[Strawbale] Air tightness and earth plastering

[paul paul]

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 
Sent: Thursday, April 21, 2011 6:29 PM
To: 'European strawbale building discussions' 
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

 


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Von: strawbale-bounces at amper....muni.cz [mailto: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

 


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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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