We've had a leaky ceiling due to some problems with our roof which are now fixed. The plaster on the ceiling hasn't sagged but there was a wet patch that's made a big brown tide mark. There was also some black mould in the middle of the wet patch, which I've treated with Ronseal mould killer.
What are my next steps to getting the ceiling looking normal? I'm planning to leave it for a few weeks to let it dry out fully and go over the whole thing again with mould killer at least once. But then I'd like to make sure that the tide mark doesn't come back through any paint I go over it with. Should I be using a damp barrier undercoat or are the one-coat options actually any good?