Skimming over old plaster......

Discussion in 'Other Trades Talk' started by Skimming over old plaster, Jul 11, 2008.

  1. Hello all, i'm new here and am after a bit of advice.

    I'm looking at skimming some walls which have old plaster on them, I've had a guy check it out and he confirmed what I thought in that the walls are pretty solid and skimming will be ok.

    My question is what do I need to do to the walls before they are skimmed, bearing in mind the walls have been recently stripped of wallpaper.

  2. beefy 2

    beefy 2 New Member

    PVA 5:1 let it dry then PVA 3:1 start skimming when its tacky
  3. Would I need to wash them first with a sugar solution to get rip of any adhesive that may still be remaining as the walls feel quite rough to the touch?
  4. Tony Soprano

    Tony Soprano New Member

    a good prep is the most important thing when skimming walls,make sure they are cleaned down properly.

    specially silly niggly bits of wallpaper which may drag under your trowel and ruin that all important finish

    if the walls look like they will be very porous then u can do two coats of PVA.first one on and let it dry out totally .

    The second coat i wud put on just before you start to skim and allow it to go tacky before applying the multi-finish.

    Make sure to do two coats for a good finish
  5. cheers guys, thanks for the help
  6. nickthebubble

    nickthebubble New Member

    defo 2 coats pva as the other guys have mentioned... let the first go off... get rid of as much paper off the wall as you can... every little helps...
  7. Moto Slug

    Moto Slug New Member

    What you need is Thistle Bondit, its an adhesive/sealer and is painted onto existing sound walls, it like painting with emulsion but its got a gritty/ sandy texture to it, allow it to dry and the simply skim over, its about £60 £70 per bucket, not cheap but far better than any PVA.
  8. nickthebubble

    nickthebubble New Member

  9. Moto Slug

    Moto Slug New Member

    Yes thats the stuff, its much easier and better than any PVA, also tools can be washed out in water.
  10. devil's advocate

    devil's advocate New Member

    Hi soop.

    I guess you've done the job now? If so, what did you do,and how did it go?

    If you haven't...

    I have found that any traces of old wall paper paste can be an absolute swine as it re-activates when anything water-based is applied to it - emulsion, PVA, etc - and it expands and can make your job a mess.

    Certainly before painting, you'll have to thoroughly remove all traces - you might get away with it if PVA-ing instead, but it's a risk.

    On really bad walls (I think 60's-70's paste must be particularly yucky stuff), I've had to spray a little water on to the walls, allow it to soak into the paste, and then scrape them down using a squeegee. Followed off with a good wash down using sugar soap.

    I'm sure the Thistle Bondit mentioned above is great stuff, but you should get away with PVA if you want to go that way.

    Ok, are you a DIYer? Do you just want to be able to carry out the odd bit of skimming for yourself, or do you want to learn to do it like a pro? If the answers are 'yes', and 'odd bit', then read on...

    Apply the PVA as described above - the first coat slightly thinned (read the instructions), and when fully dry, apply the second. The second coat can be pretty much neat, or thinned very slightly if it makes it easier to apply.

    Ok, here's the easy bit - let it dry fully. Honestly. If you try to skim over still-wet PVA, then you'll find out why it's not a good idea (troweling on oil comes to mind). Ok, I know it's meant to be tacky, but if you get it even slightly wrong, you'll be very unhappy.

    When you let it dry, it becomes a superb surface to skim on to. The very top surface of the PVA re-activates slightly, and the skim bonds beautifully. Use a good, known brand of PVA, and don't use waterproof type.

    Right, the next hint is a cardinal sin - but if you answered the two questions above like I would, then proceed as follows... Apply your skim in - gasp - one thin (2mm-ish) coat.

    Sod doing two coats - this was pure invention just so's pros could show-off; it has no benefit in reality - it's a mere ego trip for plasterers.*

    Applying a single 2mm skim onto a dry-PVA'd wall is a dream.


    You can, of course, ignore all that if you wish.

    *Ok, - only kidding about that, but hey...
  11. Moto Slug

    Moto Slug New Member

    I must comment on a part of Devils last post, in which you said.

    Sod doing two coats - this was pure invention just so's pros could show-off;

    Anyone who has skimmed on top of PVA or Thistle Bondit and has had trouble with the skim bubbling up as they are trowelling it up, will know its hard to get rid of the air bubbles, a sure way to stop this is to apply a float coat first, allow it to tack off and then apply a steel trowel coat around 40/50 minutes after the first coat, it always works for me.
    Its possible to get away with one coat on plasterboard but I rarely do as I find I get a better finish with two coats.
    Right, I am off to book a plane for my ego trip ! ! !
  12. devil's advocate

    devil's advocate New Member

    Ha ha, cheers, Moto Slug.

    (I did add I was only kidding... :))

    I fully appreciate there must be a good reason for two coats, as it'd be a hell of a lot of extra work for no gain otherwise!

    One coat will do me fine, tho', and I was suggesting it to 'soop' as an alternative to make his life easier, as I suspect he's a DIYer too...
  13. cosworth

    cosworth New Member

    ive never met a proffesional plasterer who plasters in 1 coat unless its a tiny area.
    i thinks you work hard as hell to get a finish in 1 coat and you must be scrubbing the plaster with a soaking brush to keep it smooth.
    appologies if your getting a spot on finish but im not converted.
    you must be 1 a million doing 1 coat.
  14. devil's advocate

    devil's advocate New Member

    Hi Cosworth.

    You are absolutely right on a number of counts! Yes, I do have to work hard as hell to get a good finish, and I practically drown the surface in water during the process (I use a hand sprayer...)

    I did only suggest this to the OP as a DIY-type way of doing it, and I'm not at all trying to say it's a better way - it clearly isn't.

    I did - once - try doing the 2-coat thing myself... Bear in mind I had to mix it up as well and lay it on, but I ended up with the bottom layer going off with a few high ridges on it which then completely messed up the top layer as I applied it :(

    But, like the OP, I had a tatty wall to do in a bedroom which had numerous different surfaces - bare concrete, paint, old plaster, etc., and after giving it two coats of PVA and allowing them both to dry, I applied a single thin coat of plaster and it went on like a dream.

    So, I was only suggesting it as a possible solution for a similar fellow in a similar situation.

    (With a little wind-up for the pros in the process ;))
  15. Major Mal Funxion

    Major Mal Funxion New Member

    I find that plastering is a lot like bricklaying, anyone can do it, but there is wrong way and a right way.

    I mean, i could have a go at hanging a door ( not that i would ) but it would probably close by it's self.

    I could try doing my own wiring, but the tv would probably turn off every time i boiled the kettle.

    Leave it to the pro's!

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