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The Work of Art and The Art of Work
Kiko Denzer on Art

[Cob] Rototiller

Henry Raduazo raduazo at
Wed May 14 21:02:24 CDT 2008

I have mixed many tons or cob with a tiller.  When I built a cob wall  
in my house I mixed and moved 8 tons in eight days with one or two  
assistants, but these were not consecutive days. Mixing with a tiller  
requires that you make cob that is a little wet, so I mixed and  
placed a ton then let the wall dry or set for a couple of days, Then  
I mixed and placed another ton and let it set. One time I had to let  
the wall set for seven days before I could continue building, but  
this is a small price to pay for being able to mix up 2000 pounds of  
cob in one hour with just two people.
	The technique that I used was place the sand and clay on a slab  
create a shallow well in the center filled with water, then dive into  
it with the tiller. One person mixed and spread the mix while the  
other person piled up the clay using a sand shovel to scrape the mix  
off the slab. In short order I had a mix of heavy wet slop to which I  
added chopped straw.
	Note: I use a cheap five horse power front tine tiller.  I can crash  
the tiller into a pile of dirt and pull it apart as I move around the  
pile while my assistant recreates the pile with a shovel so I can  
tear it apart again.
	The straw was coarsely chopped by laying flakes out next to a wall  
and running a lawn mower over the flakes to throw the flakes against  
the wall. Note: Wear an N-95 or better dust mask and eye protection  
when you do this. The chopping is to keep the straw from winding its  
self up on the tines of the tiller.
	The straw thickened and dried up the wet clay enough so I could  
stack it well over a foot with out slumping. I picked up the cob and  
moved it into a wheelbarrow using the shovel and made cobs of sort  
when I removed it from the wheelbarrow to the wall. If you should  
make a batch that is too wet let it set a day and then move it to the  
wall when it has dried to the right consistency.
	I have done the same thing using the tiller to both mine and mix  
clay at the same time only using a dirt fork and steel toed shoes  
instead of a sand shovel to move the mix from the ground to a  
wheelbarrow. (I spear the mix on the ground with the dirt fork and  
then use the steel toe of the shoe as a pivot point to pry the thick  
mix out of the pit.)
	I am an old man and if I can mix and move 2000 pounds in one day you  
young folks should be able to double or triple that.

On May 14, 2008, at 3:20 PM, Damon Howell wrote:

> Hi Mitch,
> 	I tried the rototiller once for about a minute then quickly decided
> it took just as much energy as mixing it with a tarp. But I was only
> mixing a a small batch of, say, 10 gallons, and the tiller would just
> throw the cob everywhere (Very discouraging!) I imagine if you do
> more like 100 gallons (so you could really dig the machine in) it may
> work better. I also tried driving over it with a four wheeler, but
> all my clay just stuck to the tires. So far, the best way I've found
> is the tarp method, unless you want to mix it really wet and let it
> sit for awhile to stiffen up.
> Damon in GA
> Message: 5
> Date: Tue, 13 May 2008 09:04:52 -0500 (CDT)
> From: Mitch Ventura <h_anpyp at>
> Subject: [Cob] Rototiller
> To: coblist at
> Message-ID: <269377.82351.qm at>
> Content-Type: text/plain; charset=iso-8859-1
> Am still gathering as much info as I can on cob building prior to my
> cob project sometime in late 2010 (when I should be finished here in
> Iraq... still a perfect region for cob but may not ever see that
> technology, ironic as that may seem); this Forum has been a great
> source for data and links to other sites (my thanks to almost  
> everyone).
>    Anyway, came across the following website that had a few twists on
> views that I have previously seen written and argued on in this Forum:
>    Never thought of using a rototiller (and would have relegated it
> to the same negative views that I read on cement mixers).
>    The use of added straw may not be good for me as I maintain a
> residence in a subtropical climate (great for bacteria, mold,
> termites, and other organic consumers).
>    Wonder if the more technically inclined members of this Forum
> could voice their opinion on the rototiller and added straw...
>    Ma'a salama.
>    Mitch
>    (somewhere near Sadr City, Baghdad, Iraq)
>    P.D. Fellow firefighters laugh at me all the time as I am a bit of
> a tree hugger, but a realistic one at that... sure the rototiller
> uses some gas, but how many of us have guzzled gallons of fuel in
> order to attend an eco-seminar far from home? (LOIL... Lots Of Ironic
> Laughter)
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