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Re: GSBN:plaster and straw question
Joergen seems very well qualified and if Lars thinks he should be on the list, that's good enough for me.
Sent: Thu, 24 Aug 2006 7:22 PM
Subject: Re: GSBN:plaster and straw question
Sounds like Joergen would be a good addition to the GSBN list.
on 8.24.2006 6:26 PM, Lars Keller at larskeller@...:
> Dear GSBN...
> Below is a comment from Joergen Munch-Andersen.
> Joergen has been a reliably constructive resource for the development of SBC
> in Denmark all the way.
> I keep passing on the good stuff from GSBN to him, while always thinking
> that he ought to be on the list himself, while at the same time thinking
> that there is no way he'll have the time, but as he has just suggested it
> himself, I would like to suggest that he is invited in ?
> This is what I wrote on this list about him on May 7th:
> ... Joergen Munch-Andersen, whom some of you might have met at
> the ISBBC 04. Joergen is Senior Researcher at the Danish Building Research
> (www.sbi.dk) and has for more than 5 years consistently been constructively
> critical and he has made a huge difference towards making SBC an accepted
> building method in Denmark.
> Furthermore I should say that Joergen has on several occasions shown that he
> is ready to put in time.
>> I believe that what Bruce calls speculation is the way it works. In our
>> report on straw bale building there is a section on experiments with straw
>> bale walls with clay and lime plaster, written in English. Cement is of
>> course more dangerous, but we subjected our wall to very severe moisture
>> conditions for a long time, and still nothing happened with the straw.
>> The report can be found at
>> <a target="_blank" href="http://www.sbi.dk/byggeteknik/konstruktioner/serlige-konstruktioner/halmhuse/">http://www.sbi.dk/byggeteknik/konstruktioner/serlige-konstruktioner/halmhuse/</a>
>> click on download pdf to the right and go to page 46.
>> I cannot quite guess how the wood/plaster walls are constructed,
>> especially where the grade D paper is placed (I assume that it is some sort
>> of a vapour barrier). But if it is on the inside of the wood, rain water
>> penetrating the plaster is trapped between two vapour barriers. If it is on
>> the outside, moisture from the inside is absorbed by to wood. So it is
>> deemed to fail. In a straw wall the mass of the cellulose is much bigger, so
>> it can absorb more water.
>> I hope this can be of help to somebody.
>> JÃ¸rgen Munch-Andersen
>> SBi, Danish Building Research Institute
>> Dr. Neergaardsvej 15
>> DK-2970 HÃ¸rsholm
>> tlf +45 4574 2388
>> fax +45 4586 3575
>> On Jul 2, 2006, at 2:23 PM, Pinyon Engineering wrote:
>>> Hi list
>>> I have been working on revising the Detail Book that CASBA put
>>> together back in 2000
>>> I have a question: Why can we apply cement plaster directly to bales
>>> but not to wood? aren't they both cellous?
>> An ongoing question, subject to lots of discussion over the years.
>> Bob Platts, a very capable engineer in Canada, opened up various
>> cement-plastered bale structures of up to ten years of age (as I
>> recall; it was in The Last Straw a long time ago). He was looking for
>> any sign of problems at the straw-plaster interface, and didn't find
>> any -- no sign of alkaline attack (from the high pH cement), nor any
>> sign of water vapor condensing on the inside of the outer plaster skin
>> (as was widely expected in a heating climate like Canada -- warm moist
>> air moving outwards, dropping in temperature in the wall "cavity"
>> (bale), and hitting the dew point at or near the back of the plaster.
>> There should have been a problem, and there wasn't. Maybe Bob just
>> didn't look hard enough, but, as I said, he's a pretty smart guy.
>> General speculation is that straw, unlike its more dense cousin, wood,
>> is able to disperse any water or condensation by capillarity, then let
>> it dry by any or all of several mechanisms before decay can set in. In
>> a Canadian house in winter, for example, there can be water there for
>> quite a while at the interface, but so long as it remains below 40
>> degrees F or so, the microorganisms don't wake up and start to work.
>> By the time it warms up enough, the water dries up.
>> That is the speculation, anyway.
>> At a wood/plaster interface, the water is trapped, and remains in place
>> as the temperature rises, so the critters start a-molding. I saw
>> abundant evidence of just this behind every failed stucco wall (about
>> 30 of them) that I inspected after the 1989 San Francisco earthquake.
>> Even where there were two layers of grade D paper as per code, water
>> had gotten behind it (the paper) and there was, typically, lots of rot
>> in buildings over ten years old.
>> Bruce King, PE, rotting away the time
>> Director, Ecological Building Network ( www.ecobuildnetwork.org )
>> Publisher, Green Building Press ( www.greenbuildingpress.com )
>> 209 Caledonia St.
>> Sausalito, CA 94965 USA
>> (415) 331-7630
>> bruce@ ecobuildnetwork.org
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