Loft insulation

[5past6]

Hi folks we have installed 100 plus 170mm thick loft insulation in our newly converted annexe however the builder covered most of the soffit vents with it and we now have a mould on the black unbreathable roof membrane I have pulled most of the insulation back and loft now drying out will this White mould disappear in time or should I brush it off or use some sort of anti fungal paint over it any suggestions appreciated.

 

[Doggit]

Mould is normally black, so it may be salts that have come out of the plaster when it got wet, and it may just brush off. Post a picture please. But as it was caused by the builder, I'd be inclined to ask him to deal with the problem.