Re: SB: skins of earth and cement

[Athena and Bill Steen <absteen@dakotacom.net>]

> 
> Need one be cognizant, that during the winter, when some interior heating
> will be required, and even though the interior earthen plaster will store
> excess humidity, it would be preferable that the interior vapour permeance
> be less than the exterior permeance?  In Raquel & Greg's situation, would
> decreasing the permeance of the interior by applying an appropriate paint,
> while keeping the permeance of the interior skin slightly higher than the
> exterior, be a viable compromise?  This would have the effect of reducing
> the rate of release of humidity to the inside during times of inward vapour
> drives, as well as reducing the movement of vapour outward through the
> interior skin during the winter.  I guess it all depends on the amount of
> exterior wetting, the amount of vapour produced in the interior, the
> ability of earthen plasters to store humidity, etc., etc.  Peter.
> 
> P. & P. Martin,
> 1830 Millstream Rd.
> Victoria, B.C., V9B 6E3
> 250-478-0073

I would think that decreasing the amount of water absorption by the exterior
skin would be desirable such as using Siloxane or similar product over the
lime/cement finish.  In ongoing experiments with plastered bales that
simulate patio walls I continued to be amazed at how much greater the
deterioration is of the bales whenever lime or lime/cement are used, even if
in the form of thin layers over earthen plaster.   Furthermore, it would
seem that the mild temperatures and lack of extremes in the northern
California climate and their given level of rainfall, etc. that an earthen
finish would be fine for the interior wall surfaces.  However, it has been
pointed out by Rob Tom who has been seeking to draw me into this discussion
that favorable levels of humidity adsorption only is a factor when air
exchange levels are in the vicinity of .25 per hour.  So.....but we have
noticed an appreciable difference in our bathroom in the amount of time
needed for fogged up mirrors to clear since the walls were plastered with
clay and sand.  Therefore I still have to believe that earthen finished
walls will have a beneficial effect on assisting in the relief of excess
humidity when it is generated within the building during the cold months of
the year and that it will help avoid large quantities from being transported
into the walls.  But after all, Rob Tom is the one who has sent me numerous
papers in the past stating that moisture damage as a result of vapor
diffusion is almost not an issue, that it is air leakage that is the real
culprit.

Bill
The Canelo Project
Athena & Bill Steen
HC1 Box 324
Canelo/Elgin, AZ 85611
520 455 5548
absteen@dakotacom.net
www.caneloproject.com




 
> 


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