[GSBN] Steel mesh in clay plaster (?)

[Misha Rauchwerger]

Hi Marty, et. al.,

I have some anecdotal information to share.  I just did a small demolition
of a window in a cob structure.  I've attached a short video of some of the
demolition.  There was galvanized expanded metal lath on the underside and
vertical faces of a header that was embedded in the cob.  The window was
constructed approximately 17 years ago.  I was really impressed with the
tenacity of the cob, especially to the horizontal underside of the header,
which you can see in the video of me using a small jackhammer to remove
it.  Some old nails were also used for connection.  With regards to
corrosion, after 17 years, the lath had a minor amount of rust, but
appeared to have stopped, looking superficial.  There did not appear to be
any difference in amount of corrosion on the lath just under a thin layer
of plaster on the exterior face of the header, versus the corrosion on the
interior lath.  I have a feeling that once the cob dries, there is a minor
amount of shrinkage away from the metal, so even if it is still
mechanically attached, there is a small air space which limits the
corrosion unless moisture is re-introduced to the lath/earth interface on a
regular basis.

thanks for all your work on the subject.  I'm excited to do further
research with Art Ludwig with regards to FerroCob, as our scale model of a
FerroCob house had incredible performance on our small testing jig.  We'll
keep you posted.

Misha Rauchwerger
www.builtinbliss.com




On Sat, Aug 24, 2013 at 1:39 PM, martin hammer <mfhammer at pacbell.net> wrote:

>  Hello all,
>
> Can anyone weigh in on the use of steel mesh in clay plaster, in terms of
> corrosion of the steel?  In particular if it is susceptible to a higher
> rate of corrosion than steel mesh in lime or cement plaster (or what an
> expected service life might be).  Laboratory tested evidence is especially
> welcome, but so is anecdotal evidence (pro or con).
>
> I know there has been concern expressed about this for many years.  I’ve
> heard theory, but I haven’t seen hard evidence that it is actually a
> problem.
>
> I ask this in the context of a Strawbale Tutorial I am co-authoring for
> the World Housing Encyclopedia.  The tutorial is meant as guide for
> constructing small houses in seismically active regions of the developing
> world.  Thus the desire for a reinforced clay plaster as the in-plane
> lateral resisting system.  Darcey Donovan has used nylon fishing net in her
> system with PAKSBAB in Pakistan (which was shake table tested) but I am
> looking to use other mesh materials where such fishing net might not be
> available.  Metal mesh seems to be readily available in most of the
> developing world. (We are also considering natural fiber mesh, but these
> may have strength and degradation problems).
>
> Thanks!
>
> Martin
>
> PS – I’ve copied my colleague, Dmitry Ozeryansky, PE
>
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