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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 Glassford huffnpuff@...
- Date: Fri, 12 Nov 2004 14:58:42 +1100
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
G 'day DEsert Dave
See you are busy as always.
We need to be careful with moisture mate very careful.
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
My experience is now showing that we must avoid moisture in any form
getting into bale walls. No matter how good our detailing is when
moisture gets in it is very very hard for it to get out of a straw bale
wall without doing considerable damage on the way out that is, if it
gets to get out in the first place.
Straw will absorb a heck of a lot of moisture before it starts to travel
down and out through the bottom plates. Even then I have seen very few
bottom plates that have weep holes to allow moisture out. What happens
on the way out is that the straw will suck the moisture in to saturation
point and unless there is a drying mechanism in the walls somehow, then
the straw gets wetter and wetter and eventually starts to break down.
This can happen in a matter of days not weeks.
I think we have two areas here that are being discussed one is vapour
permeance and one is liquid water. To say a wall can breathe is
incorrect to say that it can exchange water vapour is probably correct
but at what stage does water vapour turn into liquid water? Do we want
to take the risk of this happenning?
Once the break down has started then it is too late as either the straw
will go mouldy or turn into a very wet black compost. I speak from
experience. So what to do?
1. Do not build in straw bale in high humid, high rainfall areas such
as the tropics.
2. Waterproof any straw bale walls in high humid areas of the house
such as a bathroom.
3. Build verandahs all round and keep all moisture off the walls in the
4. Make sure that the house has good venting to get rid of high
humidity mechanically before it gets to the walls.
5. Use a render mix that can handle moisture such as a lime earthen mix
or use an elastomeric paint that allows exchange of vapour.
I do not know the answer to this one but my experience again is showing
that the lime/earth/chaff mix is working well under all sorts of
conditions down under. Even when the moisture turned into liquid water
in great volumes in one house the render mix showed where the trouble
was because the grain in the chaff sprouted and pushed the finish lime
render mix off the wall!!!
John Starube wrote;
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 Engineeri
John I am not sure if I understand waht you are saying here? Do you
mean to that sealing the blaes is not a good idea by using a silcone
based paint? or by other methods? I like the use of silocone paints or
elastomeric paints such as Murobond. If we had not used Murobond on one
of our early buildings it would not be around today in effect it sealed
the building but I suppose not 100% water proof as they said that the
product allowed vapour permenace.
We need more testing for moisture problems the last frontier for straw
bale. Especailly for old straw wolf builder type chaps.
Kind regards The Straw Wolf.