[Strawbale] Air tightness and earth plastering

Carina Simons carina.simons at gmx...
Thu Apr 21 17:31:17 CEST 2011

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,





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/m?) 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



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