http://www.diy.com/departments/gypro...g/35736_BQ.prd
Try that its very much like a good quality powder interior filler to sand once its properly dry but be warned its a pig to sand before hand, and 5mm depth takes 2 days to dry and that's inside on a plasterboard ceiling, not all smaller b&qs stock it I would mix a little PVA into the water too to help it stick and be less porous, I will be using it tomorrow I will do a test on something and stick it in the garage see how long it takes to set and if its up to the job. Ed/