I've been asked to finish tiling a friends bathroom, where the new ceramic tiles have just been stuck on top of the old (ceramic) tiles. I've not done this before, nor would I out of choice, but he's been left in the lurch so I've said I'll help out. I'm putting in a new wc and cistern, so will tile before I fit those.
Anything in particular to watch out for when tiling over existing tiles? Do I need a special tile cement (it's around/behind the wc in his bathroom).
Thanks for any advice.