[Cob] another cob oven question: cool spots

[Tys Sniffen]

I seem to have cool spots on the floor of my cob oven. after a 3 hour fire,
during which I stir the coals a normal amount.  I've built many a fire in my
time, but does anyone have any experience on solving this problem?

 

It's a 'earthen oven' standard 4 ft, fire brick floor.

Tys