Cob: responsibilities and the machine

[SANCO Enterprises <Paul & Mary Salas>]

Mike Carter and Carol Cannon wrote:

>
> Paul, it takes us less than 25 days to mix, move, and place that much cob
> with 3 people.  Where are you getting your "straw man" numbers (period of
> several years) from?  The cob is only 20-30% of the effort (cost if you are
> paying for help) in the building, anyway.  I agree about mixing and moving
> large amounts of the stuff being dulling, but in our experience it is only a
> few hours work out of the day.  I have been in several situations where
> experienced cobbers see making the cob as beneath them; some even vocalize
> that they will help out as long as they don't have to make the material.
> Here, I have heard that rammed earth suffers from the same problem, leading
> to high employee turnover.

Most owner-builders are not experienced nor is their help if they are fortunate
enough to get it.  If you take the 25 days of full time work noted in your
example it equates to 6 months of weekends.  Factor in a learning curve, no
shows with the help, weather delays, it easily becomes a year, 18 months or even
2 years.  Your example illustrates that to build efficiently, it must be worked
full time and with experienced help.

>  Contractors here in Austin have speculated about using carousel-type stucco
> pumps for cob;  there were problems of aggregate size (requiring expensive
> pre-sifting of the ingredients) and inability to handle straw that needed to
> be overcome.  I know your design is different.

I agree that the peristaltic or carousel pump will not work because it squeezes
the material within a flexible hose. There would tend to be a build-up of the
longer shaft straw within the pump.  The Moineau or cavity pump design is very
similar to the hand cranked meat grinder where the material is fed into the
screw and pushed rather than squeezed or plunger rammed as in a hydraulic
concrete pump.  In the Moineau design, the steel exterior body houses a rubber
insert (stator) that mirrors the screw (armature).  If a stone or other debris
enters the pump, the flexible stator easily deforms to permit the obstacle to
pass through the pump.  Because the earthen material is pushed along through the
pump in several stages, straw and such have no impact on the ability of the pump
to perform.


Paul Salas
SANCO Enterprises, LLC
Albuq., NM