First Time Plasterer Seeking Advice

Discussion in 'Other Trades Talk' started by AndyF55, Feb 26, 2014.

  1. BuilderMCR

    BuilderMCR Active Member

    I don't agree with these 2 day courses when people go on them and think they're plasterers and get a sign written van etc. but if your going to be skimming a fair bit in your house maybe try finding one local to you just to pick up a few of the basics.
  2. Hmmm, sorry to disagree, MCR ('cos you know I love you dearly...) but I think that might not be quite right.

    The PVA is mainly there to 'even out' the surface, so it's all equal in the sticky-stakes. And, yes, to seal any areas of old plaster that would suck all the moisture from the new mix. After PVA-ing, the whole area should be evenly ready for the new skim coat, and the PVA itself is a building adhesive so helps to bond the new skim on.

    Once coated, even a single layer of PVA is going to pretty much stop any draw of moisture away from the new skim - and that's part of its job. So, I really can't see it makes any difference if more coats have been applied - in this 'suction' respect at least.

    Perhaps 4 coats creates such a thick skin that is lifts as it 'reactivates'? Tho' it shouldn't.

    I have to say, following the first time I skimmed on to a tacky-dry PVA and the stuff turned into the slipperiest surface on earth - I genuinely could not spread the skim over it as it all just slid around in one splodge :eek: - I have always since then allowed the coat to fully dry. What then happens is the moisture in the new plaster 're-activates' the dry PVA surface, and it becomes just 'right' for skimming. Or perhaps it doesn't - but in any case the plaster goes on nicely as it should.

    Andy - test these areas with a screwdriver or summat. If they are clearly not attached to the substrate properly, then it'll need to be chipped/scraped off. If the surrounding area is fine, then you can patch just these bits. Dampen them well first, especially the immediately surrounding dry plaster.

    If, however, it's crazed but stuck firm, then I'd simply apply the mist coat of emulsion to the wall (say around 15% water in matt emulsion paint) and, when dry, apply a skim of filler over these parts, pressing it well in. The emulsion should have sorted most of the 'suction' problem, so the filler should go on nicely tho' it may need being made a bit runnier than usual.
  3. BuilderMCR

    BuilderMCR Active Member

  4. AndyF55

    AndyF55 New Member

    I did consider going on a weekend course, and I'm sure it'd be useful. However, this room is out of the way and not really causing us any bother so I'm happy to just keep practising until I get results that I can work with. I'm going to paper over the plaster - never done that before either - this is one big training exercise.

    Thanks yet again for all the responses and information.

    Right, over to the wall before it's time for pancakes.
  5. BuilderMCR

    BuilderMCR Active Member

    Pva is to control suction. I know an old guy who just uses water!!!!
  6. BuilderMCR

    BuilderMCR Active Member

    Is it pancake day?!? I'll have sugar and lemon on mine please, thanks!
  7. AndyF55

    AndyF55 New Member

    That "let me Google" service is ace!
  8. BuilderMCR

    BuilderMCR Active Member

    Just wondering DA... When you say to even out the surface, are you confusing bonding (as in bonding coat) with polybonding (as in pva-ing) lol
  9. How did you do that, MCR - I nearly carped myself as I started to type "why do you..." and looked up at the screen to see it typing for me. Bludy mind-reader Google :eek:.

    I agree with what you say; the PVA controls suction on surfaces that need it - old plaster, etc. As such, tho', a second coat won't make it even less sucky. And a third will make sod-all difference again.

    It's also used, tho', to provide a 'sticky' surface to surfaces that might not be so - part painted, etc. That's what I mean by 'even out' - an old wall needing skimming will likely be part skim plaster, part bonding coat plaster, part paint undercoat, part top coat part gawd knows what... A coat of PVA will make it all the same (even) as far as the new skim is concerned.

    All I'm saying here is, I don't think Andy's problem is too little suction due to 4 coats. It wouldn't matter at all if there was zero suction...
  10. BuilderMCR

    BuilderMCR Active Member

    Of course it would. It's like distemper. It's like skimming onto glass so when you start flattening off the plaster starts to tear. You need some suction. But not so much that it dries the plaster out.
  11. BuilderMCR

    BuilderMCR Active Member

  12. Suction? Really?

    I just don't see that 'some' element of 'suction' is needed for the skim to take. You could PVA a completely impervious surface just to provide adhesion, and it would still work fine.

    You saying that a coat of PVA allows 'just the right amount' of suction? What about when you apply PVA to a 'combination' surface - some bits bare plaster, some bonding, some paint? These surfaces have completely different suction rates, so surely - if what you say is right - the applied single coat of PVA would still have different amounts of suction on these parts?

    PVA has two jobbies here - one is certainly to cut down suction on really absorbent surfaces, the other is to provide adhesion. In which case one coat, two coats, three coats... don't really matter.
  13. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    I would imagine that 3 or 4 coats of PVA would turn into a slimy oil-slick once wet plaster is applied(unless it has been allowed to dry/cure for a couple of days), and when the PVA dries and shrinks, I would imagine it tearing the plaster apart!
    The normal advice also, is to wait for the PVA(second coat) to go tacky, means that it has already shrunk a tad before plaster is applied.

    Mr. HandyAndy - Really
  14. BuilderMCR

    BuilderMCR Active Member

  15. BuilderMCR

    BuilderMCR Active Member

    In plastering pva is used as a sealer, not an adhesive!
  16. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Then why is it recommended to plaster onto tacky second coat?

    Mr. HandyAndy - Really
  17. joinerjohn1

    joinerjohn1 Screwfix Select

    Exactly. If you don't pva the wall, the skim coat will crack all over , as the dry backing drags all of the moisture out of the skim coat.
  18. BuilderMCR

    BuilderMCR Active Member

    So, if pva is used as an adhesive why don't you use pva when you float and set in the same day?!?
  19. BuilderMCR

    BuilderMCR Active Member

    Why don't you use pva on plasterboards? Is the paper made out of pva? No the reason is because it's a low suction background so doesn't need sealing to control suction.

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