[Strawbale] OSB or Not? (rendering versus sheeting) (dirk witvrouwen)

Michel Van Mulders michelvanmulders at siol...
Mon Dec 6 07:41:35 CET 2010

Hi Jure and others,

This story tells me nothing in favor of OSB.
Max, Tom are presuming that after years, OSB is as much sensitive on moisture as any other natural material.

The question comes back to the basics; too much protection against moisture movement sounds dangerous.

The fact that the plaster started coming off with this man in Austria could as well be of too dry....
A certain amount of moister in the air is necessary to keep natural plaster sound, if there is no binder extra added.

Maybe to be safe in 20 years we should add a binder to the plaster, and make sure that enough breathing is guaranteed... 


The fact is also that earth buildings were "reworked" every few years with a sponge and clayslip to refresh the walls and to close small cracks.

This is in any case a serious matter, and hope to hear more.



On 6 dec 2010, at 06:10, Sport Hotel, Jure Pozar 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.
> Cheers
> Jure
> 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)]
>> Cheers,
>> Max
>> All,
>> 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?
>> Thanks,
>> Dirk
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Michel Van Mulders
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