I didn't get an answer to this post in flooring so maybe you plumbers have some experience with this problem, just hoping:

We are trying to figure out what to do with an old bathroom floor. It was never level to start with as the original builders in 1920's poured a rocky mortar mix over the studs and then stuck in a cement layer with tile on that. The tile has a few cracks. The drain pipe from the toilet slants and it looks like a stud was cut or is nonexistent there so if I do remove everything I am wondering how to proceed in areas where studs are missing. The thickness of a new floor would be three inches plus so my questin is can I use layers of 3/4 inch plywood or cement backerboard to build back up to the original level of the floor? Any ideas appreciated. Thanks,