to try to send this message to the list instead of just the one person
who brought it up!!! <o:p></o:p>

snip snip
snip::: 
Cob buildings can be large, they can be made with large machinery and 
theycan be made relatively quickly. However, it is also a human scale 
technologythat can be made almost completely by hand with simple tools and 
.... ::end snip 
 
Now, there's a thought I had not had.... using large machinery.... has 
anyone used a cement mixer instead of feet to mix the mud???? 
I imagine a big truck size mixer and the construction guy saying "You want 
me to mix WHAT in it?" and the forms people saying "You want to me to
pour 
WHAT in my forms?" 
Anyone have any wisdom to impart for either sitution? Would a large poured 
wall dry without cracking? Would those of us who have tricky knees and 
reduced energy levels benefit from thinking "outside the box" on
this? Not 
to go fully industrial strength, but how could we utilize modern equipment 
to make the job easier on our old joints and/or speed up the work? 
Mary in NC<o:p></o:p>

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