[Cob] Cob mixing tests

[Shannon C. Dealy]

On Fri, 23 Jun 2006, Susan Evans wrote:

> Has anyone tested the various cob mixes?  There seems to be a lack of 
> definitions on the mailings - hand-mixed cob is deemed superior to machine 
> mixed. Surely this does not mean my poor hand-mixing is superior to a 
> machine-mixed batch that I have spent a reasonable quantity of time 
[snip]

When I say that the machine mixed cob is inferior in my earlier post, it is 
based on my experience using cob mixed mechanically by myself and many others 
using large tractors with a bucket loader, rototiller, and bobcat/skid loader 
mixing.  In this context I mean that mechanically mixed suffers from the 
following problems which do not occur in foot mixed cob:

   - Straw clumps
   - Unmixed clumps of soil
   - Lack of uniform mixture
   - Skewed mixture ratios if you mix on bare ground because you are not
     able to mix on a cement pad or similar surface.

Except for the last one, these are obvious problems that you can see while 
applying the mix to the wall.  The straw clumping problem could be reduced or 
eliminated by using shorter straw, at the expense of reducing (possibly 
significantly) the tensile strength of the cob.  All of these problems showed 
up regardless of the technique used and how experienced the person using the 
equipment.  None of these problems is a show stopper, you simply create a 
discard pile and toss the worst of the problem cob into the pile for mixing 
with the next batch, though it will slow you down a little bit in your 
application of the cob.

Nothing I have said was intended to discourage people from using mechanical 
mixing, I merely wished to illustrate that the expected time savings was 
nowhere near what people might be expecting, but it is still a significant time 
savings, and I have on occasion used it, though if I have the time I 
definitely prefer to use foot mixing.

FWIW.

Shannon C. Dealy      |               DeaTech Research Inc.
dealy at deatech.com     |          - Custom Software Development -
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