[Strawbale]RE: strawmud sauna

Rene Dalmeijer rene.dalmeijer at hetnet...
Sat Jul 24 19:47:57 CEST 2004


I replied off list to Rikkert and Joost in Dutch. But now realise seeing 
your remarks that I should have done so on-list.

I completely support you in your remark that avoiding moisture problems is 
the main issue in a SB sauna. This is in the case you insist on using SB 
for the building. My question though depends on whether the object of the 
exercise is to make a SB building or a sauna. I suppose in the case of 
Rikkert he wants to build a SB building and a sauna might be a good use for 
it. If this is the case using a radiant reflective surface on the inside as 
you and I both suggested is the way to go. My reason for not suggesting 
wood is that I expect it will require much more work then the (transparent 
corrugated plastic).

Coming back to the practicality of using SB for a sauna. These are my 
considerations. Basically a sauna should be easy to bring to a high 
temperature quickly and not have hot and cold spots which will feel 
uncomfortable. Specifically this means that the interior surfaces should 
not be much below air temperature when in use. A structure exhibiting good 
radiation insulation and a low thermal mass would be the most suitable for 
use as a sauna. This means that the general practice of a wooden, 
relatively lightly insulated, out building is not a bad idea for a sauna.

Although I must say that I like the challenge of making a workable SB sauna 
specifically for our cold and sometimes moist climate. As you say if we 
could make a workable SB sauna then surely we have proved a point.

Below is the essence of my earlier reply to Rikkert, Joost and additionally 
a reply to your mail.

Once you place the wooden interior boarding or other radiant heat reflector 
the mass of the plaster becomes irrelevant. The wooden shuttering will 
reduce the radiation losses to the plaster mass to such an extent that you 
will not notice its presence. I suggest you do use a full layer of plaster 
as it is a serious and important precaution in safeguarding the hay bales 
against moisture damage. The thicker plaster will be able to buffer the 
moisture and allow it to be released when ventilated.

Structurally it is also necessary for a LB SB wall to have both faces 
plastered otherwise the walls will be prone to bowing out to the side with 
thick plaster.

A curved wall will markedly improve the performance in this respect but is 
not a complete insurance. I have recently seen a small round LB SB building 
coated with earth plaster that was very lopsided and very close to being 
given up as a safe structure. Most probably the main reason for the 
instability of this building was the fact that the door opening had created 
a flexure point in the structure. ie the door frame should have been a 
sturdy box with braced corners thus completing the circle. This was not the 
case in this building.

At 07:36 AM 7/24/04, you wrote:
>I do not quite agree with Rene.
>1. thermal mass can be reduced by applying only a thin mud-layer by
>spraying a slurry. This could be covered with wood, the way, saunas
>usually         look like.
>2. principally the bigger problem is the one with the moisture of
>course. But you use a sauna only a few ours a day, then you can take
>care about good ventilation.
>Due to the moisture-problem, especially as it is run mostly during
>cold periods (large temperature gradient, a lot of moisture, thus the
>threat of condensation), building a SB sauna really is a demanding
>task. And if it works (and I think it should), it would be a
>impressive example to argument with, in discussions with critics.

Rene Dalmeijer

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