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I've just had a skim coat of fresh plaster put on plasterboard (mixture of screwed to stud walls and dabbed on to brick/block) in a new extension and it appears to be drying very fast. Can I rely on it appearing uniformly dry to paint or should I wait longer in case there is moisture trapped that isn't visible?

FYI plasterboarding has been done over the last couple of weeks (multiple rooms).

(nb. using UK terminology here as that is where I am based - unsure if it is different for USA and things may be done differently there)

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    Usually surfaces dry out faster than the insides. Repainting a bad paint job is a pain, so I would wait. Not sure how many days.
    – crip659
    May 26, 2022 at 12:07
  • Are we talking actual plaster here or is it drywall with joint compound?
    – jwh20
    May 26, 2022 at 12:23
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    Thickest of the material matters most. Paper thin maybe a couple of hours or next day, about an inch(2.5cm) a week or more. Patience is a virtue.
    – crip659
    May 26, 2022 at 13:05
  • I think it is about 2-3mm over plasterboard
    – wizzardmr42
    May 26, 2022 at 13:52

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Ask your contractor[1] how long to wait before painting. He'll know best based on your local weather conditions and the thickness and type of plaster he used.

About the best the rest of us could tell you is "wait", "no, wait some more just to be safe".

[1] Assumption based upon the phrasing, "I've just had a skim coat of fresh plaster...". If OP had done it himself, one would expect something like, "I just put on a fresh coat of plaster..."

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  • Contractor said when it looks uniformly dry should be fine. A friend was skeptical about that, which was why I was asking
    – wizzardmr42
    May 26, 2022 at 13:57
  • If the contractor is a reputable guy/firm, I'd take his word. After all, if he's giving out bad advice that costs you a repaint or ruins the plaster job, he's on the hook for redoing plaster and you'll get all over social media to give bad reviews... Unless, of course, your skeptical friend has been doing plaster even longer, in which case, he would be able to give you a very definitive answer on when your plaster is dry. Probably wouldn't charge you more than a pint for his services, either.
    – FreeMan
    May 26, 2022 at 14:14
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Don't go by appearance. The surface might appear to be dry but the below surfaces can/will still be moist. Painting over it then will cause the paint to bubble/peel. If possible, get the information off the bag of plaster as to the complete drying time or contact the manufacturer.

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I've been in paint business for 21 years.

1 rule of thumb? If your guessing, you'll probably be wrong.

Regarding moisture content of any substrate, you can obtain a moisture meter to test it, be it wood, concrete, or plaster.

This is one we use at our paint store. There are less expensive ones and you can find them at any home center.

Technical Service Bulletin on moisture content and different substrates.

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