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

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,

André "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@...


----
For instructions on joining, leaving, or otherwise
using the GSBN list,
send email to GSBN@...HELP in
the SUBJECT line.
----




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


--- StripMime Report -- processed MIME parts ---
multipart/alternative
 text/plain (text body -- kept)
 text/html
---
----
For instructions on joining, leaving, or otherwise using
the GSBN
list, send email to GSBN@...
HELP in the
SUBJECT line.  ----



----
For instructions on joining, leaving, or otherwise using
the GSBN list, send email to GSBN@...
with HELP in the SUBJECT line.
----



----
For instructions on joining, leaving, or otherwise using the GSBN list, send email to GSBN@...HELP in the SUBJECT line.
----