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Re: GSBN:RE: dipped Bale Walls



Andy,

Would you care to write an article on your "french dip" method for the The last straw. Based on your mail you are probably besides Tom Rijven the most experienced user of this system. I have taken careful notice of your cob like approach making really solid walls.

I only used French dip on a few small projects until so far one of which was load bearing. The main gain for load bearing is the vastly increased stability of the wall whilst working on it. I am a keen convert to this method. Another bonus is that it allows you to use sub standard, not so dense/tight bales and still have quite a stable wall while building.

Rene
On May 24, 2007, at 19:35, Andy Horn wrote:

Hi all
Just to add my support of the dipping method.

Pre-dipping is for me by far my favourite way of pre-plastering Straw bale, and have found it helps shave hours and hours off the plastering process, resulting in a really sturdy solid impregnation of the plaster as well as helping with the pre-compression/settlement. Furthermore any risk of fire and weather is hugely reduced as the time that the walls (un-plastered) are at risk is a matter of an hour or 2 vs. days or weeks! I like it so much
that I have been doing it will all my projects for the last 3 years.

I first raise the wall for a good fit (allowing for shrinkage in the top course) and then sequentially take down the walls course by course. I then dip the bales in a bath of an adobe type clay/sand mix thinned down to a yogurt like consistency, taking care to only dip the surfaces that are to be exposed...helping with the weight and in maintaining the insulation. We use a non load-bearing on-edge system dipping panel by panel. We place the bales
in a bath of "slip" and then turning the bale over, use our hands and a
cobbing stick to really work the slip into the straw, usually achieving at least 50mm of penetration. We then allow the bales to partially dry out,
until they become more firm and tacky (but not hard)....more like the
consistency of cob. I sometimes call it "cob-bale" building because it is more like building with giant cob bricks. One sometimes needs to retard the
drying out of the first course/s of bales if there is a lot of wind or
strong sun so as to give oneself enough time to get all the bales dipped. As the walls go up, we immediately start to work the bales with a cob-stick to knit the bales together and help compact the coating. As straw falls off in the bath and makes the bottom too straw rich to dip with, we scoop out this mix and spread it out to partially dry to a cob like consistency and then
use this as our cob to help fill in any gaps around the base, eaves,
openings etc. I also use a small plank to whack the sides of the bales,
which also helps straighten and compact the coating. Plastering trowels are also useful for this task. The result is a wall that is really solid, that when tapped is closer to the feeling of a cob wall, avoiding having that partly disturbing hollow sound. From there on the subsequent plaster layers
are really easy to do.

If any of you want to see pictures of the process there are some on our
web-site.

Besides the above advantages mentioned my conviction in the dipping method has recently hugely re-enforced having this year helped a friend with the building of 2 load-bearing structures. The builder on site had neglected to
cover up and a huge storm blew in soaking one of the only half roofed
structures. We then had to prop up the roof structure and insert a pole
support system to convert the structure to a non load-bearing building. It was no fun having to rip out all the mouldy walls that had quickly started
composting.

In such regard, I would be interested to know if any of you have tried the
pre-dipping method with load bearing systems???

Cheers
Andy Horn

ECO DESIGN
Architects & Consultants
A. R. HORN - B.A.S. (UCT), B.Arch (UCT), Pr.Arch (SACAP),  MIA, CIA
Telephone: 021 462 1614, Fax: 021 461 3198
Cel: 082 67 62110
4th Flr, The Armoury
160 Sir Lowry Rd
CAPE TOWN
7925
www.ecodesignarchitects.co.za




-----Original Message-----
From: GSBN [<a target="_blank" href="mailto:GSBN@...";>mailto:GSBN@...] On Behalf Of Rene Dalmeijer
Sent: 24 May 2007 08:04 AM
To: GSBN
Subject: Re: GSBN:Re Thermal Properties of (french dipped) Straw Bale Walls

Chris,

I fully support you in this it is essential that the dipped bales are
used quite rapidly after dipping. This is a messy business but working
with two people to lift and place the bales makes a big difference. The
bales tend to fit in much better the need for stuffing joints is almost
diminished to zero.

Another tip once the bales are in place a tamping of the still tacky
bale surfaces with a plank and a hammer will align and flatten the bale
surface to a great extent. The best technique is to lay the plank
across the bale joints and then tamp. To work effectively the clay rich
slip should still be quite moist.

Rene
On May 24, 2007, at 03:50, cmagwood@...:

I'd like to kick in on the "French dipped" method, as I
believe they do a great job of helping to provide a really
good "seal" across the entire face of the wall. It would
make sense that if dipped bales are left to dry before
being stacked that they wouldn't work as well, but they
shouldn't go in when dried, but when slightly tacky. Then
the straw/clay that goes in the gaps bonds very well to
the bales and makes, for me, the best wall surface going.

Chris


Marty suggested that the 'French dipped' bales might give
a good tight
fit between the bales. My experience is the opposite. If
the bales are
dried after being dipped the diped sides get rock hard and
do not
compress. If the bales are placed before they are dried
there is more
chance for settling but this is a messier way of going
about.

As for the test Nehemiah mentioned where the top was
stuffed. A
suggestions (if such a test is ever to be repeated) is to
compress and
stuff the wall from below with car jacks between the
'foundation' and
botom plate'.

Bye,

Andr&eacute; "drop that bale" de Bouter



John Swearingen a ?crit :
Straw-clay seems the best material for this purpose,
although too
much clay
might increase conductive heat loss in the stuffed area.
<

...for several other reasons, too.  When straw is
stuffed in joints it's
relatively loose and so provides a ready channel for
moisture into the
depths of the wall.  Straw-clay will form a seal against
moisture
entering
the joints between the bales.  In addition, it stops air
infiltration and
can be screeded off to make a flat plain for plaster,
thereby reducing
the
occurance of cracks that result from abrupt changes in
the thickess of
the
plaster.  Also, it's fun to get dirty....

"Hurlen" John Swearingen

On 5/19/07, Martin Hammer mfhammer@... wrote:

Nehemiah -

Good explanations.

You talked about the straw-stuffed gaps at the top and
sides of a
wall as
being places where convective losses could occur.  So
I'll add the
thermal
importance of stuffing vertical joints/gaps between
bales for the same
reason of limiting convective losses.  (This would also
be important
between
bales and "posts" that go mostly or all the way through
the thickness of
the
wall.  I've seen I-joists or steel trusses used this
way.)

Straw-clay seems the best material for this purpose,
although too much
clay
might increase conductive heat loss in the stuffed
area.  Horizontal
joints
between bales don't seem to be an issue because the
weight of the bales
appear to cause the surfaces to lock in well enough to
limit air
movement
between them (although the French dipped bales might
seal that joint
even
better, and bales on-edge probably nestle together
better than
laid-flat).

Then there's always the question of what material is
between the
bottom of
the plates, and what the insulative qualities of the
roof bearing
assembly
are.  And then there's the ceiling/roof, and the
windows/doors, and the
amount of infiltration throughout, and . . . . .

Martin Hammer


John,

I did not see a response from Andrew.  Was that off
list?  I am always
interested in what new or other information people
have on the thermal
properties of straw bale construction.  Care to share
his input?
Also, your Q about how compaction affects R-value is
a potent
question.  If
hot box testing wasn't so expensive and time
consuming, or if there
were
funders lined up to pay for it, I'd already have an
answer for
you.  There
are a number of confounding factors, so until someone
has done the
actual
research, we can throw around lots of theories.
For example, it is air that creates the insulation
value of almost
everything used for wall insulation.  ,,,not the spun
glass, not the
solid
portions of the foam, not the cellulose, not the
straw.
Therefore, if
bales are compacted too much, one would expect the
insulation value to
go
down.  But, what is "too much?"  If bales are too
loose, then the air
can
circulate in the air pockets and research HAS shown
that this can lead
to
convective currents that lead in turn, to a dramatic
drop in
R-value.  That
was one of the causes (we think) for the relatively
low R-values in
the
ATI
lab tests in Fresno, CA.  Once we stacked the bales
in the hot box
wall
opening, and compressed them as they'd be in a
building wall, we had a
six
inch gap at the top.  We filled it with straw as
tightly as we could,
but
we are not match for either a baler or truckers'
strap tightening
levers,
so we KNOW that the top (where the greatest amount of
heat exchange
would
naturally occur anyway) was much looser than the rest
of the
wall.  Ditto
the sides, though those gaps were significantly
smaller (so perhaps,
harder
to compact straw into).
Further, though in theory greater compaction - after
the optimal
point -
will lead to a decreasing R-value, no tests have yet
shown that to be
the
case.  Perhaps we just haven't found the optimal
compression force
yet.
Perhaps the theory is wrong.
Lastly, I would question your assertion that jumbo
bales are
"naturally
compacted a lot more than the smaller bales."  It is
mechanically more
difficult to compact a larger bale to the same
density as a smaller
one.  I
am not saying that the machinery isn't designed to do
so - perhaps it
is.
But, from a pure physics point of view, it is not
"natural" as you
said.
One way to verify whether the compaction is greater
or not is to
measure
the water content and density.  Rice straw bales in
California (the
ones
we
tested) are typically at least 8 pounds per cubic
foot at a moisture
content of about 6%.  Do you have similar data on the
Aussie jumbo
bales?
If you want to get an accurate reading of the
moisture content (more
accurate than a moisture meter stuck a random depth
into the
bales), let
me
know and I will send you (offline) a description of
how we did it.
The
density (#/cf or kG/cM) is pretty easy, assuming you
can weigh a
representative sample of the bales.
Hope this helps.
Thanks,

Nehemiah Stone
stoneandstraw@...


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John Swearingen
Skillful Means, Inc.
Design and Construction
www.skillful-means.com


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