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Re: GSBN:RE: dipped Bale Walls


An article and photographs for The Last Straw on your French dip method
would be most welcome. And for everyone on this list, I'm always glad to
hear from you about your methods, techniques, or projects. Always need more
technical information for TLS issues - and you're the best source for these
articles. Thanks!

Joyce Coppinger, Managing Editor
The Last Straw journal
GPFS/TLS, PO Box 22706, Lincoln NE 68542-2706 USA
402.483.5135, fax 402.483.5161

on 5.25.2007 3:55 AM, Rene Dalmeijer at rene.dalmeijer@...:

> 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
>> 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
>> 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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