[Strawbale] [Structural mesh &] Re: bamboo pinning

[Robert W. Tom]

On Thu, 27 Jul 2006 20:31:01 -0400, Jeff Ruppert <jeff at odiseanet.com>  
wrote:

> We don't use any pins anymore.
>
> I prefer to use chicken wire stapled to the top-plate/box-beam and to
> the sill plates, and then use sod staples to attach the wire to the
> bales.  We do this in vertical strips in the middles of bales panels,
> not over the entire surface.  It is far superior in terms of bracing to
> any pinning and is much faster.

Someone asked about the efficacy of using hexagonal-cell "chicken wire" in  
a structural capacity. I already deleted that message so I don't know who  
wrote the message and I can't quote it. Sorry.

As with any embedded tensile reinforcement (as in concrete or stucco  
apps), its tensile capacity doesn't begin to do any actual "reinforcing"  
of the plaster or concrete until the concrete or plaster has cracked.

At that point, the tensile capacity comes into play to hold things  
together and prevent the crack in the plaster or concrete from opening up.

By corollary, the tensile reinforcement will not provide any tensile  
resistance to the material it was intended to reinforce unless the  
reinforcement is fully embedded in the proper position within the cross  
section of the material that it was intended to reinforce. In engineered  
reinforced concrete components, the placement of the reinforcement within  
the cross section is a very nitpicky matter prescibed by standards. With  
the plaster skins of SB walls, typical practise WRT to placement seems to  
be ad hoc and haphazard (and presumably with complementary effectiveness.)

But WRT to SB walls, tensile reinforcements like hexagonal-cell chicken  
wire, rectangular-cell welded wire mesh, plastic meshes etc. also have the  
capacity to stabilise the straw bale core of the unplastered walls IFF (ie  
"if and only if" in MathNerdSpeak) if it is pre-tensioned to put the straw  
bales in compression, thereby providing the bales with some resistance to  
both in-plane and out-of-plane forces.

The efficacy of chicken wire mesh when used in this application (as it  
relates specifically to SB walls) can be reviewed in the CMHC document  
produced in 1995 entitled:

       "Developing and Proof-testing the "Pre-stressed Nebraska" method
		for improved production of baled fibre housing"


and in a related non-SB-specific but similar application in a 1996 CMHC  
document entitled:

	"Proof of Concept: Development and testing of the Biocrete House  
Construction
        System".

(both of these are available through CMHC (Canada Mortgage & Housing  
Corp), quite likely as free, downloadable PDF files but if not, they are  
definitely available in printed-on-paper form by requesting them through  
the CMHC website. Bottom line: In answer to the question: "Yes" even light  
22 gauge chicken wire can be used effectively as a structural  tensile  
element in stabilising unpinned SB walls )


That being said, how many times have you seen mesh, both the plastic  
variety and the steel wire variety, loosely-draped over the surface of the  
straw bales and then plastered over (so that it is effectively useless for  
anything and just a waste of time and money) ... or half buried in the  
surface of the straw so that it is only haphazardly embedded, if at all in  
the plaster so that it's doing very little if anything to provide tensile  
reinforcement for the plaster ?  (Sort of an "all Stetson with no cattle"  
situation in TexasSpeak.)

And that being said, not all plastic meshes are equal.

For instance, the Cintoflex ("D" and "E" lines) product that is made by  
Tenax is often mentioned as being used by SB builders.

The Cintoflex lines are made of a polypropylene fibre.
One of the properties of PP is that it is subject to stress relaxation,  
and that's not a Good Thing if the mesh is intended to function as a  
structural element in a tensile capacity.

I just noticed that I've not said one word about bamboo pins  yet so I  
guess I'd best shut up now before this intended-to-be-brief message gets  
any longer.


=== * ===
Rob Tom
Kanata, Ontario,Canada
<ArchiLogic at chaffyahoo dot ca>
(winnow the chaff from my edress in your reply)