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GSBN: Digest for 11/10/04



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-> Re: GSBN:Re: Danny Buck's moisture NM
     by John Glassford huffnpuff@...


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Date: 10 Nov 2004 21:43:37 -0600
From: John Glassford huffnpuff@...
Subject: Re: GSBN:Re: Danny Buck's moisture NM

G 'day Balers

Danny & Fionna Buck wrote:

>An addition to my last missive per my client:
>
>Danny,
>
>you might want to ask more specific questions about sealing the mud plaster
>on the inside. First, it should be noted, that the average thickness of the
>earth plaster is between 3-6 inches!!!
>This is a lot of clay in contact with the bales. The Germans I spoke to were
>discussing the clay's moisture absorption and control properties. They think
>it would be more harmful to seal it because then the clay could not preform
>any control because it would be unable to release moisture back out of the
>wall (yes, on the inside). So, the question should be what are people's
>observations about THICK earth plasters on the inside walls? Do people know
>
Just wondering if we have got the right end of the stick here when
discusing moisture and the movement of the same in a straw bale wall no
matter what render material is used.

My feelings these days are that under no circumstance should we allow
moisture to enter a straw bale wall in any form from the inside or the
outside.  Why take a chance on the moisture finding it's way out of a
wall?  Therefore I am of the opinion that we should make sure that
moisture in vapour or solid form cannot get into a bale wall.  Therefore
we should treat the finished coat of render accordingly and use methods
and materials that will give a water proof wall from BOTH sides.

This may go against all that we know about straw bale walls but the
school of hard knocks has taught me to be careful when saying that a
straw bale wall breathes or that straw is water permeant and so on.  I
now do all that I can with good details and good waterproofing to make
sure that moisture cannot enter the walls in the first place.  Therfore
good venting in any straw bale building has top priority as does good
details around window and door penetrations.

In answer to the specific question on depth of earth and moisture egress
I have found that with a 2" earthen render it takes a lot of driven rain
to get anywhere near the straw that is with a pure earthen render
without any sealants.  With a lime finish or a lime/earth finish to a 2"
wall I have had NO moisture penetration on exposed walls.  So I would
assume that even thicker earthen renders would pose no problems as well.
 We still need to do more work on this area of moisture and rendering of
straw bale walls.  All our bathroom straw bale walls are 100% moisture
proof and we get rid of teh humidity through good vents in the ceiling
and through the windows.

Kind regards John Glassford
<a  target="_blank" href="http://strawbale.archinet.com.au";>http://strawbale.archinet.com.au</a>
61 2 6927 6027




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