Emulsion over mould stain on ceiling wallpaper

[simplesteve]

Hi guys, looking for a bit of advice on how to paint over a ( dry now) mould stain on the wallpaper of our bedroom ceiling ….
We had a leak caused by missing roof slates- now fixed and bone dry. I very stupidly wallpapered over the ( what I thought was dry) ceiling before it had dried out properly. All is dry now, and the paper is well stuck, but I’m left with a 12” dia mould stain on said new paper.
How do I emulsion over this ?
If I use an oil based stain blocker, can I go over that with emulsion ?
Thanks in advance ……

 

[opps]

There aren't many oil based stain blockers on the market these days.

My go to is the alcohol/shellac based Zinsser Bin. It dries really quickly. At this time of the year, you can paint over it about 30 minutes later.

Although it is white, it is an off white. You will probably need two coats of emulsion and because BIN will not let the water in the emulsion to soak into the paper, you will need to wait longer before applying the second coat of emulsion.

Do not use a foam based roller to apply the BIN, the alcohol breaks down the foam and makes it go floppy. A brush or non-foam roller will be fine. The paint is water thin, so use dust sheets.

Household ammonia will make the brush/roller look like new after using the BIN. It is alkali based and breaks the BIN down. You will be left with powder in the bottom of the tub. I use jars to store the ammonia. If you use an open container, the ammonia will evaporate off over night and you can pour it down the sink. There will be no residual ick in the sink.

Ammonia is smelly though. You may want to dip the brushes outdoors. If the brush has gone hard, the ammonia will still soften it.