[Strawbale] Lego blocks from Straw

RT ArchiLogic at yahoo...
Fri Dec 18 21:03:03 CET 2009

On Fri, 18 Dec 2009 07:07:49 -0500, Marc Huebner <marchuebner at gmx...>  

> 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"),  
       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  

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 at 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 >
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