Can I lay wall tiles over the old ones

If you want a proper job, take the old tiles out, remove the plasterboard and use instead cement board Hardie Backer. I know it is expensive solution but I guarantee that, if you use a good quality primer(not PVA) and adhesives, doing a good tiling, the result will be amazing. Thanks, Chris

Yes you can, with the correct adhesive as long as the tiles underneath are sound and flat we have done 100s of tile over tile bathroom installations and never had 1 callback

You can tile over the current tiles, please check the tiles are sound and not loose as this would cause problems later. Should they be loose, remove these and level the hole/gap to match the existing tiles, either with bonding/tile adhesive. For a better job, it is always better to remove the current tiles, however i would not recommend the removal if the wall is stud work with just plasterboard, as if they have been installed correctly you will find the plasterboard will come off with the tiles, this would then mean re-boarding the entire area.

It is possible too tile over tiles that are stuck flat and solid on stud walls cause you'll probably take the plaster boards off with it then you got two jobs too do on solid walls I tend too take off , use powder addisive for better use on the stud walls

I don't recommend you to tile over as the adeshive doesn't set up properly on the old tiles. If you do your bathroom I think the best choice is to take down all the tiles, plasterboard and redo it properly. What if the old plasterboard is damaged by any water leak? Most of builders recomand to tile over as is easy for them.

personally i would never tile over existing tiles (not good practice) that will just lead to complications down the line, especially when fitting a new bath or tray etc. always go back to the bare walls, if the walls need replastering or a good backer board then thats what needs to be done, But that will be an added expense.