I am in the process of removing a redundant airing cupboard from the corner of one bedroom.Taking away the beeze block walls has left a gap in the ceiling so I am going to have to fit a new bit of plaster board about 70cm square. I have measured the thickness of the board used for the ceiling and it seems to be 17mm but in B&Q I can only find 9mm, Is
17mm available? or will I have to use two bits of 9mm and end up 1mm too thick?