Situation:
This floorboard is at the door entry to the shower room, I have just lifted the old tiles and that one had a crack, now I know why. I will be laying new tiles soon and the problem is that `plank` (t&g) is
4 inches wide and I will be laying 9mm ply on top of it, previously it was something like 5mm ply. I have access to one end of the plank but the other end could be hell knows how many feet away under a carpet with felt on top of wooden tiles, so not keen to lift any of that.Would the 9mm ply be enough to stiffen it or any ideas?