[Cob] stabilised cob foundations (hold the earthbags)

[Robert Alcock]

It seems to me that if what you're putting in the earthbags is 
essentially cob (albeit stabilised with lime or cement, to make it 
waterproof) and the earthbags are just temporary forms, then you could 
just as well get by without the earthbags altogether. After all, we 
don't use forms to build cob, why should it make a difference if it's 
stabilised cob?
You would then have a cob wall all the way down to the ground, with the 
bottom half-metre or more stabilised with lime / concrete / asphalt. 
You'd have a damp-proof course of stone or urbanite or other non-wicking 
material in there, which I suppose would be the bottom layer right on 
the foundation, but wouldn't have to be.

An almost-all-cob wall - simple, easy and beautiful! Anyone tried it?

What percentage of lime do the experts recommend for that "fully 
stabilized soil", by the way?

Robert
www.lesspress.com


Date: Thu, 9 Aug 2007 22:24:22 -0700
From: "James from House Alive" <james at housealive.org>
Subject: Re: [Cob] Gravel Bag Foundations
To: coblist at deatech.com
Message-ID:
    <426f58490708092224u6b16323am2c286278b9acc7b1 at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

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