I have just took on the maintance of a building which part of the floor is suspended concrete. The problem I am having is with the concrete breaking away from the cast iron waste lines. When a toilet flange breaks and the concrete has broken away I am having problems securing the toilet. I have been using hydraulic cement to set the bolts in, but if to much cement has broken away, what I put in falls through. Anyone have any suggestions other than going underneath and bouiling a form around the waste pipes? It is a pain to get to from the bottom.