[Strawbale] Air tightness and earth plastering

Thu Apr 21 22:58:50 CEST 2011

Thanks Seb. One example that I think will tell you more about the blower
test result is a house in Ottawa that I worked on. We did a house and a
separate workshop. The house was completely plastered (interior with finish
coat) and exterior (I guess this is what we are now calling render) with
finish coat. The workshop had nothing on the straw interior and only a
scratch coat on the exterior. Even though both buildings were on the same
heating systems, each specifically designed for the space they heated, the
workshop would NEVER warm up whereas the house was warm right away. Now that
the render/plaster is complete on the workshop, it is heated perfectly.
That's how big a difference the lime (in this case) made.

Andrew

On Thu, Apr 21, 2011 at 1:44 PM, Sebastien Hubert <
sebastien.hubert at mc2000...> wrote:

>  hello,
>
> As I'm not english native speaker I probably made a mistake...  I thought
> render means the last finished earth layer...  It seems this is not the
> case...
>
> Thus to summarize, in our building the earth plastering is done but we
> still need to do the last finish layer...  At the moment we have more or
> less 5cm earth on the straw bale walls.
>
> Regarding the first house where they made the blower door test, on the
> basement walls they only put 1.5cm earth plastering and the finish layer is
> not done yet...
>
> I hope this is clearer now ;-))
>
> Thx
>
> Seb
>
>
>
> On 21/04/2011 18:34, paul paul wrote:
>
>
> To try and answer your question Carina, it looks like they use the word
> “render” to mean interior undercoat, before a top or finish coat of plaster
> is applied. In this case, an undercoat of plaster was not applied first,
> which is why the total thickness of applied plaster was quite thin. As I
> said in my first post , sometimes an interior undercoat is called a
> “render”, possibly because quite often the undercoat would be cement/lime
> based, like an exterior render, and then finished with a gypsum plaster top
> coat.
>
> Paul
>  *From:* Carina Simons <carina.simons at gmx...>
> *Sent:* Thursday, April 21, 2011 6:29 PM
> *To:* 'European strawbale building discussions'<strawbale at amper....muni.cz>
> *Subject:* Re: [Strawbale] Air tightness and earth plastering
>
>
> Hallo,
>
> If render and plaster is he same, than what is meant with the problem of
> the air tightness in the passive house. There was said that the air
> tightness was not so good because of the failing render but then earth
> plaster was on it!
>
>
>
> Greetings,
>
>
>
> Carina
>
>
>  ------------------------------
>
> *Von:* strawbale-bounces at amper....muni.cz [
> mailto:strawbale-bounces at amper....muni.cz<strawbale-bounces at amper....muni.cz>]
> *Im Auftrag von *Andrew Morrison
> *Gesendet:* Donnerstag, 21. April 2011 17:46
> *An:* European strawbale building discussions
> *Betreff:* Re: [Strawbale] Air tightness and earth plastering
>
>
>
> As far as I know, they are the same. Here in the United States we say
> plaster. When I was in Australia teaching last month, they spoke of render.
> I don't know of a difference.
>
> Andrew
>
> 2011/4/21 Carina Simons <carina.simons at gmx...>
>
> Hallo to everybody,
>
>
>
> Since I am not a native English speaker I do not know the differents
> between a render and a plaster. Can anyone explain that to me?
>
>
>
> Many greetings,
>
>
>
> Carina
>
>
>  ------------------------------
>
> *Von:* strawbale-bounces at amper....muni.cz [mailto:
> strawbale-bounces at amper....muni.cz] *Im Auftrag von *Sebastien Hubert
> *Gesendet:* Mittwoch, 20. April 2011 22:53
> *An:* strawbale at amper....muni.cz
> *Betreff:* [Strawbale] Air tightness and earth plastering
>
>
>
> Hello everybody,
>
> Till yesterday I was pretty confident that it was possible to make a good
> air tightness using earth plastering.  Yesterday an other professional
> called me regarding air tightness.  His neighbor and him did a blowerdoor
> test to verify the airtightness of their 2 passive houses (should be
> passive).  The result was not good.  The n50 leakage rate is supposed to
> be smaller than 0.6. The building must not leak more air than 0.6 times the
> house volume per hour (n50 ≤ 0.6 / hour) at 50Pa (N/m²) as tested by a
> blower door.
>
> He obtained n50 = 1.2 and it was 0.95 for the second one.  They worked 2
> days trying to find what could be the problem and didn't find any major
> leakage.  There was 1 point that could be a problem.  A basement wall that
> is part of the living space get only 1 layer of earth plastering but no
> render.  The thickness is more or less 1.5cm.  They decided to glue a
> airtightness sheet (1 square meter) on this wall.  They blew the air outside
> of the building.  Then they saw the sheet (that has been glued) inflating
> meaning that the earth plastering was not airtight.
>
> Of course, I have to say that it would be better to put the render on this
> wall.  Airtightness should be probably better.
>
> I'm building a straw bale (this is our house) and we really want a good
> airtightness.  For the wall, the earth plastering is supposed to do the
> airtightness.  We are going to make a blower door test before finishing the
> details.  This means the renders are not ready yet because we will put the
> last earth layer on the wall and ceiling at the same moment.  This will be
> done after the blowerdoor test.  This means that the blower door test will
> perhaps not be successful.
>
> What do you think about it ?
>
> Does anybody already make a blowerdoor test with earth plastering
> airtightness ?
>
> I would really appreciate a feedback.
>
> Many thanks
>
> Cheers
>
> Sebastien
>
>
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> --
> Andrew Morrison
> Consultant, Teacher, Inspiring Change
>
> ===================================================
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>  ------------------------------
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> ____________________________________________________
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> ____________________________________________________
>     European strawbale building discussion list
>
> Send all messages to:Strawbale at amper....muni.cz
>
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> ____________________________________________________
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>
>
> ____________________________________________________
>    European strawbale building discussion list
>
> Send all messages to:
> Strawbale at amper....muni.cz
>
> Archives, subscription options, etc:
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-- 
Andrew Morrison
Consultant, Teacher, Inspiring Change

===================================================
Learn the Secrets to Successful Home Construction:
www.BeYourOwnContractorTraining.com<http://www.beyourowncontractortraining.com/>
===================================================
Get Your Straw Bale Construction Questions Answered at:
www.StrawBale.com <http://www.strawbale.com/>
====================================================
Sign Up For a Seven Day Straw Bale Construction Workshop Near You at:
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====================================================
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