I have a concrete collar which sits just above floor level in my bathroom, this collar is about 8" wide and seems to have concrete around it. the issue i have is that i can't fit my new toilet over it as the collar is to big. i am planning to remove this collar but am worried that i may crack the clay soil pipe if i try to break it off. does anyone know a trusted way of removing these collars without damaging the clay pipe.
You are correct indeed to be worried about damaging the clay pipe. In theory, the "concrete" you mention should in fact be a weak mix of cement that you should be able to remove carefully with a chisel.
Unfortunately, this is not always the case. If the cement collar cannot be removed in this way, an angle grinder with a diamond blade usually sorts the problem but be wary, if you crack the pipe it will leak and because of its position, is difficult to repair.
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