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Long story short, this is the attempt that was made (not by me, so don't ask) at re-plastering a ceiling under uneven joists (natural sag, very old building). There's a mix of bonding and easifill 60 up there. How do I prepare this surface for multifinish? Also, do I need to skim the entire ceiling, or just the filled holes and plasterboard?

I am aware that there is a step where the plasterboard ends. I am planning on putting an LED strip profile there.

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    How nice do you want the ceiling to look after? Some people will go bonkers if there is a 1/8 inch bump in the ceiling/wall. The sagging ceiling joists should be checked carefully before adding more stuff/weight to them. Just because they are old, is not a good reason for sagging. Unlike people, wood usually does not become weaker with age.
    – crip659
    Nov 9, 2023 at 14:03
  • @crip659 I most certainly would not go bonkers with an 1/8inch bump. First time DIYer here so a few bumps is definitely budgeted for. Nov 9, 2023 at 14:09
  • As with most jobs, the prep is often the most important part. Make sure that the material your base you're trying to adhere the plaster to is solid, free of loose material, etc. If your new plaster doesn't have a good solid base, then it will be a big challenge to complete the job satisfactorily.
    – Milwrdfan
    Nov 9, 2023 at 14:47
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    I wonder if simply throwing up a layer of 1/4" drywall over (well, below) that whole ceiling would be the easy button...
    – Huesmann
    Nov 9, 2023 at 16:06

2 Answers 2

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No, it's not too rough. I've seen pros deal with far worse effectively. The key is to taper out far enough. You won't resolve this situation with an 8" knife, or even a 12". You want a 16" knife or larger, along with good technique. Don't expect to slather a bunch of mud up there and sand it flat. That doesn't work.

Give the current state a scrape with your knife before starting to remove small bumps and lines. Do that before starting each application.

Skimming the entire ceiling gets you a level 5 finish. That may be desirable, but with modern primers and paint coatings it may not be necessary.

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Given that one can plaster over a brick wall, hardly too rough.

But I'd say it's not very convincing as to soundness.

That hypothetical brick wall is a good solid substrate. The pictures here look like there's been some water damage unless it's just the terrible previous job - in any case, I doubt how well it will hold the new material.

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  • I'm not sure we see water damage. It could be a mix of product and paint coloration, based on the description.
    – isherwood
    Nov 9, 2023 at 16:58

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