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Re: GSBN:Moisture Problem
We have also had the splash problem from the scaffolding- it's very
easy at the end of a long day to convince yourself that the planks
are just fine where they are, even if they are under the drip line of
the roof. I'm not so surprised to hear that the moisture level is
rising in that outer zone of your walls; if the plaster is still wet,
the straw may still be absorbing moisture from it. My limited
experience has been that that outer 30-50mm dries very slowly, and
always experiences the most active cycling, from rain or from
On two projects we tried Tom Rijven's dip method, but it was so messy
and labor-intensive, and made the bales so heavy and the floor so
slippery, that we quit. But I wonder whether it isn't worth dipping
the exterior face of the bales, because if that outer 30-50mm were
impregnated with clay, I suspect that it would be alot more durable.
(Of course it now seems that you would want to let it dry before
plastering- we did not do this before.)
I can tell you what I'd really like- I'd like to be able to buy bales
that have been pre-impregnated with clay to a depth of ~75mm~ on all
sides, then dried. The core would retain its full insulating value,
while the exterior would become more moisture tolerant. Plus, the
strings would probably not matter any more; you would likely be able
to cut the bale open and lift out as long a section as you would
like, without the usual pop. And if the ends were nicely squared
off, we wouldn't have the funky corner intersections to deal with.
It really wouldn't be hard- a very large greenhouse, some conveyor
belts, a forklift, an efficient way of making and moving slip, and
someone could be in the business of producing some beautiful
eco-blocks. Maybe even in various, standard sizes.
I'd love to see a simulation- if you decide to look into it let me
know if I can pass on any information. In your project, is the earth
the finish material on the interior? And if so, doesn't that create
the opposite permeability ratios from what we have been discussing?
Thanks and best of luck with your project,
Thanks very much for your frank and open report on the McSweeney house.
I see some parallels to house I have just help complete. Since
plastering the exterior with a hydraulic plaster I have monitored the
moisture level. Specifically because we noticed a damp spot on the
exterior on the spot most exposed to weather that only went away slowly
after removing the scaffolding. The spot dried in about 2 weeks it is
not visible anymore. After doing some hard thinking I realized it was
caused by splash from water dripping from a roof drain on the scaffold
hitting the wall where the wet spot was only noticed after the scaffold
Now back to the parallel with the McSweeney house. The wet spot
prompted me to regularly monitor the bales around the house. We only
just plastered a few of the interior walls with earth plaster so most
places were and are easily accessible from the inside. Instead of the
moisture levels dropping, what I expected, They have been rising not
much but up from 14% to 16% and only on the very outside 30-50mm. The
wet spot is slowly drying albeit very slowly. The house is not occupied
yet and is well ventilated.
Your mail has warned me though to keep a careful watch on the house. As
I subscribe to your idea that the Scandinavian model of having less
permeable finishes on the inside and more open finishes on the exterior
is good practice in the Dutch type of climate. I would love to do a
dynamic moisture transport simulation to better understand what is
happening. Sven Eweleit of Andersehen might be able to help.
On Nov 10, 2005, at 17:19, Paul Lacinski wrote:
At the end of this email there will also be some questions- I
hope you all will have some ideas to share.
GSBN is an invitation-only forum of key individuals and
representatives of regional straw construction organizations. The
costs of operating this list are underwritten by The Last Straw
Journal in exchange for use of the GSBN as an advisory board and
technical editing arm.
Paul M. Lacinski
Mail: PO Box 107
Packages: 137 Beldingville Rd.
Ashfield, MA 01330 USA
+1 413 628 3800
View excerpts from Serious Straw Bale at:
<a target="_blank" href="http://www.chelseagreen.com/2004/items/seriousstrawbale">http://www.chelseagreen.com/2004/items/seriousstrawbale</a>
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