This was a GRP Fibreglass roof We fitted in Heald Green, Stockport. As with all GRP systems We install, the boarding We use is always OSB3 8×2 interlocking T&G boards, writing side upwards. We have been to quite a few GRP roofs that haven’t been installed no more than a couple of years, and already they have delaminated from the boards and move up and down when you walk along the roof surface. This is always down to the boarding used, and it is usually Marine ply or some other type of ply. Ply boards like this have a film of lacquer on them that the GRP liquid can’t adhere to. the boards need to be course and dry so the liquid can key into and then bond to.