[Cob] More on Cob vs Cement

[ocean]

Most of us in the cob building movement love the curvilinear mode of 
construction, both for strength and aesthetics.  Have you ever been in 
a "round" building, or a cob house?  There is a sense of flowing form, 
"coziness", comfort - all qualities which can't be engineered or 
quanitified.  Still, many cob cottages in Wales are rectilinear, 
gaining their strength from being massively overbuilt - 3 foot thick 
walls!

I wonder why we are so concerned about the potential failure of cob 
(under a massive 9.0 quake) after just one seismic test.  Was the BC 
test conducted in a manner representative of quality cob construction?  
Any test of a cob structure must account for numerous variables.  I 
have several questions regarding the BC seismic test:

1. Why was there failure laterally, between cob "layers"?
2. Was the straw sewn through layers with "cobbers thumbs" as Cob 
Cottage Company teaches?
3. How much straw was added?  How was the ratio determined (test 
bricks, etc.)?
4. What was the clay/sand ration?  How was the ratio determined (test 
bricks, etc.)?
5. Did the layers dry between application?  If so, were the surfaces 
built with "ribs" to allow keying between layers?

Ianto and Linda emphasize the aforementioned techniques when they teach 
"Oregon cob", which they have developed to response to the seismic 
concerns of our region.  Was Ianto consulted on the method of 
construction for the BC test?  BTW: Have seismic tests been done on 
rammed cement-soil houses, or strawbale houses?  I'd be interested in 
these results for comparison.

One correction for Layth:  Concrete construction commonly contains 
15-20% portland cement, 80% aggregate sand/gravel, not 100% portland 
cement.  So some cement-soil construction actually approaches the same 
amount of portland cement as concrete!  Ianto Evans oft quotes that 
cement kilns produce 10% of the worlds greenhouse gasses.  Hospital 
waste (including radioactive material) is sometimes used to fire the 
kilns, resulting with cement that contains radioactive material!  I 
think we natural builders should use as little as possible.  In some 
cases it is necessary, such as outdoor patios, foundations, etc.

Lastly, I wonder if the need to conform to conventional rectilinear 
construction so as to be more acceptable to the "general public" should 
be a goal for natural builders.  I happen to believe most of the public 
would love to live in a curvilinear house, and once exposed to a cozy 
cob cottage wouldn't think twice about abandoning their stick framed 
box.  One anecdote: we have hosted the Seattle "Tribes Project" tour 
with an overnight stay in the cob Kiva at Ahimsa Sanctuary for the was 
four years.  This group is a multicultural theatre troupe of inner city 
high school kids who present a performance on race and empowerment.  
Without exception, each year the kids are amazed, ecstatic about the 
beauty Kiva.  One young man even burst out saying, "I'm going to come 
back and get married here!" ( http://www.tribesproject.org )

I encourage all natural builders to continue thinking "outside the 
box".  Sometimes the coblist seems to have a lot of conjecture, 
speculation, intellectual ponderings, too much for my taste.  At those 
times I just want to tell us all to get out there and get our hands and 
feet in the mud, to get building and post some pictures...I'll be 
getting some up of the Kiva soon!  Let's all keep cobbing!

Blessings,
Ocean

Steward, Ahimsa Sanctuary http://www.peacemaking.org
Proprietor, Intaba's Restaurant
http://www.intabas.com

On Dec 11, 2004, at 12:37 AM, laythss at yahoo.com wrote:

> Ian,
>   WHat I am trying to do in my thesis, is to see the eligibility of 
> cob (among other earth buildings) to be used in the mainstream 
> residential housing.  My only problem (for the general public) is the 
> test that was made in BC was for a round structure.  A round structure 
> is known to be stronger than a rectangular structure.  This is all 
> good for the exception that a round (curved wall) structure is not so 
> much a main-stream structure.  and yes using rebar might not be the 
> smartest thing, yet with my limited engineering background I think it 
> is still better than building with wood or concrete, since they impact 
> the environment far more than cob or cements/earth rammed earth 
> structures even if they are rebarrred.
> Ocean in regards to rammed earth, the cement/rammed earth uses between 
> 5%-15% cement in it, isn't this better than a 100% cement structure 
> environmentally. I know it is not the best, but wouldn't be a good 
> start?
>
> Layth