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Re: GSBN:Clay plastered wall passes 1-hour test!



Hello Derrek,

> If I understand the numbers, adding some hemp to the lime plaster
> _decreases_ adhesion by a factor of eight.  That's a big surprise to me.
> Can you tell us more?  How was the testing done?  I'm guessing that these
> are shear-strength values.  Is that correct?

I was not part of the testing. I can only try to translate the info from the
french report (wich also reports on fire testing and breathabilaty of the
plasters):
<a  target="_blank" href="http://www.lamaisonenpaille.com/Documentation/PDFs/Dossier_Ademe_Paille.pdf";>http://www.lamaisonenpaille.com/Documentation/PDFs/Dossier_Ademe_Paille.pdf</a>
Look at page 21 for the adhesion testing.


A metal piece was glued to the 5x5cm pieces of plaster (pr?cut on the surface of
a sb wall with a rotating blade) which were then tore off the SB wall.
In most cases (if I understand correctly) some or most of the plaster stayed on
the wall. The glue taking of only a layer of the plaster.

I agree with your observation that the lime/hemp mix was more fragile. But don't
forget that the french lime/hemp mix is normally used for insulation and has a
very high dose of hemp and just 'a pinch' of sand. I have know idea on what was
used for these tests.

> I'm also curious about how thick the tested plaster was.
I believe both type of plasters were 2 cm thick (that is a thickness I see
mentioned elsewhere during the testing. It is not specificly mentioned for the
adhesion test.

Andr&#xCC;&#xA9; mentions
> that that the adhesion strength figures are equivalent to 25 and 200 times
> the weight of the plaster.  I'm thinking that increasing the thickness of
> the plaster on a bale wall would have little effect on adhesion, but a
> major effect on plaster weight per square meter.  Andr&#xCC;&#xA9;, please tell us
> more about how the strength per weight of plaster is calculated.
I haven't a clue. All this calculation stuff is way over my blond little head.
That's why I'm so glad that guys like mr King and moosehugger Rob Tom are part
of this clan.

Hope this info helped.

Samuel Courgey is the SB guy who is responsable for the testing. But his problem
is lack of time and English... I'll ask him if he plans to come to Canada.

In my own lab (a plastic tarp pulled over metal arches) we did some very basic
testing of our own during a workshop: 2 small pieces of wood (4cm&#xD3; each) were
incorporated in a 50:50 straw/earth mix. You guessed it: one on the each side
of a bale. We then tried to pull them out by hanging a big bucket from them (a
piece of plastic wire came out of the plaster). The bucket was was slowly
filled with water. The first test was impressive for us newbie testers; 40 kg
did not get them out. The next day I went swimming with some of the workshop
participants (yes, What a life!) while others got back to testing. At 80kg the
piece of wood was pulled out of the small side of the bale (the plaster side
when the bale is layed flat). The other one did not bulge at 80 kg. The left
over testers called it a day and went to have a shower.
While discussing the results we realised that rather than testing the adhesion
we had tested the cohesion(?) of the plaster as we had not thought of cutting
little 5x5 cm pieces. Anyhow, all workshop participants were impressed and went
home feeling that plaster will stick to both sides of the bale!

Now sorry to repeat myself, but do we have more sientific testing that compares
sb layed flat with bales on edge?

Bale and plaster on,

Andr?



Bye

>
> Derek
>
> --On July 21, 2006 9:36:04 AM +0200 Andr&#xCC;&#xA9; de Bouter
> forum@... wrote:
>
> > Sorry, there was a mistake in the info I shared on French testing.
> > this is the right info:
> >
> > Plaster on bales layed flat:
> > 1000kg/m&#xE5;&#xD3; (0,01 MPa) for a lime/hemp (+ a small aount of sand)
> > plaster (=25 times the weight of the plaster)
> >
> > 8000kg/m&#xE5;&#xD3; (0,08 MPa) for a lime/SAND (no hemp)plaster (=200 times the
> > weight of the plaster)
>
>
> Derek Roff
> Language Learning Center
> Ortega Hall 129, MSC03-2100
> University of New Mexico
> Albuquerque, NM 87131-0001
> 505/277-7368, fax 505/277-3885
> Internet: derek@...
>
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