Sanding plaster wall before painting

Discussion in 'Painters' Talk' started by Theleman, Dec 15, 2017.

  1. It looked glossy in your photos - at least as tho' it had a sheen.

    That's not good news - it isn't going to sand easily as you'd want. It quite possibly also didn't 'soak' in to the plaster surface which is what you want the mist coat to do. Hence it might be more prone to peeling and bubbling rather than sanding. :oops:
     
  2. Theleman

    Theleman Active Member

    Just read the label on the paint can. It says "SILK" emulsion. I asked my wife, why she got these, and she replied, because B&Q staff said that if you want to use final coat SILK, you must use SILK undercoat.
     
  3. Theleman

    Theleman Active Member

  4. KIAB

    KIAB Super Member

    :eek::rolleyes:

    So, bluddy annoying when diy sheds & some builder merchants,their staff don't know about the product they sell, or correct product to use/recommend, & treat females as thick.

    Had it other week, & the two oik's thought it so clever,to give a young lass with totally wrong info, I had to open my gob, been a hard day & I was in the mood for it.
     
    Last edited: Dec 19, 2017
    D4veNI likes this.
  5. Theleman

    Theleman Active Member

  6. KIAB

    KIAB Super Member

    [​IMG]

    Speaks a thousand works that photo.

    No need for stabilishing solution, go to have to strip it all off, as it will only peel off in time.
     
  7. Theleman

    Theleman Active Member

    So that SILK emulsion paint as undercoat have ruined the wall critically.
    I am furious at B&Q staff's advice, and them offering the SILK emulsion paint to my wife as undercoat paint.

    If not sanded, it seems solidly stuck on the wall. Taking all of them will be taking far too long.
     
  8. KIAB

    KIAB Super Member

    Silk emulsion just form a skin on the surface of the plaster, it doesn't soak in & seal the surface of the plaster like a mist coat of matt emulsion.

    She would have got the correct advice in The Paint Shed.
     
  9. Theleman

    Theleman Active Member

    yup, I should have checked it out. Just trusted all will be OK, but wasn't.
    SILK emulsion paints sounds totally useless product. Just forming a skin on the surface of the plaster? - who would want product like that, and why do they ever produce product like that? It bubbles and peels off. It is just waste of time, money and effort.
     
  10. Oh maaaan, Thele :(.

    Ok, the good news (there is some, honest...) is that once you actually paint your walls with MATT emulsion, it'll all look MILES better. Matt doesn't reflect light nearly as much, so small imperfections show up MUCH less.

    If most of the silk is well adhered, then just cross your fingers and good chance it'll stay in place. Try and run a scraper in to the exposed edges of the paint on that bare patch and see if the rest lifts or stays in place.

    Hopefully it kinda stays in place - 'cos the thought of removing all that is simply hellish.

    Do a test with that missing bit in your photo above. First you need to remove all raised or loose paint edges. Then get some MATT emulsion, pour a little ( a cup full) in to a tray and dilute it roughly 15% with water. Then use a short-pile roller to go over that patch - don't over-roll - and take it on to the surrounding silk painted area too. Allow to dry.

    See what it looks like. Hopefully all the old silk has stayed in place, and the bare plaster now has a neat (tho' thin) 'priming' coat.

    If so, now roll on a NEAT coat of the matt - again, don't over-roll. Ie - just apply, roll it out - blending in the overlaps - and then stop.

    Once dry, you should find that this matt emulsion WILL sand nicely and you can almost use it as a very fine filler - with a few coats you should be able to blend in - 'feather' - the ridge between the bare patch and the silk paint.

    If you find at any time that the silk paint either bubbles or lifts at the edges, then you're stuffed. Or even if the matt doesn't adhere well to the silk...

    In this case, the only other thing I can suggest is as KIAB (I think) said about Everbuild stabilising solution. This might just be able to rescue the situation by applying a sealing coat over everything.

    The stuff is very 'watery', so don;t overload the roller, but remove excess before use. Roll on - if runs form you have too much on the roller, so roll it out further... As always, don't over-roll - ie don't keep 'going over' the same areas.

    You simply want to apply a thin even coat - and then walk away! Allow to dry fully. If that all worked well (don't worry at this stage about any 'steps' in the surface from the missing paint layers or remaining ridges), then I'd be inclined to apply a second layer.

    If this works, you should - fingers crossed - be fine. The stabiliser should have formed a sealing, priming barrier.

    Now it's straight on to neat coats of matt emulsion (seriously - don't apply silk to any wall as it looks simply hellish...)

    Once you have had a neat coat of matt applied and all dry, stand back and go 'Phew...', because the chances are it'll look a LOT better than you feared (remember, matt hides imperfections...)

    Now it's simply a case of filling any remaining small dinks and dips, and also applying a smear of FINE filler along the edges of any missing paint areas - you are applying a bridge between the lower 'bare plaster' bits and the higher 'silk-painted' areas. Allow to dry, and gently sand with a flat block and 180 grit. You should be able to 'feather' the paint joins so they virtually disappear. Don't forget that matt emulsion itself is like a very fine filler, so if you add further coats over these areas - allowing each to dry fully - then it can be sanded back to do the job.

    Hellish situation, but good chance you'll rescue it.
     
    Theleman likes this.
  11. Theleman

    Theleman Active Member

    Great advice DA. Yup, taking it off at this stage will be hellish and will take about a year or two, so its out of question.

    I think I will just give another coat with Matt emulsion after filling and sanding. I think this happened in one of the rooms downstairs last year when painting. I am sure we have used the SILK nightmare emulsion at the time too, which were bubbling up. I recall keep taking them off, and repainting on it. But in the end, it got beaten , and I managed to apply second coat, which looks OK now. It is still there after that, the undercoat was not peeling anymore. But it was right down hassle. At the time, I was thinking we have some problem with dampness on the wall, but it is the SILK nightmare emulsion, which was the culprit.

    Thank you DA and all, very helpful and I learned a lot about this job - painting plastered wall.
     
    Deleted member 33931 likes this.
  12. KIAB

    KIAB Super Member

    A hot air gun will soften the vinyl paint enough to peel it off, just warm it, NOT so hot it blisters.
    Might also work with hot water.
     
  13. Theleman

    Theleman Active Member

    The area of the wall is just far too large as they extend to downstairs. Will take long time and effort.
    Maybe will speak to wife what she wants to do with it.
     
  14. DIYDave.

    DIYDave. Screwfix Select

    Not taking any pleasure in this latest twist re silk emulsion but I had said at least twice in my previous advice, ‘mist coat, plain non vinyl emuslion’

    Realise uv been given duff advice and the whole sorry tale has now got more problematic unfortunately

    Painting over the silk with matt can, as you have previously found out, can give more problems with the silk bubbling and lifting

    If your thinking of striping off the silk, try a wallpaper steamer and wide blade scraper, I’ve done this myself and it’s fairly slow going but does work. Your likely to end up with a few nicks in the plaster from the scraper but these can be simply filled and sanded - then mist coat ........ Again ;)

    Loads of suggestions above but if ur gonna leave the silk on and paint over, I would suggest that you seal it first with Zinsser Cover Stain, then 2 topcoats of your chosen Matt Emuslion....... your decision :mad:
     
  15. KIAB

    KIAB Super Member

    If he leaves vinyl on wall, it might come back to bite him days,weeks, months later, think it's better in the long term to remove it completely.
     
  16. DIYDave.

    DIYDave. Screwfix Select


    I’ve had this problem in the past of painting over silk with matt and it did bubble in several places - I remember asking the question on this site a few years ago and various options suggested (as expected) with a few people saying no problems painting matt over silk

    I think, and it’s only my diy opinion, that the problem is the silk forms a water tight barrier due to the vinyl in the paint. Matt paint has loads of water in its make up, and due to the silk paint, it takes ages to dry and sits on the silk for a long time, can’t be absorbed by the wall so dries totally by evaporation. It’s the water in the matt that whilst trying to dry, softens the silk and causes it to lift and bubble away from the plaster - strangely though not all over, just random bubbly patches

    I could be very wrong, just my non scientific thoughts, although have had nightmare experiences myself in previous house where several walls had been painted in silk

    The stain block (Cover Stain) being solvent based dries a lot quicker, again due to evaporation and chemicals and is totally different to matt emulsion. Should form a seal over the silk which will give a good base for future topcoats of matt emulsion whilst not reacting with the silk

    Stripped a silk painted wall a couple weeks ago for a mate with my wallpaper steamer and wide blade. Luckily just 1 wall, couple of hours sweat and it was all off. Light sand to remove few stubborn spots that were clinging on then a few knicks to fill

    Is messy though
    2 layers of dust sheets on floor then double layer of the thin poly sheeting. When done, just wrap up all the removed paint in the polythene and bin

    Anyway ....... where’s Astra ..... Xmas hols already ? :confused:
     
  17. KIAB

    KIAB Super Member

    Pretty much spot on.[​IMG]

    Worth the effort I think for peace of mind.
     
  18. Theleman

    Theleman Active Member

    Sorry DD, I was never in doubt about the paint emulsion. I was so certain the paint is OK, so didn't pay attention to your point at the time, I think.
    But we have wrong paint emulsion, now we found out. I was in distress, because it is a lot of work and time to even paint mist coat. Taking it off would be more painful work and taking more time. We wanted to do this work fairly quick before Xmas, but it looks it is not going to be possible, which is very disappointing.

    So to conclude SILK emulsion water based paint is not suitable for plastered walls, because they bubble up, whether undercoat or final coat. As I said in the previous post, we had experienced that in downstairs room painting, and was lot of hassle to finishing off the final coat, because the undercoat was bubbling up all the time. We thought it is dampness in the plastered wall, but it is the paint. This walls had been plastered months ago. It cannot be damp. It is bone dry, but yet the undercoat is bubbling up, and peels away.

    We were going to pick up the Titan shop vac last night but they closed at 8pm, and we missed the closing time by 5 minutes. I came home and watched the youtube reviews of the Titan shop vac, but wasn't too much impressed.

    I took out the old Vax small read vac, which was clogged up with plaster dust and lost suction. I opened it up, emptied the dust, and cleaned the filters, and put it back. It worked again, so vacuumed the remaining dust and debris on the stairs and corridor. Maybe this Vax vac will do? Or would it be still better to get the Titan shop vac?

    Wife says, don't take the SILK coat undercoating off, but just paint it over with Matt emulsion after filling and sanding, and then finish off with the final coat either Matt or SILK. If problem appears later, then work on it again. So that's what's going to be done.
     
  19. Theleman

    Theleman Active Member

    No, it is not going to work with the SILK emulsion coat peeling off.
    Must take off the paint with heat gun and putty knife, as KIAB suggested.
    A few days of lost labor and time. sigh.
     
  20. KIAB

    KIAB Super Member

    Hard work now, but end result will be worth it.[​IMG]
     
    Theleman likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice