Re: GBlist: re: Natural Sealants

Marc J. Rosenbaum (Marc.J.Rosenbaum@valley.net)
23 Feb 97 21:15:11 EST

Rob --- You wrote:
I'll bet that there're a bunch of Natural Building Nerds (NBN) wondering
about the manner in which the straw-clay walls failed.
Care to 'splain it to us ?
--- end of quoted material ---
Great question, Rob. I have to admit I wasn't there to examine the straw-clay
walls in detail. But... It seems that the builders, trained by Robert LaPorte,
indeed, they hail from Iowa as well, used silt instead of clay, or at least
silt was a significant component of the mix. The symptoms include:
* incredibly slow to dry - my guess is that this may be to silt's phenomenal
affinity for moisture
* lots of shrinkage - there are horizontal wooden reinforcing/stabilizing poles
in the walls, and there is a significant crack beneath each of these, where the
straw-clay has settled.
* they seem more brittle and less strong to me in a cursory examination than
the small section of wall a number of us built in a workshop with Robert at
this site in the summer of 1995. This workshop wall used bagged clay.

My own experience post-workshop was not great, either. I went to a local pit
and harvested a pick-up truck load, about 1200 pounds, of what looked like
beautiful clay. I did the settling test and the results were well within what
Robert's booklet (MoosePrints) says is required. Neverthe less, when I finally
mixed up my clay slip, and mixed it with my straw, I couldn't get any
reasonable amount of adhesive strength from the clay. A local potter I had
designed a home for years ago came by to look at it, and he said there was a
trace amount of sand. He advised me to get some ball clay. I got 5 pounds of
ball clay and it worked great. But I decided that, based on some back of the
envelope calcs, that the 600-800 pounds of ball clay that I needed for a 3 wall
8x12 room didn't seem very "sustainable" if it had to come from KY or TN.

As to your suggestion about very light gauge, Larsen truss-like studs for the
infill walls - my concern was movement in the framing causing cracks in the mud
plaster that will be used to finish both sides of the walls. My experience
with 2x2s is that they move around quite a bit. And I am guessing that the OSB
will be a no go with the owner, although presumably the fiberboard which has
already passed muster could be used for the gussets. Apparently the fiberboard
makes an OK base for the plaster, because they've already used it with no
problems (I'd have been nervous about expansion/contraction of the fiberboard
leading to cracks.)

The gaskets are a good idea, Rob, and I think that this one MAY sneak by the
owner, since it appeared that some type of bulb weatherstripping was used on
the site-built windows.

Once I get a look at the top plate area, I'm guessing that gaskets may be the
solution (although this area just begs for a foam gun!)

Thanks for your thoughts.

Marc
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