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GSBN:Interesting test results
I was just giving a talk for the Engineering Department at Queen's
University in Kingston, Ontario last week. There is a prof/student
team there doing some testing work on bale walls, and I was able to
check out the results of what they've been doing. Very interesting...
They set out to try to determine if they could establish a minimum
strength for a plaster for a load-bearing bale wall. They made a
series of mixes of a 75% lime/25% portland mix, from intentionally
weak to as strong as they could brew it. They then plastered single
bales with these mixes, at three different thicknesses per mix.
Their results indicate that the actual strength of the plaster had
much less effect on the working strength of the plastered bale than
did the thickness of the plaster. So making a really strong plaster
is not as important as putting it on the wall thickly.
They are now busy writing up the results, and will present them in
TLS later this winter, but I thought I'd share this with you for your
Along the same plaster strength lines, this summer I had to send some
test cubes of earthen plaster to a lab for testing before the
engineering firm would let us use earth plaster for a load-bearing
building. Our samples (taken directly from the wheelbarrows of goop
that were going on the wall at the time) came back in the range of
2.1 to 2.4 MPa. This didn't mean much to me until I saw the test
results from the lime/portland mix (taken at 28 days) at Queen's,
where their strongest mix was a 1.7 MPa. I know that a lime-rich
plaster likely takes more than 28 days to reach full strength, but I
was encouraged by the comparison, and the Queen's guys were well
astounded at the earth plaster figures. Especially since the earth
plaster goes onto the wall more thickly than the lime/portland.
Thanks to both of you who've already tackled a Myth/Reality article
for the next issue of TLS. Anybody else?
Chris Magwood / Camel's Back Straw Bale Construction
<a target="_blank" href="http://www.strawhomes.ca">http://www.strawhomes.ca</a>
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