[Cob] RE: Lorraine's mixes

[Amanda Peck]

Hmmm.  that gray stuff sounds like it might be expansive clay, 
montmorillonite, what they grind up for kitty litter and to soak up oil 
spills.  Worse yet, it might be silt.  I thought I had clay pits up on the 
ridge, from the way it coated cloth.  Nope.  Silt.  It's about the worst 
thing you can build with or on, as far as I can tell.  Well, no, quicksand 
is worse for building on.

Even if it's expansive clay, it's not at all what you'd chose, say to make 
coil pots out of.  Great for waterproofing (and for kitty litter!), but you 
may want the coil pot stuff for cob.

How do both of those work when you try to make them into coils the size of a 
finger?  can, if they're wet enough, bend into fairly small circles without 
cracking?

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

Lorraine wrote (snipped):

... grey subsoil clay which sets like
rock at the first opportunity (and doesn't dissolve without a really
good soak for a number of days)

...........
Your comment about the red clay is interesting.  The clay where the
storeroom is being built is red clay and dissolves almost instantly when
water is added.  I'd tried clays from all around the farm until we were
thoroughly confused as to what we should be using, and rejected the red
clay as being weak.  Perhaps I should try adding a little of it to our
grey rock-like clay and see what results.