this is very acceptable , as long as the old tile are well adhered no cracks or loose tiles . lightly abrade the old tiles with sand paper , clean tiles with wet vac , wash floor with tsp , install new tiles . a good mortar such as flex bond would work great . no leveling required as posted be the floor wiz , the notch in the trowel ,assuming 1/4, will give you the height you need to install the new tiles .Assuming your floor is relativly flat... hope this helps,
I did tile over existing ceramic tile (washroom wall). I tried using sand paper on the old tile but it didn't scratch it at all. I ended up using a grinder to remove that gloss. I used "omnigrip" as the adhesive and it worked well (too much adhesive caused the tile to slide off).
One problem is 1 or 2 of the old tile were not level and it slightly pushed one of the new tile out.
Take a hard rubber ball(kids love these things) drop it on every tile and listen for a hollow sound. I will almost guarantee that you will run into a couple. This means the tiles are slightly seperating or are about to.
Plus, when the new adhesive cures, it can create surface tension that can pull up the old tile.
Yes it can be done, yes it has been done, you just may be fine. Just do some fine tune checking to make sure you are doing all you can to make sure all is well.