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Re: GSBN:Re Thermal Properties of Straw Bale Walls



Andre,

Thanks.  You're right, I completely misunderstood.  We actually could
possibly have done something essentially like that.  The way the Straw Dogs
(Turko Semmes and Greg McMillam, who helped on the project) did compression
in those days (1996), they used airline strapping and levered, ratcheted
tightening tools - not too dissimilar in design from the chain tighteners
that long haul truckers ("lorry drivers") used to tighten the chains across
their loads.  We Could, I suppose, have custom-cut a row of bales so that
once compressed, the rest of the wall (all but the tip row) left just
enough room to insert one last row.  ...then we could have released some of
the tension on the rest of the wall to tighten up the top row.  If I am
ever involved in testing a bale wall in a hot box again, I think I will try
that method.  Thanks!

Nehemiah Stone
stoneandstraw@...



> [Original Message]
> From: André de Bouter forum@...
> To: GSBN GSBN@...
> Date: 5/24/2007 2:08:50 PM
> Subject: Re: GSBN:Re Thermal Properties of Straw Bale Walls
>
> Dear Nehemiah,
>
> Apparently I did not get across what I intended to say. But it's not
> that important.
>
> As for stuffing the top of a post and beam structure, this is how I do
> it (and I'm convinced  it is almost as dense as the rest of the wall) :
> First place your bales to form your wall (* keep in mind that in France
> the bales are usually placed on on top of one another, squished between
> planks of 4x20 cm (2x4 inch))
> When we get to the last row that can be placed we do NOT place them.
> Instead we place a thick plank which we push down with a carjack. This
> pushes down the bales, eliminating any (horizontal) voids between the
> bales and making the wall a whole lot sturdier. We then prepare the
> custom bales that will fill the space between the last bales posed and
> the ring beam. To avoid stuffing with flakes (this is my main point) we
> place those custom bales vertically thus filling the space of the last
> row of bales + the space above it (and you bet you your bottom dollar
> that MY custom bales are as dense as any bale coming straight out of a
> baler ;-). When the custom bales are ready we take out the jack (the
> bales bounce up a bit) and place the bales. We use 'shoe horns' made of
> sheet metal to make sure the bales slide in as tight as possible without
> the need to force a lot (I hope the word 'shoe horn' is correct, what I
> mean is the metal object one uses to get in those very tight dancing
> shoes). By the way the sheet metal is folded on one end so that it is
> easily pulled out again. The bales will come up even more and this
> creates an even pressure throughout the wall (at least we think so).
>
> * car jacking a whole wall down is obviously tricky, but for a test
> panel this should not be that difficult.
>
> This said, I also like Bob's idea to cut out a piece of a larger wall.
> But cutting would need to be accurate and handling could be difficult.
> And I agree with wolfman that eliminating the the post and beam
> structure using big bales is a very interesting way to go (but one would
> need a crane to dip them ;-)
>
> Bye,
>
> Stuffed up André
>
> PS thanks Martin for Darrel DeBoer's email.
>
>
>
>
> Nehemiah Stone a écrit :
> > Andre said, " 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'."
> >>
> >
> > In an ASTM 236 Hot Box test, you do not have the opportunity/ability to
> > jack the wall segment up.  You build it upon the insulated (which is
> > pre-tested for conductivity) base, and you have a set opening size to
build
> > up to - which is why you have to stuff the top once you have compressed
the
> > wall segment.  If you COULD jack the wall up, you would be faced with
> > almost the same problem (only with jacks or blocks in the way) at the
> > bottom as we faced at the top.
> >
> > Nehemiah Stone
> > stoneandstraw@...
> >
> >
> >
> >
> >> [Original Message]
> >> From: André de Bouter forum@...
> >> To: GSBN GSBN@...
> >> Date: 5/20/2007 3:17:00 AM
> >> Subject: Re: GSBN:Re Thermal Properties of Straw Bale Walls
> >>
> >> An other very effective way to create a snug fit arround the posts was
> >> shown at the last ISBBC: Put a piece of lumber (that has the dimension
> >> of your post) on the ground. 'Drop' your bale onto it .Cut of the
excess
> >> straw that sticks out on the side oposite of the piece of lumber. "Et
> >> voila!"
> >> This trick only works for bales layed flat and with posts that are
> >> moderate to small in size. I forgot who showed us this 'gem' during the
> >> conference.
> >>
> >> 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 écrit :
> >>
> >>>> 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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