[Cob] cob in post and beam

[Buckaroo Bonzai]

Lance,

The information Darel provided was given by experts in
the field.  There was no comparision data with
concrete so I can't comment on that.   There is no
single % of moisture content as it will fluctuate
somewhat with the  ambient humidity of the air.  It
will not go above a certain point.   But, the experts
say, based on experience in the real world, that the
(at least the old type of heavy iron content nails)
will rust in cob or a wattle and daub.  This knowledge
is at least specific to areaa with a relatively high
humid summer and dry winter environment.

>Furthermore, I can't see how dry concrete which I 
>though was not water permiable and dense to hold 20% 
>water.  Also I feel that your figure of 4.5% is
simply 
>too low for cob.  Would you provide references and
>links to your data for confirmation?  Cob can and 
>does get higher than 4.5%, but not >high enough to
>support fermentation of the straw >embedded in it.
>Sorry I don't have the time to get >the figures or 
>referrences avail right now.  Some one >else out
there 
>might.

>Darel in response to Lance Collins's mail below


--- Lance Collins <collinsl at bigpond.net.au> wrote:
> But I 
> clearly recall a posting a few months ago which
> quoted equilibrium moisture 
> levels for various materials.   Concrete had the
> highest moisture retention 
> at about 20% and adobe was quoted at 4.5% having the
> lowest moisture level.

> 
> >Forward to group:
> >
> > >Rebar in concrete allowed to rust, weakens the
> > >structure and has been the cause of buildings
> > >collapsing, due to the exposed rebar which rusted
> > >through (eating through (oxydizing?) by moisture
> and
> > >air by)
> 
> Yes but the whole idea with reinforced concrete is
> to cover the rebar with 
> enough concrete to stop moisture getting to the
> rebar and causing concrete 
> cancer.  Usually this is about an inch for concrete.
>  I don''t know how 
> much for cob but I would think that a moisture level
> in cob high enough to 
> rust steel would also be high enough to cause the
> cob to fail in a short 
> time anyway.
> 
> 
> 
> > >Cob, modifies moisture in dwelling and can hold
> more
> > >moisture than concrete walls.
> >
> > >So rust proof materials would be a solid decision
> for
> > >humid areas.
> >
> > >Darel
> >
> >--- David Knowlton <pilot1ab80 at hotmail.com> wrote:
> > >> rebar in concrete is allowed to rust. rough
> oxide
> > >> provides a nice
> > >> grip for the concrete. just a thought
> > >>
> 
> I think what was meant was that the rebar is allowed
> to rust before 
> installation not that rusting continues after
> construction.
> 
> 
> Lance Collins
> 
> > _______________________________________________
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> 


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