Preparing an old ceiling for decoration with emulsion paint

I want to prepare a ceiling for decoration with emulsion paint.
The ceiling is skimmed plasterboard. It has previously been painted with emulsion paint. Then it has had wallpaper pasted over it. Then it has had the wallpaper taken off, using a steam wallpaper stripper.
At present, the ceiling in general has over its surface a variable, thin film of wallpaper paste. Is it essential to remove by washing all the wallpaper paste before applying fresh emulsion paint, or will a slight film of wallpaper paste cause no problems for the emulsion paint?
Also, the steam wallpaper stripper has also removed irregular strips of the original emulsion paint, thus leaving very shallow depressions in the ceiling surface. The largest strip is around one metre long by five centimetres wide. What are good ways of dealing with this problem?
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Yes, it is essential, unless you don't mind a rather uneven texture and appearance. It's not hard to remove wallpaper paste - it's all water-based, so just get a decorator's sponge and sugar soap and you're in business.

The best way of dealing with both problems would be to line the ceiling and paint over that. When I was a decorator I tended to line all my jobs - you just get a much better finish that way. If you don't want to line it, I suggest getting some Red Devil OneTime filler and filling the shallow depressions. You might need to blind the filler as it tends to print through emulsion.
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wrote:

Yes, it is essential, unless you don't mind a rather uneven texture and appearance. It's not hard to remove wallpaper paste - it's all water-based, so just get a decorator's sponge and sugar soap and you're in business.

The best way of dealing with both problems would be to line the ceiling and paint over that. When I was a decorator I tended to line all my jobs - you just get a much better finish that way. If you don't want to line it, I suggest getting some Red Devil OneTime filler and filling the shallow depressions. You might need to blind the filler as it tends to print through emulsion.
Thank you for sharing your experience. What would be OK to use to blind the filler?
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[...]

I've used normal undercoat recently. Seemed to work ok.
Edward
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wrote:

OK. Thank you.
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