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Re: [Strawbale] Lego blocks from Straw
On Fri, 18 Dec 2009 07:07:49 -0500, Marc Huebner <marchuebner@gmx...>
wrote:
Does anybody know what kind of glue the guys from oryzatech are using?
This sounds like they are using some kind of thermoplastic!?!?
The blurb that I saw in the link that Duck Foo'd provided mentioned
"polyurethane (MDI)" as the binder.
MDI = Methylene diphenyl diisocyanate ("cyan-ate" as in "cyan-ide"),
C15-H10-N2-O2
fairly innocuous but a potential allergen/sensitiser and in a fire
the plast-e-c-chhh will generate toxic smoke.
But for that matter, many people are allergic to straw (or more precisely,
the allergens that are often found on straw) and in any fire, it is
usually the smoke, not the fire that kills.
That being said, as any woodworker can probably tell you, steam-bening
wood is a process of softening the lignin binding the wood fibres
together, thereby allowing the fibres to slide past one another during the
bending process without fracturing the wood and upon cooling, the lignin,
like a thermoplastic, solidifies again, fusing the fibres together again
and retaining the bent shape.
I would have preferred to see the Oryzatech people utilise the straw's
lignin as a natural binder rather than the plast-ecch!
one but I suppose that there's be a trade-off in terms of manufacturing
energy required.
I'm not too fussy on the blocks being designed to accommodate steel rebar
and concrete in the cores for stiffening either in the same manner that
foamed plast-echhh! stay-in-place insulating concrete forms (ICF) are
erected.
Baleheads long ago learned that core-stiffening elements like rebar or
threaded rod placed at the neutral axis of the wall section is the least
effective placement for those elements, not to mention that placement at
that location is a major pain in the butt (PITA).
I think that Oryzatech would have been better off simply keeping the block
cores solid and perhaps providing a series of surface channels which could
be used to accommodate exterior tensioning elements (if preferred over
simply using tensioned mesh) and/or electrical wiring.
and elitalking <elitalking@hughes...> wrote:
I am wondering how tight the construction is. Is it relying on the
stucco or other layers to provide air barrier. It mentioned structural
qualities. Is exterior sheathing required? Does the rigidity of the
interlocking elements sufficient to provide lateral bracing?
Having never seen one of the blocks and assuming that the pee-you binder
fills the interstitial voids between the straw fibres, I suppose that if
one were to dip the blocks into a clay slip before setting in the same
manner that Meathook (aka Norbert Senf) dips and sets the firebrick for
his masonry heater cores, the combination might be relatively air-tight
but I suspect that the wall system would still require a wet-applied
plaster in order to provide an effective air-seal.
I suspect that non-seismically-active areas, in-plane shear wouldn't be
much of an issue, and at most, some diagonal tension straps at the
building corners might be required.
Out-of plane lateral resistance... ehhhhh, maybe not so much. I'd be
inclined to mimic the exterior tensioning systems developed for real
strawbale construction.
I like that someone is looking at utilising straw to make a more uniform
building block than the toilet-paper-for-livestock
bales that straw builders are using now, however at this point, I'm not
convinced that Oryzatech has got it right yet. Maybe their Beta version
will be closer ?
Years (decades ?) ago, a Quebecer (Louis Gagnon of the concrete + bales
honeycomb wall fame) took the approach of modifying a standard baler to
produce better-quality building bales. [Mentally balancing/comparing a
Louis Gagnon modified baler all-straw bale in one hand vs an Oryzatech
plast-echhh! + straw legoBale in the other]
And according to the Oryzatech promotion blurb, their 15 lb per cu ft
block yields a wall that is triple the R-value of a conventional 2x6 wall
? While I suspect that the polyurethane content may contribute something
to enhancing the R-value of unadulterated straw, I strongly doubt that it
enhances it to the point of providing almost R-60 in Murrican units
ft^2*hr*degF/Btu (or RSI 10.57 in metric units m^2*degC/W ).
=== * ===
Rob Tom
Kanata, Ontario, Canada
<A r c h i L o g i c at Y a h o o dot c a >
(manually winnow the chaff from my edress if you hit "Reply")
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