Re: SB: RV: CORRECTION TO THE (SB)ASICS OF LIFE

["Robert W. Tom" <ArchiLogic@yahoo.ca>]

7/31/90 11:53:50 AM, "Dane S. Judd" <dsjudd@entelchile.net> wrote:

>Conversely, though, if a cement plaster does _not_ permit trapped moisture
>to escape, that necesarily implies that moisture cannot _enter_  either.
>Thus, if the bales are below the maximum allowable moisture content to start
>with and if moisture cannot enter, then there is no moisture that needs to
>escape. Yet, the pro-lime team says that cement plasters are bad.
>
>This is the part that confuses me in all of the past discussions of the
>topic.  It just appears to be logical but, given the amount of knowledge and
>experience of those who advocate lime plasters, there must be something that
>I am missing.   What is it?

Dear Mr. Missing-a-brick-or-something;

Moisture can get into otherwise perfectly dry bales by the sun driving the moisture from rain-
soaked plaster into the straw (as well as from the interior from any number of sources.) 

The preceding would be true whether the plaster is lime, Portland cement or any other material 
that will take up water. (Actually, Portland cement plaster would likely soak up less rain than PC 
plaster.)  (Some wag would surely suggest vinyl siding as the ideal cladding for SB.)

Once that moisture is into the wall,  there isn't anything like the sun inside of the wall to provide 
the same amount of energy as the sun, to convert all of that moisture (much of which will  likely 
be converted to liquid phase somewhere within the wall) back into vapour phase so that it can be 
driven  back out through the plaster skin.

In cold climates during winter, where the air outdoors will have a very low moisture content and a 
large temperature difference in relation to the heated indoors, some drying to the outdoors may 
occur as Nature tries to equalise the differences. (Mother Nature is apparently a Socialist)    
However in really cold climates, it is also highly likely that the moisture may be in the form of ice 
and would likely have a difficult time finding its way out .

Lime plaster, being slightly more vapour-permeable than PC plaster, will permit water vapour to 
escape a bit easier than would PC plaster. 

In a capillary action tug of war (ie between straw and plaster, liquid phase water) it seems that 
the straw would win, unless of course it was completely water-logged in which case, you're 
pretty much $@#!*% anyway.

The moral of this story is that one should try to keep the plaster dry, no matter what the recipe 
may be. 

--- * ---
Rob Tom
Kanata, Ontario, Canada
<ArchiLogic@yahoo.ca>

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