Ok, so i took them off but they were on their way. The walls were skimmed first, then PVA'd. I have read some articles for the process, some against, but anyway. After a few months, i finally got round to cleaning them, and found that the tiles were infact away from the wall. They were merely held in place by each other.
These are big tiles, about 9mm thick, and about 2ftx1ft in size. Porcelain.
'A friend' tiled the walls (in the Bathroom) and he has spotted them, each corner and the middle. The adhesive has come clean away from the wall, and i am having to chip the tiles clean before i re-use them.
Can anyone suggest why they came away from the wall, and what to do to ensure they stay on when i attempt to do them next time.
The wall is around the bath, not shower, so i dont think damping or wetness was an issue.
Any assistance would be greatly appreciated