[Cob] Gravel Bag Foundations

[James from House Alive]

Peter (and others),


  James, I was also concerned about using a non-stabilized material for the
> wall foundations. Naturally, I wanted to avoid the cost - ecological,
> economic, etc. - of using poured concrete, so I was considering the gravel
> bag option, possibly double-bagging them to add extra stability.


No need to double bag.  As someone mentioned earlier, the bags are simply a
form to hold the tamped earth together while it is curing.  Once dry, you
could theoretically remove the bags and still have a stable foundation.  The
only thing that will break down the bags is sunlight, so be sure to cover
them as soon as you can.  I usually apply a cement stucco to the outside, to
protect them from the sun.  Also, I think we should not use the term "gravel
bags," as what we're really talking about are bags filled with "soil
cement."  The soil may contain some gravel, but loose gravel on its own
would not be a suitable option (IMHO), because it cannot be tamped and
compacted the way earth can be.  I prefer the term "earthbag."

  I also plan to use a rubble trench foundation, with perforated drain pipe
> at the bottom. Just to confirm, in your experience, bags filled with earth
> mixed with cement in the proportions you mentioned will provide enough
> protection from water damage even placed directly on top of the rubble
> trench? I was concerned that ANY earth mix - stabilized or not - could not
> be placed where it would come into contact with water.


In my experience the earthbags are durable in the situation you describe.
If you are concerned about standing water, you can always lay one course of
urbanite first and place your bags on that.  This would be some extra
insurance in especially wet areas.

  In Earthbag Building, the authors highly recommend lime for stabilzing
> soil, and say that "A fully stabilized soil is unaffected by water, and will
> remain stable even when fully immersed". That's for real, then? It would
> certainly make my life ten times easier. I just want to be sure that my wall
> won't come falling down after a particularly rainy season.


I have never used lime as a stabilizer, only cement.

Keep in mind that I have never built nor seen any buildings using this
technique that have been around longer than 4 years.

Good luck,
James

-- 
"If success or failure of this planet and of human beings depended on how I
am and what I do...How would I be? What would I do?"
-Buckminster Fuller

James L Thomson
www.housealive.org
7540 Griffin Lane
Jacksonville, OR
(617) 851-9628