[Strawbale] the BIG question

Wed May 10 20:37:46 CEST 2006

Hi Michael,

The original qoute I responded to said failures reported in NE America. I 
didnt say all buildings in America were ciment rendered, just my observation 
that  quite a few have been, especially in cold snowy areas like the NE.

A stucco plaster is called stucco because it contains either lime sand mix 
which is the original method or the modern ciment/sand mix, in the UK called 
a render. Gypsum based plasters are called plasters not stucco.

I understand that in drier areas like Arazona, clay or lime based plasters 
are used, in colder, wetter areas ciment/lime finishs are more ususally 
used.

It is a shame that there does aopear to be a tendancy to try and ignore 
problems/failures in in case the "cause" is damaged. I think there is a 
tendency to panic at the eleventh hour and put on a ciment based finish.

>From: "Michael lough" <michaelklough at sympatico...>
>Reply-To: mkl18 at pobox...,        European strawbale building 
>discussions<strawbale at amper....muni.cz>
>To: strawbale at amper....muni.cz
>Subject: [Strawbale] the BIG question
>Date: Wed, 10 May 2006 04:48:42 +0000
>
>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 at sympatico...>
>Reply-To: mkl18 at pobox...,        European strawbale building 
>discussions<strawbale at amper....muni.cz>
>To: strawbale at 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 at btinternet...>
>Reply To: European strawbale building discussions 
><strawbale at amper....muni.cz>
>To: "European strawbale building discussions" <strawbale at 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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>____________________________________________________
>    European strawbale building discussion list
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>Send all messages to:
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