I have just got a ceiling skimmed in a bedroom of a property I have just bought. The ceiling was very uneven (ie undulating and wavey). To make it smooth the plasterer has said he used 3 layers of skim and in some places he had to use 'quite a lot' (perhaps a couple of cms). I am now concerned whether he has put too much on and it may cause the the ceiling to become worse and even eventually fall down. Am I worrying unnecessarily and/or is there anything I could do to secure it (eg nails into the beams holding the plasterboard)? I think the plasterboard is 12.5mm and it is not clear why the ceiling was wavey in the first place.