Hi all, have been asked to fit a Stovax Stockton 5 gas stove. Don't normally fit gas fires as a rule but this is for a lad i know. I have followed the MI's and fit a 5" flue liner already, ordered the fire and the adaptor from the steel flue to the liner, there is a lad there boarding all the walls and ceilings in fireboard and he is installing the fireboard in the chimney opening and has asked me to cut a 5" hole in and put my steel flue through this, he's an experienced dry liner and assures me the board is what he normally uses for this job, if it is correct do I need to put a fire seal in between the board and the flue or is an intumescent mastic fine for the job ???? Any advice welcome....Thanks in advance !!