Remodelling a small or large bathroom can often involve more work than meets the eye. 

Often when old tiles are removed, plaster or plasterboard can come away too, so walls will need to be reinstated.

Plasterboards in bath and shower areas will cause black mould and tiles to come away around bath and shower tray areas.
These should be replaced with more modern waterproof materials. 
All of these issues are dealt with and new materials are guaranteed to surpass building regulations.