Re: SB: skins of earth and cement

["Huff 'n' Puff Constructions" <huffnpuff@shoal.net.au>]

G ' day Balers

I would like to add my two bobs worth here in defence of
earthen renders.  First I would like to explain that what I
am about to say applies to small load bearing straw bale
buildings around 90 sq. metres or less.  We now have five
small buildings up in Ganmain as part of our home.  Two are
now fully rendered and in the case of Jack's Flat has been
finished for over 12 months.

The Marriage Room is only just complete with one more
interior coat of white clay.  Just as a revision we have
used Ganmain earth/Golden Canmain Chaff/Sand as the mix for
the first three coats finished to 50mm or 2".  We allow
these three coats to dry completely and then for the
exterior we apply two coats of lime putty and sand to a
depth of 20mm or 3/4 of am inch a total thickness of 70mm.

All the buildings are load bearing, no netting, no pinning
or rebar and no sewing.  We rely totally on high tensile
fencing wire and medium gripples for pre-compression and tie
downs.  (This system we tested to 60metres /second with a
cemnet render.) So far we have a hand full of small vertical
cracks in one wall and that has occurred 12 months since it
was finished.  The walls have settled where I span was a wee
bit too far apart for the weight of the walls.  Other than
that the walls are behaving extremely well and I have no
hesitation in recommending this method as a low cost
sustainable building technique.

Mike Faine from the University of Western Sydney will soon
be starting a series of load bearing tests using Ganmain
earth and Chaff.  We are looking forward to the results and
I hope that the laboratory tests will prove the field
tests.  So do not be in fear of earth and straw being strong
enough to hold up your roof as long as the design suits and
is small with small bales then just do it.  If you are game
to use the jumbo bales say a 2.4m x .900mm x .600mm for a
load bearing house you will definately have no worries with
strength with or without render.

Sergio Zori Architect Wrote:

 "Vapor transmission rates. If vapor transmission rate of
earth plaster is greater than vapor transmission rate of
stucco exterior, then the earth plaster could only be used
on interior if it is finished with a clear vapor barrier
material. Otherwise, you run the risk of moisture collecting
in the SB and causing mold/mildue and SB deterioration.  If
vapor transmission rate of earth plaster is equal to or less
than that of stucco exterior, then OK, as long as skin
structural strength is approved."

We would need to do some work on this or has enough work
been done.  It is an interesting area to look at but my gut
feel says that earth and chaff or sawdust with a lime putty
finish should perform very well in dealing with moisture.
So far all is going well with our renders and the bales are
very dry and as fresh as the day they went in.  We live in a
24" rainfall area.  Hot summers and cool mild winters.  So
time will tell but I would rather have an earthen render
than cement stucco, just a gut feel.

Kind regards The Straw Wolf.
http://strawbale.archinet.com.au
61 2 6927 6027



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