[Strawbale] OSB or Not?

asbn asbn at baubiologie...
Sun Dec 5 14:42:38 CET 2010

Dear Alex

Sure, this is possible. Reed is a good (and one of the oldest) plaster
ground, you just have to fix it well on the OSB (average every 10 cm a
bracket/crib), because OSB has a very plain surface and the plaster doesn't
make a really good connection to OSB by itself.
Mit lieben Grüßen
Herbert Gruber
asbn - austrian strawbale network
Österreichisches Netzwerk für Strohballenbau
3720 Ravelsbach, Baierdorf 6
Email: asbn at baubiologie...

> Dear All,
> I am very thankful for the discovery of this forum. You are truly passionate
> and 
> anybody can learn a lot from all of you.
> I will start building a strawbale house near Bucharest - Romania next year in
> may and as you can see   in the attachment I have osb on the interior for
> structural reason and the easiness of execution. My question is: It is
> possible 
> or NOT to plaster OSB with lime mortar on reed blanket? Anybody do that? Any
> tips and tricks? 
> Respectfully yours,
> Alex Cristescu  
> ________________________________
> From: asbn <asbn at baubiologie...>
> To: European strawbale building discussions <strawbale at amper....muni.cz>
> Sent: Wed, December 1, 2010 11:08:13 PM
> Subject: Re: [Strawbale] OSB or Not?
> Dear Michel, Jure and...
> Why do you compare a (thick) layer of earth/clay directly affiched/sprayed
> on strawbales with a (thin) layer of earth/clay on OSB?
> If this plaster has the same thickness, the thermal mass is the same.
> Let me try to explain, why OSB (or diagonal bracing with wood) is used:
> a) for the structural strength of the wall, which has to be guaranteed (and
> is much easier to calculate with the infill-system), otherwise your house
> would not withstand the windforces and snowloads. You can make diagonal
> bracing with metal (which is always a problem because of a possible
> corrosion) or with a structural wood(board) or you can rely on the
> structural quality of the sandwich-system earth-straw-earth(or lime). But I
> would not want to explain or proof this to a building official...
> b) second you need an airproof layer on the inside and a windproof layer on
> the outside of the wall, especially if you want to build a low-energy or a
> passive-house. These layers can be folies under the plaster (which are ­ as
> OSB ­ nearly impossible to plaster directly without cement) or OSB - this is
> the great advantage of the OSB-board: it functions as structural board AND
> airproof layer (Dampfbremse) on the inside of the wall. Airproof in this
> case means: it guarantees, that your (strawbale) insulation has the full
> thermal quality and it reduces the moisture going in the wall (from inside).
> We never plaster OSB directly, we use an installation-layer like 3,5 ­ 5 cm
> Heraklith-BM (magnesite-bound), which is similar to Fibralith
> (cement-bound). This board is an ideal plaster-ground and somewhere you have
> to put all your installation (heating, water, power) in the wall. Some do
> that in the straw (I never would do that), some say, they can do it just in
> separation-walls or floors. I don't believe that.
> So, this is the reason, why we have these layers: every layer has a function
> to guarantee the structural (wind, loads), physical (moisture) and thermal
> (full insulation capacity) of the wall.
> You can change the materials (like OSB), but you have to find a material,
> which has the same qualities.
> I looked long for a subsitution for OSB (in a time, when OSB was not
> available formaldehyde-free), but only found MgO-boards in China, which have
> the same quality (but are too expansive if you add the transport).
> Yes we built with diagonal wood-bracing, folies, reed or Heraklith-BM (as
> plaster-ground) and earth-plaster in the beginning, but if you calculate the
> price of the materials AND the work, OSB is much cheaper.
> We want to build ecological houses in the best possible (ecological and
> structural) quality to the smallest possible price, this is why we have
> choosen OSB and Heraklith-BM and strawboards (the Czech ecopanely) as
> separation-walls...
> This is - im my opinion - important, if you build for and sell a house to a
> customer, if you do it for yourself, you can do all these experiments,
> because you are not capable and can plaster cracks as often as you want.
> But if you build a house as a carpenter or professional strawbuilder for
> money, you have to be more careful, otherwise your company will not last
> very long...
> Mit lieben Grüßen
> Herbert Gruber

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