I keep thinking that ferro cement can be a great, cheap solution to many things. But it seems that everything I find on it looks like everything might be done where it doesn't freeze. Frost and cement seem to have issues. But maybe that's just the old slab style. One place where I think ferro cement could really shine is with a cob oven. It needs to be protected from the weather. A layer of ferro cement could do the trick. But if it is one contiguous piece - would it crack with the frosts?