[Cob] mixing cob with rototiller

[Kristen Davenport Katz]

Yep—we put all the stuff in the cement mixer, turn it on, wiggle it a little bit … you get the hang of it after a while, there are settings on the mixer so it can be pointed straight up or straight down , and we kinda shift it around a lot to make sure it all gets mixed together. And then dump it into a wheelbarrow. IT’s awesome. I’m a woman without much upper body strength and myself and some female friends did most of the work on these things. You have to get the mix right… I mean, you pay some attention to how much dirt, straw and water you put in to make the mix right and you don’t overload the mixer. Those are the only things to think about. We just toss the dirt in without screening it—but we do toss out the larger rocks. The small ones just go into the mixer. We got the mixer at Harbor Freight for not much money, I think $350, and it’s been great. I find cob to be incredibly forgiving and I think it’s way easier than other people seem to think it is. It’s so easy we built a cob chicken coop last year. Fun stuff. I learned this from a cool cob guy here in NM who teaches classes and learned from Ianto et al… I had this idea in my head that it all needed to be done by hand to be Authentic and he sorta rolled his eyes and said yeah, sure, if you want to take 5 years to build your 100 square foot bathroom, do it by hand. Or you can get it done in a week with a little electricity. Making cob with a cement mixer is very practical. In order to be sustainable it has to be practical. So I am not so idealistic about it any more, although I certainly see the attraction of doing it the very low-tech way (but frankly, a cement mixer is not all that high-tech or high-powered).

 

Kristen

 

From: bill at auburnacupuncture.net [mailto:bill at auburnacupuncture.net] 
Sent: Sunday, March 03, 2013 8:59 AM
To: Kristen Davenport Katz; coblist at deatech.com
Subject: Re: [Cob] mixing cob with rototiller

 

Thanks Kristen, 
So the cement mixer will do ALL the mixing!? I've seen people make the, "slip" in a C-mixer, then stomp straw into that manually, but you put ALL in ingredients into the mixer successfully!? Any detailed tips to be successful, or just go for it?
Thanks,
Bill

Sent from my Verizon Wireless 4GLTE smartphone

----- Reply message -----
From: "Kristen Davenport Katz" <kristen at boxcarfarm.com>
To: <avjyoung at shaw.ca>, <coblist at deatech.com>
Subject: [Cob] mixing cob with rototiller
Date: Sat, Mar 2, 2013 8:44 pm


We use a cement mixer. We got one for like $350 and it has lasted five years
so far. It definitely  makes the whole thing easier. Once mixed, we dump the
cob in the cement mixer into a wheelbarrow and push it over. We put the
cement mixer as close to the structure as possible so it's not a long haul.
Then you just lift handfuls and add it to the growing cob wall. The hardest
part is pushing the wheelbarrow. It's work, but it's not backbreaking. We've
put up two small structures this way and I wouldn't hesitate to build a
whole house like this. So if you have electricity, you can do this.

Kristen



-----Original Message-----
From: coblist-bounces at deatech.com [mailto:coblist-bounces at deatech.com] On
Behalf Of avjyoung at shaw.ca
Sent: Saturday, March 02, 2013 9:38 PM
To: coblist at deatech.com
Subject: Re: [Cob] mixing cob with rototiller

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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