Tiling on top of tiles

It is always preferred to remove old tiles but not totally necessary with modern adhesive look for one specific to that purpose and the correct notch of trowel and as long as there was no obvious signs of movement, cracking ect it would be fine without putting down an uncoupling layer.

This can depend... Normally, I would say no. Tiling on top of tiles is not good practice. However, if the floor has old quarry that are solid then you can use a primer on the floor, self level it with latex then the floor should be good enough to tile. Remember it's better practice to remove the tiles but some of the older buildings that have solid orange quarry tiles are sufficient sub floors. I hope this helps. Kind regards Joe

I do agree with tiling over old tiles ONLY if the existing tiles are not moving , no cracks in the tiles or grout lines , there are no leaks etc. It is always recommended to remove them in case there are any issues behind them and in case of layering the tile , this should be done by a professional and it is always best to use a grip primer ( Eco Prim Grip Plus from Mapei) this will ensure the surface is as possible for the new tiles to adhere properly to the old ones Hope this helps!

Is best to remove old tiles and prepare the area properly and lay down new tiles