[GSBN] Steel mesh in clay plaster (?)

[martin hammer]

Thanks for your 2c worth Graeme.

However your advice to “don’t do it” seems unduly emphatic for the evidence
you present.  I agree steel (especially thin gauge mesh) should be
galvanized or otherwise protected if possible.  Not only in clay plaster,
but lime and cement as well.  But one would expect the trowel rusting you
and Andre observed to occur.  It has the moisture and oxygen it needs to
rust.  However it seems that all the evidence and thoughts presented in this
GSBN discussion suggest that once the soil dries, the rusting arrests.

At this point I’m more convinced that steel (maybe even unprotected) in clay
plaster (or cob, as Art Ludwig has described) is not in danger of
significant corrosion.  I can imagine extreme conditions potentially
presenting a problem (e.g., at the base of a wall where a plaster is
routinely wet from frequent rain), but in general is seems to be safe
enough.  I’ve used Cintoflex also, and like it in many ways (though the
thought of plastic mesh in clay plaster sometimes makes me squirm) and I’ve
read about the use of geomesh yielding great test results.  But these
materials may not be available in developing regions where the Strawbale
Tutorial might be used.  I’m looking for an array of materials to choose
from, taking into account availability, durability, cost, and performance.

Martin


On 8/26/13 6:14 PM, "Graeme North" <graeme at ecodesign.co.nz> wrote:

> My 2c worth
> 
> Unprotected steel in clay plasters - don't do it.
> 
> In the NZ Earth Building Standards steel reinforcing is to be galvanised or
> painted with zinc rich paint or asphalt as a "belt and braces" approach even
> though we have little evidence of reinforcing steel rusting or otherwise in
> clay, but we were influenced by observations already made about how quickly
> steel tools rust if clay is left on them.
> 
> For plasters we are now using light polypropylene meshes such as Cintoflex D -
> or C if we want a heavier mesh. Its  much easier to use than any steel meshes
> I have seen, is compatible with clay, very cheap, and corrosion free.
> For any horizontal reinforcing inside earth walls we use heavier polypropylene
> geogrid square or triaxial  meshes, and shake table tests seem to give great
> results.
> 
> cheers
> 
> Graeme  
>    
> 
> Graeme North FNZIA
> Graeme North Architects
> 49 Matthew Road
> RD1
> Warkworth 0981
> 
> www.ecodesign.co.nz <http://www.ecodesign.co.nz>
> 
> 
> 
> 
> On 26/08/2013, at 10:49 AM, Kyle Holzhueter <nihondaigaku.kairu at gmail.com>
> wrote:
> 
>> I think it depends on the soil and climate.  Rule of thumb in Japan is to
>> avoid contact of earth plaster and metal.  In cases where it can't be
>> avoided, cover the metal lath with a alkaline plaster first.  As Andre
>> suggested, you'll notice how trowels not cleaned will rust differently when
>> working with earth and lime plasters.  I've also noticed that my trowels will
>> rust faster in Japan than North America.  I suspect that soil pH may be one
>> factor.
>> Regarding natural reinforcement, in traditional Japanese earthen storehouse
>> construction, there is a practice called tarumaki (barrel wrapping) that
>> involves embedding straw rope in wet plaster:  Vertical rope on roughly 20cm
>> centers, more plaster, than horizontal rope on roughly 20cm centers secured
>> with bamboo nails. Repeat depending on thickness of wall.  There's an
>> interesting instructional video series on this practice that used to be for
>> sale.  If anyone is interested, I could see if the videos are still
>> available.
>> I've attached two photos of an improvised non-traditional version on a straw
>> bale wall using palm rope.
>> 
>> Kyle
>> 
>> *************************************************
>> Kyle Holzhueter  PhD (Bioresource Sciences)
>> Nihon University, Graduate School of Bioresource Sciences
>> Architectural and Regional Ecological Design Studio
>> 1866 Kameino Fujisawa Kanagawa 252-0880 Japan
>> 
>> カイル・ホルツヒューター　博士（生物資源科学）
>> 日本大学大学院　生物資源科学研究科
>> 建築・地域共生デザイン研究室  
>> 〒252-0880 神奈川県藤沢市亀井野1866
>> 
>> TEL/FAX: 0466-84-3364
>> Mobile: 080-3477-9841
>> http://hp.brs.nihon-u.ac.jp/~cnes/index0.html
>> http://holzhueter.blogspot.com/
>> http://japaneseplastering.blogspot.jp/
>> *************************************************
>> 
>> 
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