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How to seal water staining on ceiling

i have water staining on friend’s ceiling which I have to paint. How do I seal the plaster, which seems solid, the stain just needs hiding. :smiley: Thanks guys.

stain block of choice. mines’s zinsser cover stain

Alkali resisting primer is the old and tried and tested way, it will seal back all damp stains dead, as long as the damp is no longer active. If the damp is active, they need a plumber or builder to sort the source of the damp or if there is no ongoing leak, wait till it is dried out.

I have bet my business twice on the fact the only water stains that APR will not seal is if the damp is still active.

One, I was asked by a client if I could seal the stain on her lounge ceiling. She’d had several “decorators” try and fail miserably and I was not as experienced as them but maybe I knew a way. I told her if the source of the damp was cured and the plaster was dry, I would decorate her lounge for nothing if the stain came through. She promised it had been dry for months. The sealer did its job.

And a second time, in a mansion in Wiltshire, we primer sealed all the ceilings as a matter of course. The plumber tried to haul me over the coals in front of the client, saying we had misled the client because there was a water stain on the ceiling right by the front door, so obviously we’d skipped on sealer. It didn’t look good, but I knew we had sealed it, and I politely told him he had a leak. That went down like a lead balloon!

He went absolutely nuts, and the client sided with the plumber because he had used him for years. It was a big old job at stake, and my name was mudd for an hour or so, and then, fair play to the plumber, he came and apologised. One of his guys had put a nail through a pipe when re-fixing the floorboard.

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Andy what alkali resisting primer would you recommend,thanks Dave i like some off your posts like Andy lot to be learned from both of you.

I have no particular favourite, the cheapest?

My understanding is that stain blockers like Cover Stain or ARP, will stop staining because the pigment doesn’t react with the alkali content in a dodgy substrate.

ARP deals with that one type of stain very well. I suspect Coverstain is formulated to resist a few more types of stain, which is why it is more popular (and a safe bet for more problems) compared to my suggested one trick pony.