Thanks for that, I did wonder how long it would last, even in the video I posted they were cooking in the cob oven that they had built and there were a few holes with smoke coming through the top.
Being were we live and very exposed i will make some sort of cover to at least help.
Thanks again.
Edit: The reason we chose this type is because the stone and clay are free, plus the little guys will enjoy it, if it doesn't last we will build another one by which time they will be skilled stone masons and cob builders