Skimming plasterboard again

[wrathkeg]

Hi. I need to do a small amount of repair work to skimmed plasterboard (not skimmed by me!). It seems like the previous skim has not adhered to the plasterboard really at all and comes off in large pieces. Is there anything I should do to help it adhere this time? Or just skim over the board again? The skim is over the grey side of the plasterboard, if that matters. It was done about 5 years ago.
Thanks,
wrathkeg

 

[roughcaster]

If it's as bad as you say, i'd remove all the skim if possible and start again, it'll give a far better job too, rather than patch bits here and there.
Once you're happy, give the wall a good brush/damp down, then coat the wall with diluted PVA to seal it. When it's dry, PVA it again and this time, plaster onto it while the pva is still wet/tacky. Never plaster onto dried out pva. You might get away with 2 coats of multi finish, or you might need to use a coat of bonding coat plaster first, then multi finish.
Check all the original tapes on the wall too, and if any are loose, remove them and re-tape any joints before plastering/skimming.
It shouldn't make much difference with the grey side showing. Years ago it did because of the way the the paper on the board was applied, but if you plaster it back the way i've explained, it'll be ok.

 

[wrathkeg]

Thanks for that: very helpful. I've used PVA before plastering before, just not over bare plasterboard.

The reason the plaster came off in the first place is that I finally got round to removing some UPVC trim applied when a new door was fitted, in preparation for redecorating. The plaster was sound (or at least it seemed to be) until I removed the trim. Although I was as careful as I could be when I removed the trim (cut the sealant with a knife etc) removing it made the plaster start coming away from the board. I'm pretty sure I have got all the loose stuff off, and the rest seems sound.

 

[skhudy]

I've read new plasterboard doesn't need pva, tbh I've never not used pva, I can't see what problems it would cause if you use it all the time prior to skimming aside from a little more time, I'd be interested to know if it did though!

 

[roughcaster]

That's right Skhudy, new plasterboard doesn't need to be pva'd at all. You can either tape or plaster/skim straight onto it.
But if you put up new plasterboard and then leave it for months and months, maybe years, then you will have to seal it with pva or similar, because over time, bare plasterboard will create a "high suction" and becomes difficult to skim because of it.
If you're going to skim over bare plasterboard that has been in place for a long time/months, maybe years, coat it with pva to seal it/kill the suction, let it dry, then, say the following day, the following week or whenever, pva it again and skim/plaster onto it right away, while the pva is still slightly wet/tacky.
If you're putting pva onto a light/white surface, mix some red food dye into the pva to turn it pink, so you can see where you are with the brush/roller.