Tiling over old floor tiles

[mare]

I'm planning about renovating our bathroom (master bath in US terms).

Is it a Really Bad Idea (tm) to consider putting new floortile over the old tiles. The increase of height is not a problem since the current tile is actually lower than the hallway's hardwood floor. The current tile is flat, not cracked and seems stable to me. Removing it means a day of hard labour, a lot of extra bags that need to be brought to an ecological dump site, and generally more work to level the floor again with cement/thin set.

[DerbyDad03]

Have we Googled "tiling over tile"? For the most part it appears to be OK as long as you are sure the old tile is sound.

Layout seems to matter also - no new joints over old joints:

And there are cleaning instructions, special adhesives and mechanical abrading to consider:

[RicodJour]

Investigate isolation membranes aka anti-fracture membranes.

R