SB: Re: Stucco breathability issue help

[Rob Tom <ArchiLogic@yahoo.ca>]

9/30/2002 9:45:10 AM, patrick.hearn@sasktel.sk.ca wrote:
> many stuccoer's...  say the biggest problem is that most stucco is 
>put on too thin. 

>David5430@aol.com wrote:

>>Swarthmore College Strawbale House Project ...mentioned that 
>>moisture is a big issue with Straw Bale construction and walls 
>>that are completely sealed can hold moisture and cause
>>the straw to rot or break down. Is there a stucco that breathes so 
>>this problem doesn't occur?

David;

I think that if you have a look at the report that WatJohn (aka Dr. 
John Straube to non-SBHeads) did for CMHC under Don Fugler's 
watchful eye (his other one having a tendency to stray ?) a couple(?) 
of years ago, there will be vapour permeance/permeability numbers 
for various plaster recipes. (Downloadable PDF document at:
http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/00-132_e.pdf

One should be aware that "breathe-ability" (or more correctly, 
vapour permeance) works both ways; more vapour-permeable 
plasters also allow moisture to enter the plaster (& bales) more 
readily.

Rather than futz around with chemistry in an attempt to trick water 
into behaving (a losing proposition IMO) a better strategy is simply to 
not allow one's walls to get wet .

That being said, "moisture" is a "big issue" with most building systems 
and stucco finished (conventional, non-SB) walls in particular. There 
are on-going lawsuits worth $$multi-billions in the courts dealing with 
this matter as we speak  

Furthermore, Mr.Moisture's dear cousin, Ms. Mould, is also stepping 
out to the forefront as a "big issue" in conventional building circles 
these days and in this regard, one should mention that straw is an ideal 
host for one of the deadliest family of moulds, the stachybotrys mob.

As to Patrick's suggestion that "thicker stucco is better" , the point is 
de-bait-a-bale.

With the claddings that we use to cover our bodies, one notes that a 
thin cotton shirt will dry out a lot more quickly than will a bulky cotton 
sweater after a good soaking.

The downside to a thick plaster with a high moisture storage capacity 
is that when the sun comes out, it is  highly likely that the moisture 
stored in the plaster will be driven *into* the straw rather than 
cooked off (ie outwards to the atmosphere) and if the interior skin 
isn't very vapour permeable, well, you know. And one should also 
note that vapour permeances are cumulative.  

        ~~~ * ~~~
         Rob Tom
  Kanata, Ontario, Canada
<ArchiLogic@CHAFFyahoo.ca>
(winnow the "chaff" from my edress in your reply)

Please visit http://www.theHungerSite.com daily





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