The ceiling had a crack in it running down the centre, on inspection we found that 5 of the joists had come out of their slots allowing the ceiling to drop. So I drilled holes through each joist just above the laths, inserted a 10mm bolt to which I attached a garden wire tensioner, I attached the other end to a bracket bolted to the beam. Then I was very pleased to see that I could lift the ceiling the required amount just by turning the tensioners by hand a half turn each. This brought the ceiling up and secured it for the future. Now the decorator can fill the crack and repaint.  If this hadn’t been done gradually more strain and movement would have brought the ceiling down or at least damaged it beyond a simple two hour repair.