[Cob] mixing cob with rototiller

[bill@auburnacupuncture.net]

Hi, 
Have you considered, "bale-cob"? Or do you need the thermal mass of straight cob? What about timber frame with bale-cob in-fill?

I am starting a project of the the latter design this year. The plan is to be done by Fall rains - Dao willing :-)
$.02
Bill

Sent from my Verizon Wireless 4GLTE smartphone

----- Reply message -----
From: avjyoung at shaw.ca
To: <coblist at deatech.com>
Subject: [Cob] mixing cob with rototiller
Date: Sat, Mar 2, 2013 8:37 pm


Chiming in here because we have experience of mixing with rototiller and small digger.... We borrowed a small digger with tracks, an arm, and a bulldozer blade from a neighbour for $25CDN an hour and parked it at our place so we could use it whenever we needed. We used the scoop as a measure for making cob, and ended up with a pit in the driveway to help contain the cob so it didn't spread all over, then scraped it out when done so it was easier to access. Eventually the neighbour needed it back, so we got a second-hand rototiller. We built a platform about 9' x 9' from thin scrap wood and that works fine to prevent the tines and cob from disappearing into the earth. The tines need cleared of long straw sometimes, and I mix a bit more straw into the cob manually as the rototiller doesn't seem able to get quite enough in. I think you can blunt the tines with an angle grinder if they are chopping through the straw too much. Rototiller cost $50CDN.

Amounts; mixing a small batch with a digger (one scoop clay, two pumice, two sand, straw and water to taste), gives a lot of cob. We had layers of tarps over it in the shade to stop it drying out and  sprayed it with the hose when it felt too dry. It was good for doing walls with, when I was getting through a lot of cob very quickly. With the rototiller, we mixed using a wheelbarrow as a measure. It ends up quite wet, more so if you don't cover it with plastic against the winter rains. I put a load in a wheelbarrow at the front and keep a flake of straw at the back, and mix a handful of straw into every fork load of cob. I think this helps counter straw rot from the longer drying time in winter, and helps to dry it out a bit. Still wetter cob, but smaller quantities, which works well for the interior furniture and walls I am doing at the moment. I just do multiple thin lifts to let it dry enough.

Cost; if you can figure something out like our arrangement with a neighbour, it's way cheaper than a hire from the tool rental place. The one time we did this, it worked out about $100 an hour for a little bobcat. You only need it for 3-4 hours to mix a batch, but still have to pay all the delivery fee etc. A rototiller is cheaper again, and doesn't usually make more than one person can easily use, so it's not sitting too long.

Overall, I would rather do either than mix by hand, as there are just so many other things that need done to build a house / raise a family, and mixing by hand is very time consuming. We are keen to get done so we can move in, after 7 years building so far, so saving time is getting more and more important for us.

Hope this helps your decision-making,

Anna
cob/bale timberframe in Victoria, BC



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