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RE: GSBN: Lime & Cement Plaster
<x-charset iso-8859-1>Hi all. Sorry I have been silent on this, but I've been on the road.
The numbers in my report are actually not that different than other
published values from European research. Remember that the permeance values
are for specific thickness of stuccos -- thinner stuccos of the same type
are more permeable!
The conclusion is that the addition of lime quite dramatically increases
vapour permeance and reduces stiffness (this leads to less strength but
greater flexibility). The traditional (last 50 yrs) reason to use lime has
only been to increase plasticity.
Masonry cement does not have lime, but chemical plasticizers. I do not know
if masonry cement increases permeance, but I doubt it.
Lime is, within measuring accuracy, just as caustic as portland cement.
Remember of course that earth plaster is both more permeable to vapour (and
to liquid water. )
Dept of Civil Engineering and School of Architecture
University of Waterloo
Waterloo, Ontario N2L 3G1 CANADA
From: GSBN [mailto:GSBN@...]On Behalf Of Derek Roff
Sent: Monday, December 10, 2001 5:55 PM
Subject: GSBN: Lime & Cement Plaster
I checked my copy of John's report, and here are a few numbers:
1:3 portland cement to sand - 39 metric perms (0.68 US perms)
1:1:6 portland cement to lime to sand - 295 metric perms (5.13 US
These figures show that the addition of lime to a portland cement
stucco mix dramatically increases the moisture
permeance/permeability. I believe that the 1:1:6 mixture was the one
--On Saturday, December 8, 2001 12:21 PM -0500 Rob Tom
> While we're on the subject of plasters, perhaps some of you might
> be interested in the little-publicised, unpublished test report
> (don't ask me why, cuz man, I don't know) on the subject of :
> "Moisture Properties of Plaster and Stucco for Strawbale
> which GSBN listmember WatJohn (aka Dr. John Straube, aka the
> Truth-seeking Listowell Missile, aka Spice Flake, (who would never
> toot his own horn, I don't think he even owns a horn )) wrote for
> CMHC a couple of years ago.
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