I have around 60 bags of Thistle multi-finish plaster which expires 11-Nov. Plasterer is coming back on 1-Nov and I am not sure if he'll get round to using it all before expiry date (he needs to finish boarding up, skim the ceilings which will use some plaster but not all 60 bags), then float the walls before he can skim all them - chances are he''ll be at it until end of November. Is the plaster still likely to be OK if its week or two after expiry date? What is the deal with plaster expiry - I was told it'll set quickly when almost expired. Should I try and sell it off now or wait for the plasterer?