Rethink Your Life!
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The Work of Art and The Art of Work
Kiko Denzer on Art
[Cob] Re: was tree-sculpted...now tractor cobmudhome at netzero.net mudhome at netzero.net
Mon Feb 23 15:24:25 PST 2004
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
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