[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: GSBN:Re: Danny Buck's moisture NM



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
about the performance of clay's ability to regulate the moisture etc.
As a side note, this was at Bioshield, not Safecoat.

-Sol

  Thanks

Danny

"In the dark of the moon, in flying snow,
in the dead of winter, war spreading,
families dying, the world in danger,
I walk the rocky hillside
sowing clover."

            Wendell Berry
_________________________________________________

> Dear GSBN
>
> Thank you very much for all of the feedback you have sent. It is all very
> helpful.
>
> 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
> slowly.
>
> 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
>
> ----
> 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.
>
> For instructions on joining, leaving, or otherwise using the GSBN list,
send email to GSBN@...HELP in the SUBJECT line.
> ----