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RE: GSBN:Re: Danny Buck's moisture NM
- To: "'GSBN'" GSBN@...
- Subject: RE: GSBN:Re: Danny Buck's moisture NM
- From: "John Straube" jfstraube@...
- Date: Thu, 11 Nov 2004 22:29:31 -0500
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
Water will get in. Try to reduce it as muich as sensible, and balance
it with as much drying as you and the climate can provide. This is the
same set of rules for all buildings. Sealing the bales is sheer
madness, in therory and in practise.
I have reviewed the test data from the EcoHouse silicate paints and they
are truly amazing -- water repellent, vaor permeable, highly durable.
We should be trying them in the field more often, since the lab tests
are unequivocal that they work.
In New Mexico it makes little sense to worry much about rleative vapor
permeance. Control rain firsts, then air, and vapor will ake care of
School of Architecture and Dept of Civil Engineering
University of Waterloo
<a target="_blank" href="http://www.civil.uwaterloo.ca/beg">http://www.civil.uwaterloo.ca/beg</a>
From: GSBN [<a target="_blank" href="mailto:GSBN@...">mailto:GSBN@...] On Behalf Of Derek Roff
Sent: November 11, 2004 21:54
Subject: GSBN:Re: Danny Buck's moisture NM
I agree with David. It seems to be a common dream of builders and
designers to keep all water out, for ever. I suppose that we have a
dream of building perfect houses. Perfection might not be bad target,
but it's impossible to attain. The problem comes when designing for
perfection decreases quality, rather than increasing it. That has
happened many times on many buildings, when people believe they can keep
all the water out. These houses are the most likely to suffer
catastrophic failures. Examples include the many centuries-old adobe
structures, which were re-roofed and plastered in modern materials, in
order to "protect" them. A few were destroyed, and most suffered severe
damage over the course of a mere ten or twenty years, before the new
materials were removed.
Ahhh, but that was twenty years ago. Now we know better, and have
better materials. We are really going to protect those buildings now...
This relates directly to Danny's project. I suggest that there are many
advantages to leaving the interior mud plaster as is. I think that
sealing the plaster would do more harm than good. I doubt the
theoretical supposition, which Danny quoted, that the interior plaster
should be less permeable than the exterior plaster. Neither laboratory
research nor field monitoring support that approach. Rather, my reading
of the research tells me that having good permeability in all plasters
is the safest course for strawbale walls. Research by the Canada
Mortgage and Housing Corporation indicates that even in Arctic
conditions, the amount of moisture diffusing through a continuous air
barrier, from the living space into a wall, is small. On the other
hand, the amount of moisture moving with air through small flaws and
holes in the air barrier can be very large and have severe consequences.
While we should be vigilant in reducing these holes and flaws, as David
points out, it is hubris to suppose we can attain perfection in this
regard. Therefore, we need the broad expanses of permeable plasters to
ameliorate the effects of the inevitable moisture infiltration.
If it were my house, I would not seal or modify the mud plaster. I
think it is a big plus for moisture handling. Removing the elastomeric
from the outside would also be an advantage, in my opinion. I wish I
knew a simple way to do it. John Straube's testing indicates that vapor
permeable, water repelling coatings, such as siloxane, can be quite
effective over permeable exterior plasters. John Swearingen has
reported using this material with success and satisfaction in
California. I don't know if the silicate paints that Chris refers to
offer similar advantages. Independent testing is needed.
--On Thursday, November 11, 2004 7:11 PM -0500 Strawnet@...:
> Hello from Portland - a wetter place than my customary climate
> (Tucson), where I am attending the USGBC Greenbuild conference.
> I just need to reiterate a point I've made many times on this subject
> - that is the impossibility of keeping moisture out of these
> assemblies. If we can't keep moisture from getting into double glazed
> windows - two pieces of glass separated and sealed with the highest
> tech materials we can invent, built in a factory and put into a frame
> - why would you think we could build an assembly in the field, with
> the variability of materails, designs, workmanship and all that
> happens to those assemblies over time and water won't get in? It will.
> Take that as your base assumption and make sure it can get out. I
> can't say this strongly enough
> - things get wet, make sure that the drying capacity is stronger
> than the wetting mechanisms...
> Gotta go...
Language Learning Center
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