[Cob] Tires For a Foundation?

[beno]

marie moser wrote:

> Have you considered using earthbags for a foundation instead of tires? 
> It seems like tires just create more work than is necessary.  I'm 
> assuming that the caliche stones are similar in size and shape to 
> gravel, so 2 or three courses  of  earhbag-encased stones should make 
> a good steady foundation without all the headaches of tamping tires.

Yes, I am considering 3 options:
* earthbags
* tires
* creating a raised area and a large, deep drainage ditch all around.

Regarding earthbags, how does that work? Just stuff the bags with 
caliche gravel and tie? Doesn't one have to worry about them 
deteriorating? What kind of bags does one use? The bags that, for 
example, grains are shipped in (nylon)?
Thanks,
beno