Mainly the products i m talking about are considered to be cement backer boards for tile installation.
Cement over tile floor.
Cement board and fiber cement board.
Wonderboard durock and permabase.
Another and i think better way would be to use a self leveling concrete that can be aplied in a much thinner coat and if head room is a problem would be of help.
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Examples of cement board are.
If you were to use conventional concrete i would say you should pour a minimun of 3 inches both for strength and to ease leveling.
You most certainly can pour a new floor over your ceramic tile.