Rethink Your Life!
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The Work of Art and The Art of Work
Kiko Denzer on Art



[Cob] continuous foundation reinforcement

Amanda Peck ap615 at hotmail.com
Mon Jan 3 18:41:16 CST 2005



I like the idea of a Frank Lloyd Wright style rubble trench foundation (or, 
slightly different, a Frost Protected Shallow Foundation often mentioned on 
the same sites) with a drain to daylight in the bottom and a bond beam 
(and/or block, or stone, or urbanite on top).  It would be more work for you 
(think pounding the gravel into the ground until it rings!) than if you had 
someone else come in and pour the concrete, BUT....

The reason would be that your wall is going to be pretty thick, and your 
foundation needs to be right at that same thickness.  You need to have 
something other than cob up for a stem wall--6-12 inches above ground.  
Putting all of that in concrete might well  be a LOT of concrete.

I also think I would not use any rusty barbed wire that you had hanging 
around, if that's what you meant by "local."  It would probably just 
continue to rust until there was only a brown hole left.

What they sell around here is really rusty looking rebar or that heavy 
welded wire fence stuff, also looking very rusty.  I've been dubious about 
that stuff too, for the same reason.  But rebar is a lot thicker and 
presumably stronger than even new barbed wire.

(I'm prejudiced here.  Maybe unnecesarily.  Years ago a major freeway bridge 
in Nashville failed, although not catastrophically, because of rusty rebar.  
Winter salt on the concrete bridge combined with some inevitable cracks and 
fifteen years or so later there were some goodsized holes looking down many 
feet to the river--the salt, of course, played a major role in this.  Rebar 
may work perfectly nicely in a stemwall or foundation, but I think I'd ask 
someone.  Of course while a building is subject to earthquakes, it doesn't 
get the continuous rumbling that a very very busy highway bridge gets.)

Here's a kind of random link for the frost-protected shallow 
foundation--from the Home Builder's Association.

I haven't posted this link in a couple of months.  The .pdf file of 
designing earthen buildings for--not just--earthquake country by the man, 
Gernot Minke, whose house was in a natural building magazine a few months 
back.  Unfortunately, his house isn't in this link, and it doesn't come up 
in the first page with a search.  I think he really does have earthen sinks 
(with or without some concrete).

www2.gtz.de/Basin/publications/books/ManualMinke.pdf

By the way those of us who DON'T live in earthquake country shouldn't get 
too cocky.  In Sarah Andrews' mystery Fault Line, her detective asserts that 
a small earthquake that would hardly be worth reporting in earthquake 
country could be totally devastating in, say, Boston--and shape of the sand 
is a big reason.  The book may tell you more than you ever wanted to know 
about earthquakes and buildings, but it's set in a mystery story (not 
necessarily recommending the 500-pound gorilla of book sales to purchase a 
fairly recent paperback, but its an easy way for all of us to see the 
cover):

http://www.amazon.com/exec/obidos/tg/detail/-/0312984456/ref=pd_sim_b_6/102-7887725-1522507?%5Fencoding=UTF8&v=glance


.......
Susan wrote:

I am about to get started on an approximately 11-foot diameter circular cob 
building - off-grid and under 120 interior square feet (no permit 
necessary.)  I plan to dig a footing trench, fill it with concrete to grade 
level, and build a stone stemwall above that.  I'm building in earthquake 
country- the southernmost Sierra foothills at 3,500 ft elevation.

I'd like to use as much on-site material as possible, but part of me also 
wants to make it as solid as possible and document the process for future 
interactions with building officials.

My question is: What do you think of using barbed wire as reinforcement in 
the concrete instead of rebar?  Any ideas?