I've just bought a new house and found that the floorboards at ground level have signs of woodworm but only the underside, the top of the floorboards have no signs of any holes. I've removed some of the really bad boards and the rest seem to be strong enough so I've left them. Whats the best course of action? A diy manual states that I have to inject the holes every 3-4 inches but this will take forever! Can I just spray or brush it on the whole floor or will I have to remove the floorboards to coat the underside too? I assume I will have to treat the joists too? Lastly whats the best stuff to use. Any advice would be appreciated.