Ive recently had a room skimmed, and have just put the first mistcoat on.
When the skim was done i noticed a line of dark "stains" across the ceiling.. I painted over them and within a day they are showing through the paint.
The only thing i can think of is this is remnants of a water leak i had a couple of years back from the radiator above, and i think the line is level with a joist so maybe some kind of mould.
I have seen mention of using some zinsser paint to cover these, but am unsure of which one is best suited for the job.. theres still at least one more coat of paint to go on the ceiling before the finishing coat so maybe one of the sprays would work best.
Edit: attached a pic - not great but should give an idea of what it looks like
When the skim was done i noticed a line of dark "stains" across the ceiling.. I painted over them and within a day they are showing through the paint.
The only thing i can think of is this is remnants of a water leak i had a couple of years back from the radiator above, and i think the line is level with a joist so maybe some kind of mould.
I have seen mention of using some zinsser paint to cover these, but am unsure of which one is best suited for the job.. theres still at least one more coat of paint to go on the ceiling before the finishing coat so maybe one of the sprays would work best.
Edit: attached a pic - not great but should give an idea of what it looks like