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GSBN:Re: French plaster adhesion tests

Thank you André for the added information and clarification. I appreciate hearing about your lab and testing, too. You confirm David Eisenberg's recent information, that playing in the water is an important part of any test.


--On July 21, 2006 6:16:19 PM +0200 André de Bouter forum@... wrote:

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.p";>http://www.lamaisonenpaille.com/Documentation/PDFs/Dossier_Ademe_Paille.p</a>
df Look at page 21 for the adhesion testing.

A metal piece was glued to the 5x5cm pieces of plaster (pr&#xC3;&#xA9;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

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&#xC3;?&#xC2;&#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&#xC3;?&#xC2;&#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&#xC2;&#xB2;
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,




--On July 21, 2006 9:36:04 AM +0200 Andr&#xC3;?&#xC2;&#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&#xC3;?&#xC2;&#xB2; (0,01 MPa) for a lime/hemp (+ a small aount of sand)
> plaster (=25 times the weight of the plaster)
> 8000kg/m&#xC3;?&#xC2;&#xB2; (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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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@...