Just finished yesterday laying tile over tile in my 6'X6' bathroom. Came out great, going to grout today!

As long as the first layer of tile is firm without loose pieces, it is no problem. If the first layer is cracked or you can feel any movement in the floor, it is not a good idea.

Thank you,

Jane

If the prior tile has a high glaze you will have to deglaze the tile.

I agree. You need to "scarify" the tile with a sander or diamond cub wheel on a grinder. To install, you want a highly modified morter such as Mapai's Ultraflex II, available at Lowe's.

I think you have to check if the tiles are still firm and intact, if not just scrape the tiles before putting the new once. Just to make things make sure that it won't affect on the new ones.

Here is a link that might be useful: epoxy paint