[Cob] Re: was tree-sculpted...now tractor cob

[mudhome at netzero.net]

Please pardon the untimeliness of this post. I had written most of this 
reply when the troubles with my ISP began [insert long boring frustrating 
story/rant of your choice here].

At 11:00 PM 1/11/2004 -0500, ataraktos at hotmail.com wrote:
>i've been lurking for a while and recently searched online specifically 
>for 'tractor cob'. a few years ago, when i first heard about cob and 
>researched a bit online, i got the general impression that tractor cob was 
>somehow inferior to 'regular' cob.
>
>so, i was quite surprised that the pictures of the beautiful "tree wall" 
>(from potkettleblack.com) were in the results of my 'tractor cob' search - 
>is this wall an example of tractor cob?
[snip]

'fraid not. The cob at  http://potkettleblack.com/natbild/sarahtree/  was 
mixed entirely by bare feet on a tarp, but don't let that discourage you 
from trying other mixing methods.

The wall at  http://www.potkettleblack.com/natbild/takomapark2.html  was 
mixed using a combination of machinery and feet. First the sand and clay 
were mixed together by a rototiller (Ed Raduazo's rototiller, to be 
precise, as he kindly left it there for the duration on the project) then 
it was mixed on a tarp, where the water and straw were added.

The building I worked on immediately prior to that one was done without any 
tarp mixing, though I think a little stomping added in at the right times 
would have actually sped things up. That cob was mixed by some kind of 
tractor thing driving in circles on an old concrete pad while a few people 
ran about adding ingredients ahead of it. When we encountered clumps of 
single ingredients while working on the wall sometimes they were thrown out 
as Shannon mentioned, sometimes I would just spread them out and work them 
in well, sometimes I would look for a complimentary clump (this is all sand 
- oh, there's some pure clay) and mix them together by hand, and I'm sure 
plenty of poorly mixed bits ended up in the wall (especially at times when 
fresh cob was being dumped up onto the wall without regard to whether the 
cobbers were ready for it). When we got near the top of the building and 
quality became more critical we began hand kneading the mechanically mixed 
cob before giving it to the people on top of the wall. Sometime during the 
project I had suggested we do just a little foot mixing after the tractor 
part, but the man in charge (who had no cob experience and never worked on 
the walls) wouldn't allow it. (Any guesses who kept pushing for more speed 
and dumping cob on the walls as soon as it could be mixed and brought to 
the site, even when the architect told him not to?) In any case, the 
building turned out just fine - certainly far far stronger than a 
"conventional stick-built" house.

I don't know why the "tree wall" page came up in your search. The page it 
should have given you is  http://potkettleblack.com/natbild/cob.html  where 
you can see "extreme tractor cob" and a description of how it was mixed. It 
seems a good example of the role luck can play in these things - if you 
happen to live on dirt that only needs straw added to make good cob, in a 
dry climate, have a mother-in-law willing to buy you a backhoe and the 
temperament to actually enjoy loud stinky machinery....

What Mark wrote on that page implies that that first picture was taken 
prior to the wall breaking (due to a gravity-defying shape, not the mix) 
but I wonder if he might be confused about the date of the photo. After it 
broke, it was rebuilt with a less concave profile that held up perfectly 
well, then was left unfinished. All that happened before I got there and 
saw it looking exactly like it does in the picture. Unfortunately there was 
no cobbing during my time there so I can't comment on the process, but all 
the cob there looked sturdy to me, including the wall 
at  http://potkettleblack.com/natbild/dirt2.html

The subject has already been covered pretty well by other people, so I'll 
just add - if you plan to store unused cob overnight or longer, be prepared 
for any surfaces that are exposed to air (including those around voids 
within the cob) to either dry out unevenly or get moldy. If neither 
happens, count yourself very lucky. Ironically, on the "tree wall" project 
I had better luck with saving cob than ever before even though the wall had 
the most trouble drying and grew much more mold (in terms of both quantity 
and variety) than I've ever seen on a cob project. There was never any mold 
on the saved cob until the very end (when the wall was drying far more 
quickly due to better ventilation and more light) and then what little 
there was was barely even visible. A couple factors probably contributed to 
its finally appearing: I started saving more cob longer because it was 
holding up so well, and saving it with more and wetter surfaces exposed 
(within covered buckets). Given the location of the wall, all the other 
construction work going on there, and the available materials, storing it 
in buckets was the only convenient and safe method. In the beginning it was 
just put in in big chunks and tended to sink down, packing itself together 
and becoming difficult to get out of the bucket. Then I decided it should 
be made into cobs before going into the buckets (which were also used to 
transport the cob to the wall) to avoid this and because, as the work got 
fussier and more difficult the higher up it went, having it made into 
proper cobs became very helpful. When I made cobs from dry enough 
mix/knowing they would have to sit for a day or more, I started making them 
wetter on the outside. I did that by dipping my hand water for each one, 
which also kept my hands from getting as dried out and uncomfortable as 
they would have otherwise.

BTW, on another project, cob was transported and stored in big plastic mesh 
trays (like milk crates but shorter and wider). When they were left sitting 
on the dry ground, worms tended to come up through the holes into the nice 
wet cob. I would find them while working on the wall and take them to 
safety. Even though I'm not so squeamish about worms as mold, this was not 
as easy as it sounds. They would not just fall off my muddy hands and, 
faced with dry dirt and sharp grass, would crawl up my hand toward my arm.

Sarah