First of all a big shout out to everyone that contributes to these forums in terms of help and advice - I don't post often but I really appreciate the tips that I've been able to pick up here - if only I had the time and money to put more of them into practice! Right now I am having a go at re-tiling a guest bathroom and have a fairly basic problem to work on. As you can see from the pics, one wall is plaster skim over PB, the other is plaster over what looks like mortar. Where the skim has come away I am wondering if I can fill the holes and, if so, what with? Should I re-skim? I imagine another option might be to remove the old PB one one wall and re-fit, but there is a problem with this solution because we would like to keep the mirrors that seem to have been glued to the plaster (and if they are not glued, they have some very clever fixing system that I haven't been able to discover!) It's not a question of the work involved in re-boarding, I just don't think it would be possible to remove the mirrors without breaking them. Unfortunately we want to put a fairly heavy tile up (600x400 porcelain, about 10mm thick) so I am anxious to do everything as much as possible by the book. All advice greatly appreciated.