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GSBN:Re: Danny Buck's moisture NM


Thank you very much for all of the feedback you have sent. It is all very

An update:

We did the original moisture testing by drilling holes, 5/8th of an inch in
diameter, as deep as we could into the bales, through an average 2-3" depth
of cement stucco with an elastomeric "Sto" color coat on the outside. We
drilled 26 of them, some the full depth of the bale and some until we hit
concrete, as the bales have internal 4" diameter concrete columns 18" on
center. Some areas were dry, with moisture readings under 18%, but 13 of
them had higher moisture content, as high as 36%. The moisture tended to be
either right under the stucco and/or under window sills. Two holes were
generally dry, with moisture only deep near the interior mud plaster. Both
of these holes were in a room that had a moisturiser running in it most of
the time.

We have now gone back after two weeks and checked the moisture in the same
holes again. We have had generally dry weather, except for one rain one
afternoon and the moisturizer has been left off. The readings in all holes,
at all depths, have dropped significantly, except for four holes, three of
which are close together. Three of the four are still over 18%, but dropping

The wing of the home that has the problems is two stories high with no
overhang. Our approach is to build overhangs at all windows, approximately
16" deep, fully weather sealed with a drip edge. This week we will be
removing approximately 9" of the first flagstone sill (from the window, out)
and will replace it with a metal pan buried in the wall, covered with a
bullnose plaster and relieved with weep holes. Thus, we have protected the
window and sill with an overhang and protected the straw with the pan or
flashing. We are concerned about the difficulty of removing the sills as
they are a continuous piece of stone approximately 24" deep, running under
the window and overhanging the bales both inside and out. We are considering
leaving them in place if there is no moisture problem , caulking them very
carefully and leaving them in the care of the overhang.

On a building science note, we are in a dry, cold climate in Santa Fe, New
Mexico. Therefore, it is best to have an interior wall surface with an
impermeable finish to keep the relatively moist interior air out of the
walls and a relatively permeable exterior finish to allow the vapor
diffusion of moisture needing to escape from the walls, preventing it from
condensing on the back of the cold exterior stucco. Sto has a permeability
rating of 22 perms according to their tech in Atlanta, making it
semi-permeable. A material with a rating of less than 2 perms is considered
impermeable. The interior mud plaster is permeable and will have a rating
much higher then 22, but I do not know what it is.  We do know that we are
backwards between the interior and exterior walls regarding their relative
permeability. Therefore, we are hoping to be able to take the Sto color coat
off without too much difficulty, but have not seriously attempted it yet.
What about the 22 perm rating? Is it sufficiently permeable or not? We are
considering trying to decrease the permeability of the interior walls with a
paint or moisture inhibiter, but have not yet made a final decision.
Thoughts on that? A German baubiologist we spoke to that works with SafeCoat
finishes strongly recommended against sealing the mud walls.

Another thought that we are seriously considering is to vent the walls. We
have found some round, off-the-shelf vents that fit neatly into a 1"
diameter PVC pipe. The PVC could be cut to fully penetrate the 2-4" of
exterior stucco and the vent could initially protrude and then flush out
with the new coat(s) of stucco. This idea is a result of the excellent
drying that has occurred with the wall being perforated over the past two
weeks. We thought of putting them up where they are protected by the
overhangs and perhaps some 8-10" above grade, in part, because the straw is
within 2-3" of grade is most areas. I've never heard of venting a wall and
would previously recommended against it for heat loss considerations, but
want to try it here. Thoughts on that?

Thank you to anyone who has read this whole treatise. Would love to hear
from you.

Danny Buck