Cob: Data Please

[John Fordice]

Darel & all,
Well I can't  speak for others, but my experience has been:

Darel Henman wrote:
> 
 good quality straw already cut and ready to go.

Good quality yes, but why cut it ?  I sure don't.
....................
> 
> Procedure (i think)  for each of the below steps what is the approximate
> time required.
> 
>         1. Basic mix... mix soil and straw with some water ( time required
> approx )

The method here discribed makes batches of appx. 3/4 to one cubic foot each.

Pour all the water in a mix batch into a rotating drum cement mixer, add
1/2 of soil component , then all the sand, and then the other 1/2 of the
soil .
Allow to rotate briefly till mixed & it forms one big lump that falls
off the paddles as the mixer rotates.  Water content is critical as too
mush makes a too soft batch that will stick and hang up inside the
mixer.  Elapsed time per batch 3 to 4 minutes.  Dump directly into a
wheel barrow.

Transport to a tarp & stomp in the straw.  Apply the straw in spread out
amounts just enough to cover the cob evenly.   Stomp in only enough to
embed the straw.  Roll batch into burrito shape &  keep cob mass in
middle of tarp.  Repeat  controlled spread out straw applications 3 or 4
more times on top of the rolled burrito shape & wedge the straw into the
mass starting from one end of the burrito with one person stomping. or
both ends with two stompers.  Observe  mix progress and avoid mindless
energy consuming pointless stomping.  Elapsed time 5 to 10 minutes
depending on stomping efficiency & weight of stompers.  Heavier folks
make better stompers in general.  

Roll into a final burrito shape and pull one side of tarp back over the
batch.  Lay wheel barrow on its side next to the tarp encased burrito. 
Flip covering portion of tarp into the wheelbarrow  & grab other side of
tarp and roll the burrito into the wheelbarrow.  Put one foot on the
wheelbarrow leg & pull the barrow towards you to upright it.  The key to
all this is to think efficient in motion and body mechanics.   Elapsed
time 1 minute

Total time from mixed to wall per batch is around 10 to 15 minutes. 
Ideal crew size is one at mixer & two stomping per tarp.  This crew
should be able to keep 1 to 3 wall cobbers well supplied for constant
building, depending on how efficient they are at building the cob onto
the wall.

..................... 

>         2. From into cobs ( time required approx )

Transport to wall and pull chunks of cob directly out of the wheelbarrow
and put directly in wall.  There is no need to make cobs & all energy
spend doing so is pretty much wasted.  If you need to, as the wall gets
higher, form into balls as you take it out of the wheelbarrow & toss up
to wall builders.  Another approach is to have an easily moveable ramp
so you can wheel the cob in the wheelbarrow right up to the level of
where the wall top is.  This is also more efficient in use of energy. 
Elapsed time depending on technique 1 to 5 minutes per batch.

.....................  
>         3. Apply it to the wall being built ( time required approx )

An efficient building rate using strong hands or cobbers thumbs is about
the same as the above mix rate for two experienced cobbers on the wall. 
Again, think efficient in placing and thumbing,  Do enough to knit the
wall together, but no more.  Some folks don't thumb the cob, but just
put it on the wall & stomp it in place by standing on the wall & hitting
it with a paddle board to keep the wall shape.  This seems it would be
even fasted, but I can't comment to the final built wall quality.
.......................
> 
> Do you only mix enough cob mix that will be used on the given day or
> make enough for several days use.

I've heard of both ways.
Mixer / stomped technique cob seems most efficient as a per day
production rate.
If you are using just tarps and no mixer at all, then doing softer
batches to make the stomping easier & mixing a day ahead of putting on
the wall can speed things up.  This is also true for the mixer cob
described above.
Bobcat or tractor cob where the machine is rented allows / demands
making a huge pile of cob all at one time & then tarping it to keep it
moist and final stomping for quality control as you take it out of the
pile.  I personally have reservations about keeping the straw wet for
too long in such a big batch as it can start to break down, but that's
just opinion at this point.
.....................
> 
> I trying to think of a way to speed up the process.

Yes, this certainly is the key issue to making cob competitive with
mainstream building.  More folks will build with cob when it can be done
more efficiently.  It's sad but true that in our time driven world,
things that are quicker & hence more economical are what wind up
dominating.  A key to remember here is that people in general will take
the easier path and do things in terms of perceived self interest.  When
we make cob that way, then it will begin to happen on a wide scale. 
Until then, it will remain the domain of lovers, madmen and fools.
...................
> 
> One delaying item, I understand is that you can't build up to much on a
> given day and must stop till the next day to continue.

Based on technique, moisture content of the cob and wind / sun
conditions, the build rate can vary from  6" to 18" of wall height per day.

john fordice
TCCP