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[Strawbale] the BIG question
sorry for lateness in replying but have been distracted recently?
"There have been reports of "failed" straw walls in NE America with some
admitting the damage was likely caused by dampness but no admission of the
dampness being caused by convection currents within a wall, therefore no
remediation has been undertaken as it has not been proved. Which of course
means here "business as usual"
+++I wonder how many of these failed walls were plastered with a cement
based render/stucco?
I know the Americans like their straw bale buildings cement stuccoed.
A generalisation I'm afraid. It is true that Portland/Lime mixes are used
and one Strawbale commercial group in Canada has even accepted web
"sponsorship" from a Portland cement manufacturer but Portland use in
plaster is not the case all over North America. In the US there are quite a
lot of Lime/sand plastered structures I believe. The heritage of straw bale
appears to me at least to be more Arts/craft conscious less "industrial"
than in Canada.
The issue of Portland containing plasters (not stucco, that is gypsum based
I believe) and the effect it may create once on straw over time in a humid
region is one I am not that informed on. But it appears that the test of
time is underway. One hears of problems and discussion and then nothing?No
resolution, no rockingthe boat. Time perhaps unfortunately will tell?But
then again I may be "outside" the truth. There is doubt here in quiet
corners.
The real problem is the cost of real industrial testing of straw bales.
++I think if you are going to use an organic material in a buildings
structure, provision for air movement through that structure becomes
paramount, even at the loss of thermal performance.
It depends on the amount of the moisture in the air and at what point does
this warmed moist air come into contact with outside conditions which will
then turn the moisture back into water? This is the question. The dew point
can move with the seasons also.
What could happen if say heat went into plaster from the inside which warms
the air immediately inside the bale Will this heat rise through the bale(s)
If there is air inside the bales why wouldnt it? And would this air form a
convection current inside the bales albeit a slow one. If the outside is
cold then the warm air would meet the colder outer bale inside surface at
some point and condensation would result ?? Would Portland allow for
"expiration"? Doubtful as it is used for swimming pools?
++"sealing" in a straw bale wall with cement plaster seams like asking for
trouble unless it is a dry climate.
I share your instincts.Many others do as well. In Canada the potential for
problems is not seemingly acknowledged by everyone .
It would be interesting and very useful to have a reference to straw bale
wall "failures" to learn from, is anyone making a comprehensive record of
these situations?
let it move, let it breathe!
The single most important problem of building with straw bales is not the
subject of a permanent record. (not one that I have seen anyway)
It seems as though the collective attitude is to not give straw bale
construction a bad name while these problems are discussed quietly. The
trouble is that there are some perhaps less scrupulous individuals that
believe that no apparent discussion means no problems which means using
Portland is OK.
its all a bit disturbing ?
regards
Michael
From: "Michael lough" <michaelklough@sympatico...>
Reply-To: mkl18@pobox..., European strawbale building
discussions<strawbale@amper....muni.cz>
To: strawbale@amper....muni.cz
Subject: [Strawbale] convection currents within a straw bale wall?
Date: Wed, 03 May 2006 13:07:49 +0000
Mark said?
There is a disparity between directly-measured U-values for strawbale walls
and U-values calculated from measured thermal conductivity of bale samples;
the best explanation anyone has been able to give for this is slow
convection currents in - or rather around the outside of - the bale wall.
The disparity was worst in the case of the least professionally plastered
test in the US. I would therefore expect the thermal performance of a
system which uses cladding _instead of_ external render to be substandard.
This seems akin to the "theory " that there is the possibility of moisture
produced within a bale wall being part of the convection current. And this
being condensed at the top to moisten the outside top wall and in worst case
scenarios (presumably in more humid climates) maintain a permananent risen
damp within the straw bale wall which could if not in a few months probably
over years produce the conditions for microbial activity ??
I understand someone called Jenik is active with unfunded experiments in
Europe to test various methods of stopping this moisture transfer. Do we
assume by his activity and your acknowledgement of a concensus on the
probability of convection currents in a straw bale wall that there is room
for concern in parts of the world where humidity is a factor such as
Northern Europe and parts of North America? There have been reports of
"failed" straw walls in NE America with some admitting the damage was
likely caused by dampness but no admission of the dampness being caused by
convection currents within a wall, therefore no remediation has been
undertaken as it has not been proved. Which of course means here "business
as usual".
Care to comment?
Thankyou
Michael Lough
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____________________________________________________
From: Oliver <obswann@btinternet...>
Reply To: European strawbale building discussions
<strawbale@amper....muni.cz>
To: "European strawbale building discussions" <strawbale@amper....muni.cz>
Subject: [Strawbale] Tadelakt on strawbale
Sent: May 3, 2006 10:53:20 PM
Hi,
Does anyone have any experience of tadelakt on strawbale? Is there anyone
out there who could run a tadelakt workshop in Scotland.
There are a variety of volunteer opportunities on www.naturalhomes.org. If
you would like to post your workshop on naturalhomes.org to attract
volunteer workers please send me details.
Regards,
Oliver
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