Ceiling too wavy for scimming, such a thing?

[howser]

Is there a point when a ceiling is too wavy (ripply) to scim?

The plasterboard's are sound, no signs of them about to fall down or anything like that, just wavy, not from water damage, dont know why.

What to scim them without have to rip all the ceilings down. Or is it a case of, yes you can skim them but it will look c**p.

Thanks

 

[Alastairreid]

A bonding coat to straighten then skim.

 

[roughcaster]

As Alastair said, you could straighten it out with bonding coat and then skim.
Your ceiling is probably boarded with old, thin 9mm plasterboard, which "was" a standard way of doing it in the past, but the thin 9mm p/boards sagged over time due to the span of the joists, which is probably the cause of the problem you have.
Nowadays, thicker 12.5mm p/board is used on ceilings, so more or less eliminating sagging boards.
If the sagging is "really" bad, and you couldn't live with it, then the ultimate way to sort the problem would be to remove the old warped/sagging 9mm ceiling boards, and start again/re-board with a new 12.5mm ceiling. There would also be a limit to the thickness of bonding coat needed to flatten the "old ceiling".
You'd also need to prep the "old ceiling" well first, before thinking about plastering it, if you went down that route. So 2 ways there to think of.