I had a job doing a kitchen ceiling that was artexed but not really thick artex. I Pva'd it 3 times and before I put a backing coat over I made sure that the PVA felt tacky. I mixed half carlite bonding and half multi finish and applied it to ceiling. The next day I went back to skim it. I Pva'd over backing coat before skimming. However one part of the ceiling there was a lump. I pushed it up with my trowel and realised that it was sagging and started peeling off back to the artex. What may have caused this? As I Pva'd it 3, times before applying backing coat.