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GSBN:Re: Hydraulic Lime



Does hydraulic lime have the vapor permeability of traditional high calcium
limes?  My guess would be that it doesn't, but I haven't seen any figures.
How does the vapor permeability of the St. Astier lime render compare with
standard lime and portland cement/lime renders?

While it is impressive to claim minimal water penetration in the render
after the equivalent of four months of continuous rain, what that really
tells us, is that the material has properties that we don't need.  As
noted, we never get four months of continuous rain.  Such claims appeal to
a reflexive "more is always better" enthusiasm, and often disguise the
negative side effects of excess.  I think it is more important to have good
vapor permeability than to have extreme water resistance.  Especially if
there are concerns about ground moisture entering the structure from under
the house.

Standard lime renders have adequate resistance to water penetration, even
in wet British and French climates.  They have excellent vapor
permeability.  Lime putty can be stored for years.  The increased water
resistance of hydraulic lime is not needed, so far as I know.  Vapor
permeability is unknown (by me).  Hydraulic lime cannot be stored after
mixing with water.  Working time is limited.  In my view, these last two
factors make hydraulic limes inferior to standard limes for building
renders, especially for amateur builders.  No doubt there are some
situations where they would be appropriate.

Derek

--On Thursday, September 23, 2004 3:18 PM +0200 Martin Oehlmann
martin.oehlmann@... wrote:

St. Astier NHL2  is composed of 55-60% airlime and the rest hydraulic
lime.


Derek Roff
Language Learning Center
Ortega Hall 129, MSC03-2100
University of New Mexico
Albuquerque, NM 87131-0001
505/277-7368, fax 505/277-3885
Internet: derek@...