Cob: light clay infill question

[Shae Tebbetts]

Hi all,

We finally bought our land.  I looked up our states geological maps to find 
the best land for cob building that was closest to dh place of employment.  
It is a 6 acre hill full of sandstone, slate and clay with a creek at the 
bottom.  We had been living in a tent since May 2002, with plans of building 
a small cob room the first year and then building onto that the following 
years.  Anyway, to make a long story short, our military tent along with all 
our household items burned to the ground due to our own carelessness (makes 
me sick to think about).  So we had to move in with our inlaws since we have 
2 children.  That has changed plans a lot.  Now we need a home quick!  So 
we've started building a stick frame cabin.  It will be small, yet all the 
space we need to give us plenty of time to build the cob house.

My concern is that I don't want us to sink a lot of money into this cabin.  
The foundation is sortof a pier system with the floor off the ground.  My 
father in law got involved in this, so alot of this has been his ideas up 
until now since he's helping us financially, etc. etc.

Well my question is this:  I want to use light clay straw to fill the 
traditional stud walls.  My understanding is that light clay straw is 
typically setting on the ground or a stem wall.  My concern is will the 
floor,.which is suspended off the ground with piers, be able to bear the 
weight of the light clay wall infill.  We won't have an inner or outer 
sheathing, but rather cob plaster in and out.  I'm thinking it would 
probably work if the light clay walls are only 3.5" thick because we have 
been overbuilding a bit so far...piers are every 3.5-4 feet.  The beams 
(under the joists? are 2"x8"s and they are every 3.5 feet.  Then the joists 
are 2"x8"s and they are on 16" centers.  I have no idea of how to do the 
calculations to see if this will work.  I think light clay straw is 30-50 lb 
per sf depending on the quality of clay.  Lath may be necessary, but I'm 
hoping we can get around it somehow.  I was thinking that we could always 
add a retaining wall later for additional support using all the really great 
stones we have.

I need some input as to whether anyone thinks the floor will be able to 
carry this load or not.  If so, should we just stick with 3.5" or how thick 
of a wall do you think we can get by with?

Thanks,
shae




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