[Cob] mixing cob with rototiller

[Dorothy Bothne]

we use the cement mixer also, we're on our second one.
Dorothy


________________________________
From: Kristen Davenport Katz <kristen at boxcarfarm.com>
To: avjyoung at shaw.ca; coblist at deatech.com 
Sent: Saturday, March 2, 2013 10:44 PM
Subject: Re: [Cob] mixing cob with rototiller

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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