Skimming plaster over paint

awishawash

I've just finished chipping newish plaster off a bedroom. The plaster skim of around 5 mm didnt adhere to the old surface that was painted. I reckon it was on around 2 years. There was a bonding coat put on first from what I can see. I am wondering what the story is with painted surfaces. Surely no amount of PVA is gonna make a coat of plaster stick to it longterm?

AdrianR

Hard to know, you may have answered your own question there.

awishawash

Was just wondering if there was a trick to it or something. When people have their walls skimmed cos they have a few lumps or bumps what does a plasterer do thats so special?

Elfish

What kind of wall was it?

Was it the inside of an external wall of an old redbrick house with old lime plaster ?
Or was it a drylined wall with using plasterboard?
Or was the paint painted onto wallpaper which was covering very old plasterwork.

Could you figure out if the wall had been scratched for keying?
So, the question is, what kind of wall was originally painted? ie above questions......and what age is the house, and is the wall on the inside of an exterior wall or is it an interior wall?

Need more info!

Final question - where is RooferPete when u need him?:o Guessing still banned as no sign of him around :rolleyes:

You can skim over most painted surfaces provided you prepare it properly and that you don't have wallpaper. This is why most skimming is done in the first place though!

So you need to find out exactly whats under the paint........then can make decision.

Awishawash, i've found that plastering is one of the most deceptive trades ever, granted it looks easy, but takes years to master the subtle art of getting walls to a mirror finish. Which is why plasterers are now making funny money at their trade

awishawash

I agree elfish its very deceptive..but I must admit every time you go to do it your skills have improved.. Mainly the problem for me is usually getting the first coat even and plumb. I have skimmed over paint before a few months back and cant see any cracks or any hollow spots, but now I'm worried that in a few more the rot'll start. The wall where it was coming away was an old internal block wall, painted. The paint didnt come away, just the skimcoat. Maybe there was no pva used? Does it really make that big a difference.

Elfish

So it was an internal block wall which had been painted?
(So it was like the walls you see in schools or colleges - painted blockwork)

Not fully sure about this. I know that you cannot skim straight onto blockwork.
In the painted case as you have, again as far as I know, you need two coats of unibond before attempting to skim.

Next proper plasterer I meet I'll try find out. Often though, I find that all that younger plasterers know about is skimming onto plasterboard, and although they are perfect at that, their knowledge about the rest of the trade ain't the best....