I own a house with a concrete slab foundation. In my kitchen, the floor is presently covered with vinyl sheet flooring (as opposed to vinyl tiles). The floor is not is good condition and has been there since the house was constructed in 1981. I want to install a ceramic or porcelan tile floor using tiles from 12 to 20 inches square. Do I need to remove the old vinyl floor first or can I install the ceramic or porcelan tiles over the vinyl floor withour removing it? If the answer is yes, is there any type of special preparation that is required to get the vinyl floor ready to act as the base for the tiles or is there any special method for installing the tiles over the vinyl floor?