Paint powder on new plaster

17 Nov 2010
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United Kingdom
Hi all

I recently had a local plasterer do some repairs to a wall in my utility room. The upper part of the wall was fine and didn't need any work - but the lower part needs to have some rough areas and channels repaired.

I asked the plasterer whether I needed to mist coat the new plaster before painting. He didn't think it was needed.

I painted the wall with a couple of coats of Dulux trade matt white emulsion a couple of weeks ago and now have a fair amount of dry white powder on the surface of most of the plastered areas.

I'm presuming that this is the result of not using a mist coat and that the moisture in the trade paint has been drawn in to the new plaster.

So, am not sure what to do now. I plan to put a silk final coat on sometime since the wife wants a colour on the wall. But I don't want to do that until I'm confident that I'm not going to be peeling the paint off at some time in the future.

Any thoughts appreciated.


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Its efflourescance (excuse the spelling).
Its not caused by the moisture being drawn into the plaster (thats whats supposed to happen) its the other way round.
Emulsion dries by forcing water to the surface and its drawn out the salts in the plaster. Its more likely to have been caused by painting the plaster before it was dry rather than not applying a mist coat.
It is essential to prime any new porous building/construction product, be it timber, plaster, filler, board, mdf etc. Your plasterer should have known better.

All you can do is brush off (do not wet) the efflouresance and paint as normal. Having not had a mist coat, the coating that you did apply may be a bit 'crispy', as it will have drawn in a lot of the water from the paint. You might get away with it though.
At least you didn't PVA it.
Thanks for the replies. Plasterer said to give it a week before painting.

After a week, I thought that there was still some more drying to do, since I hadn't got a unifrm colour. So I gave it another week before painting. I thought that would be ok, since I'd given it twice his recommendation.

Looks like that wasn't long enough? Should I use some salt neutraliser? Not sure if that would help?


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Even if such a thing exsists no. Don't think you've understood my reply, you will only get salt bleed on wet plaster, if its now dry there is no further chance of salts being pushed out to the surface. It can happen if the wall gets wet again.
There's no real set period for allowing plaster to dry as many things can effect it such as depth of plaster, exterior wall, cold weather, bonded first etc.
I think what you need to do is scrape and brush down the affected areas and if the skim is dry apply one coat of an Alkali Resisting Primer before you emulsion. This will ensure that when you apply your emulsion the moisture within it won't reactivate the salts.


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