Cob cob recipe

[Will Firstbrook WCB of BC]

Hi Graeme,

It is interesting that in discussions regarding the suitability of cob
in earthquake prone areas. People point to the Broadgreen house in
Nelson New Zealand which has survived without a single crack two
earthquakes yet the stone school down the same street has been rebuilt
twice. The house breaks many earthquake rules, such as thin straight
walls that have huge bay windows cut out of them, heavy slate roof,
large basement and built in a sandy area. Actually it is a very
beautiful house from the pictures I have seen.

What does the absence of cob as a standardized form of construction for
New Zealand mean?  I would be interested in a summary of these standards
is it available in electronic form on the web?

Regards, 
Will



>-----Original Message-----
>From:	Graeme North [SMTP:Graeme.North at xtra.co.nz]
>Sent:	Tuesday, August 19, 1997 12:33 AM
>To:	coblist at deatech.com
>Subject:	Re: Cob cob recipe
>Dear Will,
>
>Thanks for your reply - I understand the mechanism of clay shrinkage OK
>I am an architect that specialises in earth building of many different
>techniques - my concern with shrinkage is with cracking that has some
>severe structural implications when designing for earthquake conditions
>at least. The Standards New Zealand technical committee that I chair
>could not include cob as a "standardised" form of construction in our
>standards because no-one I have talked to yet who is familiar with the
>medium has been able to put a figure on a sensible limit on shrinkage
>for pre-construction material testing, although one Australian
>practitioner suggested zero. My own fairly limited experience with cob
>suggests that a good cob mixture will have shrinkage approaching about
>0.1 percent, but I need further amd wider consideration of a figure such
>as this - an iseal cob mixture as I see it will effectively not shrink
>at all as it dries.
>
>For your interest, Standards New Zealand has now issued for Public
>Comment three Earth Building Standards covering Engineering Design,
>Materials and Workmanship, and Earth Buildings not Requiring Specific
>Design.
>
>Further info on these world first comprehensive standards can be
>obtained from me or from Standards New Zealand :
>IANB at standards.synet.net.nz .
>
>Cheers,
>
>Graeme
>
>