Hi John.I had one of these a while ago to do. I think the hardest part is done and that is getting the tiles up without any real damage. I would use a stone polisher maybe around 240 grit on slow speed and gentle sand the addy down. Then check for any holes and screed over the holes with rapid. prime then tank and apply a 1mm fleece over and re tank immediately over the top (I used the mira tanking kit with there safecoat fleece from pure adhesion Harrogate).The tray is now repaired and fully tanked and ready to go. Do get one of those dust door protectors as the sanding will throw up some dust. If you need to borrow my sanding kit give us a ring or if nearby by i'll pop over and help out. though I am on holiday next week. Wet trays with thought to an exstent can be repaired Kevin