Hello, i've had a wall re-skimmed by a different plaster to fix a poor job done by previous plasterers. This new plasterer scraped of all the cracked and blown skim and started. This time its a better job apart from one crack. However this hairline crack is straight over an old patch of putty that conceals plastic trunking housing an electrical cable. Could this cause a crack. The rest of his work is sound so can't be his work. Unlike last time cracks appeared everywhere and was hollow. Thanks. Phil