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What is the best way of fixing minor blemishes in new plaster before painting interior walls? In particular, should I sort them before or after mist coating?

Background:

I bought a 1930s house in the UK, with brick internal walls coated in old lime plaster and wallpapered, painted and wallpapered again (sometimes several times!). We wanted to freshen up and get to a good painted finish. After removing the layers of paint and paper, the original lime plaster was sound, but had a poor surface texture and carried a number of obvious scars from previous remodelling and electrical work, not to mention lots of holes where screws or rawlplugs have been removed. Hence we have decided to have the lot re-skimmed with new plaster, to give a smooth paintable surface.

The problem:

I know that normal paint tends not to stick to fresh plaster, and the advice is generally to apply one or two mist coats of watered-down emulsion before painting with top coat. I want the best possible surface finish, so I am also planning to lightly sand down the plaster to remove any drips and splashes, and apply filler to any small bubbles. Some brown blemishes have also appeared in the new plaster as it dried, which are probably due the remains of screws or nails embedded too deeply in the old wall to be able to extract. I know that these need to be sealed to stop the stain coming through to my new paint, and plan to do this with something like Zinsser B-I-N.

My question is: does my overall approach sound sensible for getting a smooth, blemish free painted surface? And if so, should I do the sanding, filling and sealing before the mist coat of paint, or after? Will the filler and sealant have adhesion issues if I haven't mist painted, or will the thin paint underneath make them less effective, or more likely to flake off over time?

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  • Get some primer it will stick and then you will use less paint in the long run.
    – Ed Beal
    May 18 at 19:35
  • What does your plasterer recommend for finish work prior to painting? He, more than anyone, should know what's required.
    – FreeMan
    May 19 at 13:43
  • "we have decided to have the lot re-skimmed with new plaster" - so you hired a plasterer? No good plasterer is going to leave it w/o a coat of primer. ... You have to put a coat of paint on bare plaster or drywall mud to see if you did it right. - Sand everything as optically flat as possible. Then apply primer that's made for the purpose. Then you hire painters or DiY.
    – Mazura
    Jun 18 at 0:36
  • Also, mist coat? A what? If you want no texture, use foam rollers. If all coats are going to be sprayed by painters, then there's really nothing for you to DiY in between the plasterer and the painters.
    – Mazura
    Jun 18 at 0:40

1 Answer 1

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Finish plaster should have a smooth, well-polished and highly consolidated surface. Sanding, even lightly, will ruin this and if the skim coat has been applied by a competent plasterer no preparation should be necessary (save perhaps carefully removing the odd trowel mark with a thin-bladed scraper). I have a similarly aged and constructed house and have found that Dulux Plaster Sealer works very well both on new finish plaster and on the old lime plaster finish. Apply the sealer direct to the new plaster and paint over it as normal, no further priming / misting required.

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