[Cob] cob re wall building problems

[Amanda Peck]

Three things come to mind--one, you've already tried--plastic over the wall, 
although you might try fastening it pretty closely.

two--I would expect pure clay that's been compacted to be almost 
waterproof--hold water long enough between rains to grow a nice crop of 
tadpoles to maturity.  We might have 40-some inches of rain in a year.  My 
"floor test" of sand/clay/woodchips once it dried sat outside in a paint 
roller tray for a year with no visible deterioration.  We did the floor with 
more sand, because it had shrunk quite a bit.  Question--is your mix 
CRACKING--or trying to--given that the straw is holding it together?  It 
doesn't surprise me that it doesn't wet back up to cob stage nicely.

I wonder if the more experienced people on the list think that your 
clay/sand mixture is OK.  Also wonder if some wet sawdust in there might 
slow your drying time down.  DON'T take my word for this, you need the voice 
of experience here!  I'd feel confident in adding sawdust to a floor, but 
would need another opinion on a wall.

Slip--creamy water/clay mix--would probably work better than water for a 
base with which to put the next layer on.  Once again, expert opinion 
welcome.

three:  an acquaintance back in the seventies was a "farmer"--I can't 
remember whether his crop was sprouts or mushrooms, but something that he 
could grow under a roof, not much light.  The problem, he said, was that 
there seemed to be about a three-hour window where the stuff was ready for 
harvest.  Might be time for cobbing parties so that you can take advantage 
of that short window when it's just right to put the next layer on.  Either 
that or do what he did and work more-or-less around the clock, napping in 
the slack times.  He changed professions quite rapidly.



In my part of the country "crusher fines" are called "crusher run."  Other 
areas seem to go with "roadbase."


.............
Mark Thomas writes:

Attempting to build a small cob building on my property south of Deming. The 
cob dries fast in the dry, hot and often windy weather. I have not been able 
to work the next layer into the previous while it is still plastic yet firm 
enough for support. Tried covering with tarps and placing wet hay on the 
wall.


Re-wetting the wall is difficult.  The semi-dried cob does not seem to 
accept water and soften up.   Have tried leaving holes in the top of the 
wall to be filled with water.  Maybe it is the expansive, montmorillinite 
clay?

Any cobbers out here?

Any suggestions?

One good discovery. Crusher fines from the local gravel pit (about 3/8 
minus). Cheap and a good additive to high clay soil that contains lots of 
fine dune sand.

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