I'm filling in an internal doorway, stud frame with plasterboard. It's 204cm tall and 80cm wide. It's 13.5cm - 14cm deep, it varies, I've read I need about 3mm resess for the plasterer to skim.
B&Q does
C16 Stick timber (T)45mm (W)70mm (L)2400mm, this plus two layers 12.5mm board gives me 12cm...