[Cob] cob oven problem?

[Monica Proulx]

Hi,
 Looking for an answer about a cobbed oven project. I am new to cobbing and
the list and have searched the list but not found an answer to my question:
 Does an outdoor cobbed oven take in air for combustion through the floor
between the fire bricks during the baking cycle once the door is closed?
 My son and I have dug a two foot deep hole (by four feet round) and I
dumped most of a donated batch of 7 (5 gal) buckets of broken cement rubble
into the bottom, before I discovered that it had the unmistakable odor of
cat urine. It had been sitting in the buckets for some time and I guess the
smell had gone dispersed somewhat from stuff on top of the buckets, and only
when I dumped did I smell it. Ugh! [I should have asked them why they were
busting up their basement floor, I thought they were putting in a bath or
burying a body, who would have thought of cat urine : ( ]. Since I didn't
have a place myself to dispose of the rubble and didn't want to return it, I
left it in place and then we put clean rebble on top and built a third of
our urbanite foundation. It is mortared on the outside ring (to prevent
mice, which we have by the hatful).
 Anyone have an idea how to seal off the foundation, or do I even need to
seal it off?. We have a couple more feet of foundation to build up, and
since I was planning on continuing to mortar the outside perimeter that may
mean that any draw of air up though the bricks (if there is any) will come
straight up from the bottom of my foundation where the "treasure" is buried.
This potential problem didn't occur to me til some days after the deed was
done, and I am now worried that cat urine odor (which has a half life of
several hundred years!) will come up into my oven. Anyone who has smelled a
hot home radiator with cat spray on it knows how intense that can get. If I
put a cob layer in the foundation would that be air proof enough, given that
cob breaths? Should I use plastic (am worried that will melt) or cement for
a vapor barrier?
 I have a sick forboding about this that is tough to shake, and hope that I
am worrying about nothing. I wish I had thought of this sooner and I would
have removed the stuff. We live a block from a river on a sandy silty soil
with a high water table and lots of rising damp and humidity, which often
magnifies smells.
 We were hoping to build the actual oven this weekend or next, so if anyone
has any suggestions before then, that would be great. If not, that's ok too.
 Thanks,
Monica