There is a slight bit of mould caused by condensation in my bathroom, around the top of the window frame. I suspect it's from before the double-glazing was installed a couple of years ago, as it hasn't got any worse in the 10 months I've lived in the flat. Anyway, I'm about the have the bathroom done, and the bit where the mould is will be skimmed and re-painted, not tiled. Should I treat this with something before it is skimmed by the plasterer, or can I simply wash it off and it will go away? I'm worried that it might seep through the skim layer and the paint....