[Strawbale] OSB or Not? (rendering versus sheeting) (dirk witvrouwen)
asbn at baubiologie...
Mon Dec 6 09:55:19 CET 2010
Dear Jure and others...
There are no houses made with strawbales which are older than 11 years in
We have very few houses which are plastered directly on the strawbale (one
of it is my own office). This works very well and the connection between the
wall and the earthplaster is normally better than on wood or OSB with a
plasterground (cement, reed, heraklith...).
So the reason for a falling down earth-plaster is always a bad earth-plaster
with normally too much sand in it (too less glueing binder).
The reason for cracks is always (or most of the time) a plaster-ground with
different materials, e.g. strawbale between wood-posts or two different
boards like gypsum-board and wood (or OSB) or the connection between the
plaster and the wooden window- and door-frames, because natural materials
always have a different extension when the temperature or moisture-content
changes. There is only one solution, to prevent this: a net in the plaster
(earth or lime). Fibreglass is the strongest net to prevent these kinds of
cracks, but natural materials often work well, too.
In one house I saw small cracks on the facade because of the
compression-strings in a loadbearing wall. Again, here are two different
materials (metal strings and strawbale) and there was no net in the plaster
(in this case it was lime).
So OSB does not prevent eart plaster falling down or cracking, OSB has other
advantages (as mentioned). The reason for cracks (after the drying process)
and a bad connection of the plaster to the plaster-ground is always a bad
plaster without a net.
Mit lieben Grüßen
asbn - austrian strawbale network
Österreichisches Netzwerk für Strohballenbau
3720 Ravelsbach, Baierdorf 6
Email: asbn at baubiologie...
> Did the owners maintain the lime plaster with regular lime washes? Are the
> bales actually rotten - all of them? Did it happen gradually or all of a
> sudden after a really bad winter (like last year in Scotland) with wet
> weather followed by freezing weather?
> On 6 December 2010 05:10, Sport Hotel, Jure Pozar <jure.pozar at gmail...>wrote:
>> Dear All,
>> I have in interesting information. I have spoken to a guy who does
>> natural plastering for over 20 years and he said that the houses in
>> Austria which he worked on 20 years ago show problems now. The plaster
>> which was applied directly to the strawbales on the outside is cracking
>> and falling off and they found out because over the years some moisture
>> got inside the straw and made it crumble and dissolve. So the house is
>> no good now and there is no easy way to repair it. I wouldn`t like my
>> house to live the same misfortune in cca 20 years time. This is why
>> vapour barrier and wind proof facade is a good solution. I can`t wait to
>> hear your comments.
>> S, Max Vittrup Jensen piše:
>>> Hi Dirk,
>>> If you'll join the ESBG 2011, you'll see my approach, which I believe is
>>> fairly generic:
>>> Earth plaster straight on vertical bales, sloped ceiling made from beams
>>> with rough wooden boards with about 10 cm spacing to hold the bales
>>> above; the boards covered with reeds below and plastered. (The bales are
>>> also plastered on top, and ventilated below a vapor barrier, which again
>>> is covered with roof tiles, after another ventilation space.
>>> I don't usually consider myself 'conservative', but in this respect I
>>> suppose I am; it's a fairly old proven approach. I'm still waiting to
>>> hear from people who'd gone in and inspected OSB boards after 5-10 years
>>> use above a kitchen (used by a family with children in a country with
>>> plenty of wet and cold days outside). I'd like to see what's hidden
>>> behind the nice plaster below and covered with straw etc. above.
>>> Perhaps it's my simple pragmatic mind, however I can't grasp why the OSB
>>> don't turn black with fungi...
>>> I'm aware of a CZ-Austrian funded project which made such insulations
>>> about 5 years ago, but apart from the architects showing they could do
>>> it (and profiling themselves at conferences and media), then there's
>>> never been a follow up research about the long term effect...
>>> As we also reside in a forested part of Eastern Europe, where rough cut
>>> wooden boards from local forests/mills are still significantly cheaper
>>> (despite the export to Austria!!!), then it makes a lot more economical
>>> sense than OSB.
>>> There's been enough well articulated points about several other
>>> downfalls to OSB, especially from Derryl and Rob Tom, so I'll simply
>>> summarize it with Rob's statement: "OSB Stinks!"
>>> [Which might be why, at the ESBG, you're only likely to find OSB used
>>> for the composting toilets ;o) (We were given some which had been water
>>> damaged in a flood)]
>>> I read people objecting agains using sheet material instead of rendering
>> the bales directly. The reasoning seems to be mainly relating fire
>> protection and sealing air leaks. Yet, lot's of people use bales in their
>> roofs. I'm assuming none of them would render the underside of these bales.
>> So why do it for wall's if it's not done for the roof? Any thoughts?
>>> European strawbale building discussion list
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>> Jure Požar, dipl.org.tur./ general manager
>> HOTEL SPORT& MTB park Notranjska
>> Kolodvorska c. 1, Postojna
>> Tel.: +386 5 720 22 44
>> Fax: +386 5 720 22 40
>> Mobile: + 386 51 630 575
>> e-mail: jure at sport-hotel...
>> skype: jure.pozar
>> Bodi resnicoljuben: nikoli se ne pretvarjaj. Resnica vedno zmaga
>> Be truthful: never pretend. The truth always wins
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