Cob Earthship

[Kat Morrow]

>Hi Kat,
>
>Your reply regarding how long it takes to build a cob structure
>intrigues me. Of course I am interested in labor saving devices. A
>cement mixer sounds like a good idea. Could you elaborate on tractor
>cob? Is it mixing all the ingredients on the ground using the tilling
>blades and then scooping it up for building the wall?

As far as I understand the process, one can either use the blade (or
whatever implement may be attached to the tractor, backhoe, etc) or just
drive back and forth through the mix.  Probably some premixing when it is
dry, then one person hosing it down while the other operates the machinery.
Then scoop it up and deliver it to the building site.  The mix is lumpier
than foot-mixed cob as it may contain larger rocks or lumps of earth, but
for walls this is no problems as rocks and other materials are often
incorporated anyway.  In our mixes we don't use much sand but about 5% aged
horse manure and lots of straw are the components added to the clay dirt.

>I understand you can only build a wall 8 - 12 inches per day depending
>on how firm the cob is. But I would also expect if you have enough
>people and/or labor saving devices you could build all exterior and
>interior walls simultaneously for faster overall construction.

We have gone up more than 12 inches (2-3 ft) in a day (just had a report of
6 ft in one day, using rocks to stabilize the wall, no slumping or
bulging), but it does depend on your mix.  I think the high straw content
is why we are able to go higher without slumping.  Yep, with tractor cob,
all people are doing is building and things happen very quickly.  One still
gets the total mud building experience but can spend a lot more time in
actual building.  The overall construction time would be considerably less,
especially if you are well
organized and keep the cob coming......

So, this is my understanding and experience with the process, I'm sure
there are other great ideas out there...

Kat