Hi there, years ago (14+) my Dad retiled on top of existing tiles in my bathroom. There are now two tiles that have lifted - i actually pulled them off completing this morning. here i have lifted the tiles, the floor seems water tight - the water level in the recess hasn't moved in several hours. There is discolouration - mould as I noticed this issue a couple of months ago. I also have some missing grout in patches. I am after advice on how to prepare and re-stick the tiles, remove existing grout (where patches of it are missing) re-grout and whatever other steps remain. many thanks for the tips, Lou