[Cob] Roto Tillers and Cob?

[Whidbey Island Soap Co.]

Wow! Thanks for the info. I will give this a try.

This might work too! how about having two lines of cement blocks which you
fill with clay between them then add the sand on top and begin mixing. Then
add the straw to it. This way you do not have to shovel things to the center
and it all stays in one spot for mixing. Then you use a shovel and pick out
the cob from between the rows of cinder blocks and pile it on the wall.
sound good?

Anyone ever used forms to hole a layer of cob one the wall?

David T
  -----Original Message-----
  From: Raduazo at aol.com [mailto:Raduazo at aol.com]
  Sent: Wednesday, June 21, 2006 7:27 PM
  To: soap at whidbey.com; coblist at deatech.com
  Subject: Re: [Cob] Roto Tillers and Cob?


  In a message dated 6/21/2006 2:19:54 A.M. Eastern Standard Time,
soap at whidbey.com writes:
    Ok! Some one please enlighten me on how you use a roto tiller to make
COB. I need a way to make cob quickly and efficiently and this sounds like a
possibility.

    Thanks

    David T

  David: I am currently working on an article that I plan to submit to The
Cob Web and to The Last Straw on tiller cob. The article is pretty much
written. Now I just need photographs to go with it and I should get them
this weekend. The article is as follows:

  Tiller Cob by Ed Raduazo
       Foot mixing cob to Build a house is just the sort of thing I might
have done back when I was 18 or 20 years old and unemployed, but now that I
am 65 and suffering a few joint problems getting out a tarp and mixing up a
ton of cob is not just a hard day's work, for me it is darned near
impossible. It makes one ask don't they make machines for doing that? Well
it just so happens that they do make machines for that. They are called
rototillers. Tillers are designed for turning up dirt and well that is
pretty much what we are doing isn't it. But there are a few adjustments that
you have to make in order for this to work.
       The first is using chopped straw. The tiller has a rotating blades
and if you attempt to use long straw many of the strands will wind them
selves around the tiller shaft and you will spend half the time cleaning the
blades.
   Some of the bailing machines chop the straw as they bail it, but I have
never been able to find straw that was pre-chopped to my liking and have
always had to make it. Being an old time gardener of course I have a leaf
shredder, but the leaf shredder tends to shred the stuff too fine. The finer
stuff would probably work and in fact it reminds me of the straw for "window
cob" or straw for earth plaster that Ianto had me manufacturing when I took
his class in British Columbia.
       What seems to work better and faster than a leaf shredder is a cheap
side discharge lawn mower. Preferably one with a real sharp blade. I simply
lay out a series of flakes along side of a wall, and lowering and raising
the handle of the mower as I approach each flake will shred it and throw it
against the wall.
       Note: Rotary lawn mowers were not designed to be used as straw
shredders. Protective eye wear and a P-95 or N-95 rated dust mask are
mandatory accessories if you plan to do this.
       The tiller you use needs to be one of the cheap tillers with front
tines. Small light weight is also a plus, but with plenty of power to drive
the tines.  I was once given a Troybuilt rear tine tiller at the National
Building Colloquium-East and could not make it work. You need to be able to
go forward and backward and make really sharp turns on a small pile of dirt
and the rear tine tiller would not do that. The rear tine tillers have a
metal plate to protect your toes from getting chopped off and this plate
prevents you from pulling the tiller back and forth and prevents sharp turns
needed to go back and forth across the pile.
        My first tiller was a 5 Hp chain drive tiller that was fantastic. It
could power its way through the thickest glop so that when I was finished
tilling I was finished. After I wore out the engine on that one though I
inherited my Dad's gear drive tiller. Actually it is a belt drive that goes
to a drive shaft that goes to the gear box and drives the tines. This is
also 5 Hp, but the belt portion of the drive system tends to slip when I run
it into really thick cob/sand/straw mix. It still works, but I usually end
up adding a little more water than I like or just doing the dry mixing and
finishing on the tarp. It still saves you a tremendous amount of time.
       More water makes the cob softer so you are limited to 6 inches to 1
foot of construction in a day and you need two or more days of drying out
before you can put on the next layer. This can work out fine. If you are a
small crew on a large project, it will take a couple of days to work your
way around the wall and get back to the starting point, or if you are a
weekend cobber like me you can do couple tons on Saturday and Sunday, and
your wall has five days to dry out before the next couple of tons gets piled
on.
       Selecting the mix is pretty much the same as with foot stomping. More
clay means a stickier mix that will shrink more. More sand means less
shrinking less sticky. I usually go rich on the clay because that is the
free ingredient of my mixes, and because if the mix is too wet, I can do a
lot of compensation by adding straw. Whereas if the mix is rich in sand and
I try to add straw to compensate for a wet batch the stuff will not stick
together.
      My preferred mixing surface is a concrete slab. (Be careful on asphalt
slabs particularly cracked asphalt as the tiller will break up the slab and
add it to your mix.) The slab surface gives you complete control of your mix
ingredients and your mix size. I like to work with batches of about one ton.
This is 10 of the deep wheelbarrows filled to the top. When I did my solar
storage wall I used 5 wheelbarrows of sand and 5 of clay. In the playhouse
job at Clarindon we have very sandy clay so the mix is 3 sand and 6 clay. I
pour the clay and sand out on the slab in alternate layers to a depth of
around 6 inches and work around and across the pile then I add straw and do
it again. It is good to have an assistant with a shovel who can pick up clay
or sand rich material from the edges of the pile and throw it into the
center.
       When the pile looks fairly uniform, I create a well in the center by
letting the tiller turn in place for a while and pulling back to drag the
center material towards me. Then I fill the well with water and begin mixing
again. I find it easiest to turn the center into a batch of gooey slop and
then have my assistant throw in shovels full of dry stuff from the edges and
then add more water with the hose till I get what I want. Here is where a
good power to blade size ratio really helps. With my old tiller I could mix
really thick sticky cob that would not slump very much, but with my new
tiller the belt slips when the going gets too tough. I was thinking about
removing the outer two blades but the tiller is so old that I am not sure
they will come off or that I could get them back on.
       With a tiller it is easy to adjust the moisture content by throwing
in more straw or clay or sand if you need to dry out stuff that is too wet,
or by spraying water on areas of the pile that are too dry.
      In one of my jobs I did not have a concrete slab to work on and I used
the tiller for both mining clay and mixing cob. I did this by just throwing
sand out on the ground and using the tiller to bring up enough of the
compacted subsoil to make the mix feel right. The main difference is that
you will use a dirt fork instead of a shovel to move the finished material
up out of the pit and into the wheelbarrow to go to the wall.
       Even with tiller mixing cob is a heavy labor intensive building
material. Use it wisely. I have been reading The Solar House (Passive
Heating and Cooling) by Daniel Chiras, and I believe that the future of cob
is as a structural component and heat storage means used in combination with
straw bale and glass curtain walls. You can enclose a lot of space with
bales quickly and you have a great insulator. With cob and stone you have a
great heat storage means and load bearing means. With a post and beam and
glass curtain wall you have a great heat collector. They can work together.
      If you have questions and/or comments or proposed editorial changes
please send them to me, not to the coblist. If I like them I will
incorporate them into the article before I submit it.
      I can not send the pictures through the coblist so if you want
pictures please send me a separate E-mail sometime next week and I will try
to gather up every one who wants a picture and send them all out at once. (I
have dial up so you know what that is like.)  raduazo at aol.com