[Cob] question re using1. Lime 2.Formwork 3.pine chips 4 supportfor walls

[Amanda Peck]

Hi Lori.

It sounds rather a though it's time for you to look at a book. Evans, Smiley 
et al for sweeping you along, and scope, plenty information as well.  I 
think people are slightly more apt to have Becky Bee's out with them on the 
job-site.

1.  There may be some other reasons, but lime would be very rough on bare 
feet if you tried to stomp it.  I've cracked the skin my hands finishing 
(lime-containing) concrete without gloves.  I suspect that it doesn't do a 
lot of good inside the wall--as an outside plaster, yes.  But there are 
people here who have a lot more experience with it than I do.

2.  Centuries old cob houses did have reasonably straight walls.  I seem to 
remember reading that some of them were done with forms, maybe thicker walls 
than are currently used.  It's easier and possibly stronger to do straight 
walls with straw bales, then put cob details on it.  Becky Bee has pretty 
precise instructions on how to make flat, slightly tapered walls.  
(Skyscrapers and most stone walls have tapered walls)

3.   Wood chips ARE used in a cob-like mixture.  They don't have the tensile 
strength that straw adds.  They ARE commonly used in forms, or as plaster on 
a wattle and daub structure--as fill for a post-and-beam wall.  They are 
thinner and lighter than the massive cob wall but still with some of the 
humidity tempering properties that cob walls have.  I'm considering "light 
clay" (as either this or a clay slip tossed with straw and stuffed in forms 
is called) for interior walls.  Not as dense, more insulation.

Rob Roy, talking about mortar for his cord-wood masonry building, says that 
he much prefers pine sawdust as an additive to his concrete-containing 
mortar.  Apparently there's a conflict between the sugar in the hardwoods 
and the concrete.  So, yes.  I used pine chips in my floor (no lime) because 
I already had them from chinking the walls of the cabin (which I have to 
redo, durn it--either the logs continued to shrink, or I didn't have enough 
sand in the chinking--both are probable)

4.  I think that this is a couple of questions.  The walls are going to be 
stronger if they are curved and buttressed.  You DO need a plate on top to 
spread the load for your rafters.  There's been a recent thread here that 
suggested that reinforcing bar (re-bar in the U.S.) is not only a nuisance 
but worthless in cob.  Weren't OLD half-timbered walls cob- or some kind of 
light clay-filled?
........................
Lori wrote (snipped a bit):

1.	Can anyone tell me if lime can be used in a cob mix, or is it
only used when no straw is used with the earth?  If not, why not,
please?
2.	My husband is concerned about getting walls straight and intends
using flat metal formwork.  Is this still considered cob, as the mix is
likely to get pushed/poured/pressed into the molds, or would it then be
a type of rammed earth? Would it then need the hard ramming that is
given to rammed earth?
3.	We have heard that in some parts of Germany cob is made with
wood chips instead of straw.  Has anyone any practical experience of
this and the advantages or disadvantages?  We have access to plenty of
pine chips and pine shreds. Would pine wood be OK?
4.	Using cob, can the walls be monolithic, or do they need supports
of some kind to give them strength?

I look forward to your helpful comments.

Sincerely,

Lori