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Re: GSBN:Re: Moisture in SBW
- To: GSBN GSBN@...
- Subject: Re: GSBN:Re: Moisture in SBW
- From: Derek Roff derek@...
- Date: Wed, 20 Oct 2004 16:57:03 -0600
- Reply-to: "GSBN" GSBN@...
- Sender: "GSBN" GSBN@...
I am guessing that this house is in the Santa Fe, New Mexico area. I grew
up in Santa Fe style houses in Albuquerque, which has half the rainfall of
Santa Fe. None of the houses I lived in were strawbale, but all the
flat-roofed ones had serious, recurrent moisture problems in the walls and
ceilings. This won't surprise many builders, but most home buyers seem to
be unaware of the risk.
I concur with John and David, as I suspect you do. Protecting the walls
with a pitched roof and proper overhangs is the easiest way to the
long-term success of your repairs, and probably the only reliable approach.
I hope the owners can be convinced of the beauty as well as the superiority
of the other Northern New Mexico tradition, pitched metal roofs.
I have a few comments on some of your items. On item 1, I think we need
more information on the current coatings, both inside and out. You mention
"mud" on the inside, which I take to mean an earthen plaster. Does it also
contain a binder, oil, or other admixture?
Outside, my guess is a little different than Barbara's. I am guessing that
you have a thin (1/8" or less) coating of the elastomeric, over a more
conventional one or two coats of portland cement/sand stucco, with embedded
stucco wire mesh. Is this correct? If not, please tell us what you can
about the coating.
Item 2. It seems likely that you will need to remove the bales below each
window where the moisture is really high. It may be possible to leave the
sill and window in place, and install your proper flashing and drain pan
underneath the sill, before reinstalling the insulation. This assumes
reworking at least some of the plaster inside and out, but that is probably
a given, in replacing the bales.
Item 3. Concrete loves moistur,e probably as much or more than straw does.
I am not surprised that you have found it also to be very wet. Drying is a
challenge, especially beginning in late October. Adding heat, as John
suggested, is a mixed blessing. It speeds drying, but promotes the growing
conditions for mold. Drying at lower temperature can inhibit mold growth.
However, this requires low humidity and lots of air movement. Standard
fans will move a lot of air, but not with any pressure or penetration. The
best available tools for drying that I know of are woodworkers' dust
collectors. Portable dust collectors can be found for $100-$200. These
radial blowers can suck and/or blow against moderate static pressure.
Therefore, they can move some air through a bale, and get a little
penetration in your drying. Depending on the situation, using a duct to
suck air from and through the straw to be dried may be the most effective
approach. Lots of air movement is most important, whether you add heat or
not. Drilling small holes in the bales, perhaps 1" in diameter, might make
it possible to increase the depth to which you could dry the bales.
Restuffing the holes afterwards would be a simple task.
I've often wondered if injecting an inert gas under pressure could help dry
bales with deeper penetration and less risk of mold. Nitrogen and carbon
dioxide are inexpensive, and fairly inert. The bottles used by welders are
portable, and contain no water. Forcing the gas through a damp bale, the
gas would pick up a great deal of moisture from the straw as it warmed to
room temperature. I don't think this would be feasible for large areas,
but might be worth a try in a small, wet, complex location. Since I
haven't done this experiment, I wonder if the nitrogen or CO2 might
actually be food for some micro-organism. I would bet that a truly inert
gas like argon would be too expensive to use.
Item 4. Like you, I see problems with inserting new bales into the bale
block grid, to replace the bales that must be removed. I don't know of a
workable material that would provide the solidity and support to the
plaster surfaces that the bales did. Perhaps you can build in some sort of
sheathing or substrate in those areas, and insulate with rice hulls or
blown-in cellulose. Particularly below the windows, and in small areas,
rice hulls seem like a good choice to me.
Item 5. It seems like the designer and his/her insurance might also be
involved. If the builders followed the architects instructions,
particularly on flashing and window details, then their liability may be
limited. The overall roof design is lame, but since it is traditional, I
doubt that the flaws in the roof design will be covered. Ignoring modern
window and door details might create a liability.
On the earthen floors, I would talk to an expert before replacing them.
There are probably some good folks in Santa Fe. I know that the crews in
Crestone have had great success with rugged. Talmath Messenbrink is one
authority that I would want to look at the floor, before I did anything
I'm going in for foot surgery in two days, but after recovery, if it is
still timely, I would be happy to volunteer a little time and see if I
could help on the project.
--On Tuesday, October 19, 2004 5:56 PM -0600 Danny & Fionna Buck
Haven't spoken up for a while, but am following what's going on. Thanks
for all the good SB energy.
I have been called in to look at a house that I did not build, but was
showing a spot of moisture in one of the interior walls in the mud
plaster.After some investigation, we have found extensive moisture
throughout one wing of the house.This wing has a flat roof with no
overhang. The other two wings have overhangs and are testing dry.
Moisture in the former is as high as 40% in spots, but a lot of areas in
the low 20% range. The pattern seems to be mainly under the flagstone
window sills (about 8" deep and probably without any flashing under the
flagstone.). The other main factor seems to be that the entire house has
elastomeric stucco. The owner has been caulking cracks in the stucco,
which appear to be caused by moisture buildup- ie the areas along cracks
tend to be very wet just below the stucco.
The house was built with a system local to our area caled "bale block".
This a system where two 4" diameter holes are drilled through each bale
prior to it being laid into the wall. After two courses have been laid, a
4" PVC is used as a form and a reinforced concrete column is poured
through each drilled hole, the PVC then being extracted. At every other
course, a 2" reinforced "beam" is poured the width of the bale. Thus we
have a concrete grid running vertically and horizontally throughout the
The owners are committed to making the house right (and rightly so for
everyone's sake). Here are some questions under consideration:
1. We want to strip the house entirely of the elastomeric stucco,
replacing it with a cementitious color coat where the walls are dry. We
are thinking of sand blasting it off. any other ideas?
2. The stone sills run the full depth of the straw bales, with the windows
set on top of them. Is there any realistic way to make this waterproof
without tearing out the entire sill?
3. We are expecting to tear out straw, wherever it is wet. Ibelieve it
will be difficult but doable in spite of all of the concrete. I am
thinking that we can get some drying once the walls are opened up, but
doubt that we can expect to really dry more than a few inches from the
surface. Can we dry deeper than that? What parameters shoud we use in
deciding how much straw to extract? When the moisture meter hits concrete
in wet areas, the concrete is as wet or wetter than the bales. Why?
4. Once straw is pulled out, with the concrete grid still in place, what
can we possibly refill the walls with?. The moisture tends towards the
outside of the walls, so we are hoping to keep the interior surfaces
intact and just work from the outside.When refilling the walls, we want
to keep moisture to a minimum, so straw clay or other poured or puddled
materials seem unlikely. I do not see how to use straw realistically-
would that be possible? We are going into winter here.
5. I have not had a chance to investigate any possible coverage from
liability insurance the original contractor may have carried. Would we
expect this to apply? The house is about 4-5 years old.
I am sure that other questions will arise as we proceed. This a very
beautiful home, with lovely interior finishes. One problem inside is that
the clay floors are wearing poorly around furniture. They want it replaced
with colored concrete. Any ideas on this?
Look forward to a response. Anyone want to do some volunteer (or perhaps
paid) work on forensic straw bale?
Santa Fe, NM
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