 Re: External crack
All,
I don't think hairline cracks are much of an issue. BUT, exterior cracks on an igloo will allow moisture infiltration, and that is not a good idea. Wet insulators do not insulate. As well, if you've ever seen the face of a house brick that's gotten wet, then frozen, you'll know that the force of the freeze-thaw cycle will kick the front of the brick right off. It's called spalling. Once the cycle begins, in a brick wall or an oven dome, it's virtually impossible to halt. I'd recommend that significant exterior cracks be ground out in a V and filled for just that reason. XJs on the right track with a flexible material of some sort.
Ji
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