[Strawbale] cement stucco problems?

[Rob Tom]

On Sat, 14 Oct 2006 19:24:08 -0400, Mark Bigland-Pritchard  
<mark at lowenergydesign.com> wrote:

> I saw one case of interstitial condensation, and it was so far gone that  
> I couldn't tell you whether the culprit was diffusing moisture or air  
> leaks or both.  However, when I did calcs to predict condensation ... I  
> found that condensation was indeed to be expected on the basis of vapour  
> diffusion through the wall in this one particular property.

> If, say, your walls are consistently at about 80% relative humidity(as  
> was the case in some  walls in the California winery monitoredby John  
> Straube some years  back), then they are at risk.


Okay! I like this.

In the first example above where moisture intrusion as a result of vapour  
diffusion was a suspect, it would be useful to know some of the building  
specifics.

For instance,
1. What type of construction was it ?
2. Was it built in a manner that would ensure relatively air-tight  
construction ?
3. What was the occupancy ?
4. What sort of conditions were on the two sides of the building envelope ?

In the second example of the California winery, was the constant 80%  
relative humidity:
1.  as a result of ambient outdoor humidity levels being that high or
2. as a result of extreme conditions created by occupancy/building type ?
   (ie tall building and/or large temp differentials between indoor/outdoor  
creating a condition where moisture was driven into the wall)


> and Rob Tom wrote (with rather less care):
>
>> As has been mentioned numerous times on these Lists recently, the  
>> plasters used on SB walls , at the thicknesses which they are typically  
>> applied, are sufficiently vapour impermeable and non-air permeable to  
>> make moisture movement through the plasters via vapour diffusion a  
>> non-issue.
>
>> Bulk moisture transport via leaks OTOH is another matter entirely and  
>> has nothing to do with relative humidities.




-- 
===* ===
Rob Tom
Kanata, Ontario, Canada
<archilogic at chaffyahoo dot ca>
winnow the chaff from my edress in your reply