[Strawbale] moisture

Derek Roff derek at unm...
Fri Apr 8 19:43:05 CEST 2011

I agree with Andrew, that the relative permeability of the interior and 
exterior plasters is an important consideration in very damp situations 
like saunas and bathrooms.  I'd like to add that very careful 
construction detailing is probably even more important.  Research by 
the Canadian Mortgage and Housing Corporation (CMHC), an agency of the 
Canadian government, showed that having a continuous air barrier was 
very necessary to avoid moisture problems within the walls, regardless 
of construction method.

Tiny cracks, holes, and seams that allow air movement into the walls 
will transport a lot of moisture with them; that moisture will be 
concentrated at a few spots, and condensation within the wall is very 
likely.  This can easily cause mold and other microbial bale decay.  A 
small break in the air barrier may transport more moisture into the 
wall than the diffusion through several square meters of plaster.

Build carefully, and if possible, check for air gaps and leaks before 
putting the sauna or bathroom into service.


Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek at unm...

--On Friday, April 8, 2011 10:02 AM -0700 Andrew Morrison 
<Andrew at StrawBale...> wrote:
Hi Niki and Jonas. I would be careful using a material like clay 
(earthen plaster) on an interior surface and lime on the exterior. Keep 
in mind that clay allows for more movement of vapor (is more 
"breathable") than lime. This means that one can transport say 1 
measure of vapor into a bale wall through the clay plaster while only 
allowing for .75 measure to move out through the lime in the same time 
period. This means that excess moisture can get stuck in the bales.

I have a wet sauna here in the states made of straw bale walls. I used 
lime plaster on both sides of the walls with a lime paint on the 
interior. After a sauna is completed, we open all of the ventilation 
ports and through an extra log or two into the fire. This drives the 
moisture through the vents and walls and dries things out with the dry 
heat of the fire. It's very successful.


On Wed, Apr 6, 2011 at 8:46 AM, jonas kacerauskas 
<jonaskacerauskas at gmail...> wrote:

Hello Nikolay,
Here in Lithuania 4 years ago we have built straw bale bathhouse (like 
sauna, just with a lot of moisture - we call it russian sauna), where 
we use simple clay plaster about 3 cm. on interior wall and from 
the incident water protect with wooden plankets (there is natural 
ventilation inside). On exterior we did lime plaster - till now 
everything works fine. tadelact is quite expensive way and not needed 
way to deal with it. As we saw its enougth just clay plaster to deal 
with humidity and ussual you need to protect just several places from 
the direct water and were are a lot of ways to do it:)
best regards

2011/4/6 Nikolay Marinov <nikvesmar at gmail...>

Hi everyone,
I would like to ask you for advice and share your experience about 
preventing moisture, penetrating into SB walls from bathroom, and other 
spaces with high humidity level.
What kind of layers and finishes do you prefer to protect your wall if 
not using conventional waterproof materials.
I know few techniques as: Tadelakt (good water barrier but time 
consuming); Double skin wall with ventilated space between,glass on the 
wall, but it would be nice to share a trusted and working in time 
method that builders and designers like you prefer as solution.

Thank you in advance for you opinion.

Have a nice spring sun.

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