[Cob] wall width and stucco...

[aaron allen]

greg asked, "how wide does a cob wall need to start
out and what width does it end up tapering to for a
two story structure,"
I dont want to sound too authoritarian on the subject
but I believe that the wall width is not the question,
even for two story walls.  I think that the most
important concepts are that the wall is vertical and
tapered toward the top.  secondly, curved walls are
far more stable than flat walls, and thirdly large
buttresses(flares) at the ends of your walls(at
doorways etc.) increase that stability.  there may be
some concern about the structural width/strength of
the wall at the top were it supports the ridge beam,
but cob is extremely strong in compressive
strength(weight loads that press straight down)  that
being said, I recently worked on a friends two story
cob house and the base width varied a great deal all
around the foundation depending on where he wanted the
 thermal mass.  the narrowest places in the foundation
were around two feet in thickness and rose to about
one and 3/4 feet at the top.  now finally, my opinion.
 I think that exterior cob walls should always be at
least two feet wide at the base in order to take
advantage of the thermal mass.  the tapper can be
minimal and some people only taper the outside face
leaving the inside vertical.  all of these
considerations can depend on the amount of resources
available to you, and your individual house.  ie: some
people choose a greater variance in their taper so
they will not need to mix, dig, or carry cob up two
stories needlessly.  consider the weight of your ridge
beam and what width you need to feel comfortable
supporting it, and then make your base wider than
that.  


as for question no. 2
"I've read that a lime stucco is used for the
exterior.
How and how often does one do maintenence on the
stucco?"
a lime stucco is just one of many different choices of
exterior plasters.  all plasters are meant to extend
the weather resistance of the cob as well as beautify.
 some people decide not to plaster at all, and bare,
well built cob has shown resistance to hundreds of
years of exposure to the elements in rainy places like
the UK.  as for the how, there are many good books
available on lime plaster work which could explain
better than I all of the concepts involved, and how
often would depend on weather, and appearance, and
quality of adhesion.  lime plasters, once well set are
very durable and could last a lifetime. 
let me know if this helped,
aaron
cobmailbox at yahoo.com   


		
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