Cob Ferro-cement-Lime in clay

[Shannon C. Dealy]

On Fri, 30 Oct 1998, Mona Brookes wrote:

[snip]
> concerned about the strength of a wall other than in compression
> (earthquakes, car impacts, etc.), than you shouldn't be using cob or
> lime/sand.
> {snip}
> 
> You commented in a recent reply that cob could withstand car impacts... 
> is that true??

In the above reference, I am talking about cob used as a mortar providing
no real strength, this is because there is no chemical bond and very
little structural bonding between cob and the material being mortared.  In
the case of a car impact on a cob wall, the degree of damage would depend
on the circumstances, but cob should do considerably better than
conventional residential building techniques because cob bonds well to
itself and forms a single large structural mass.  Even ignoring the
strength of the cob, I would expect that it's mass alone would provide
better resistance to a car impact than a wood framed building.

> I was wondering how much protection it would give against some larger 
> wild animals... like bear... if a bear had in mind to push against or dig 
> through would it be successful??  ...any ideas on this??

I don't know that much about wild animals trying to break through walls,
though I feel certain a determined adult grizzly bear could dig through a
cob wall in a few minutes.  But of course that same bear could go through
the walls of a conventional house in even less time, and could knock your
front door off it's hinges in a few seconds.  Animals pushing against a
cob building shouldn't be an issue unless the animal weighs at least
one or two tons since even a tiny cob building would weigh quite a few
tons itself.

Shannon C. Dealy
dealy at deatech.com