can I lay ceramic tile directly on ceramic tile?

Answer 1

Yes, but there are all sorts of consequences.
--by the time you lay the mastic and tile, you will have raised the level of the tile 3/8"-1/2" in height, so doors may not open.
--if the original tile has any loose pieces, the new tile will not have a solid base and will be prone to cracking.
--it will be a real trick to get the mastic base for the new tile to stick to the old slick tile, you will need to scuff it with a power sander.
Bottom line, for the effort and expense to do a poor job, you might as well remove the old tile and do the job properly.

Answer 2

Yes, but don't use mastic. Mastic will never dry when used over a glazed ceramic tile. You need to use a high-performance, rapid setting mortar or even an epoxy based mortar. I don't recommend the epoxy unless you are very competent. It can make a terrible mess. Of course you need to make sure that there are no loose tiles beneath, and that your finished floor isn't too high. If you use the right product and give adequate time for it to dry...(glazed tile is less porous than other surfaces and therefor the mortar will take an extra day to cure before you can grout), you will be fine.

Answer 3

I wouldn't advise it. After you finish and grout it. The grout may crack after a week or two.