Dried plaster and patches wher ethe paint won't stick, why??

Discussion in 'Painters' Talk' started by SevernSeas, Nov 6, 2017.

  1. SevernSeas

    SevernSeas New Member

    I've just had a wall plastered in my hallway, was done over 2 weeks ago. The old plaster (1933 ish) up from the floor for about 1 metre was hacked back to the brickwork. All was bone dry, the plasterer comes and levels the exposed brickwork surface with cement mix and then puts a coat over the whole wall.
    The various layers were left to dry out. Then the top coat of finishing plaster left to dry for 2 clear weeks and all seems to have gone that light pink colour, now time to paint.

    The plasterer said to use a 50:50 mix of matt emulsion with water, so that's what I did. All seemed to go well but I notice the are patches at the lower levels where the paint seems not to stick and I don't know why. The rest of the wall (upper above a metre) has covered quite well but for some reason I have these bald patches. Does anyone know what's cauing the problem and better still, how to get the paint to stick as it should.
    After the first coat of paint I did brush off some white crystals, which I assume are just natural salts coming out during the drying process.

    Is the problem, the plaster still hasn't dried properly?

    [​IMG] https://www.dropbox.com/s/n6mh7maliivmdxy/paint_plaster_blotching.jpg?dl=0[/IMG]

    [​IMG]
     
    Last edited: Nov 6, 2017
  2. KIAB

    KIAB Super Member

    Cement scratch coat can take longer to dry than 2 weeks,so a finishing coat of plaster might trap any moisture in.

    Over polishing plaster or adding pva to plaster can also cause problems with paint adhering.
     
  3. SevernSeas

    SevernSeas New Member

    I've had a few probs in editing my first post. The dropbox link should be a photo of the blotches, there is stong sunlight casting a line across the photo which might add confusion.

    Interesting, we did discuss PVA in the mix, I left that decision to the plasterer who seemed against the idea.
    As much as I would have liked a polished finish, alas I think that might have been beyond my plasterer's skill level.
     
  4. KIAB

    KIAB Super Member

    Pretty sure it's moisture still coming out, think a damp meter would confirm this.
    PVA in plaster is definitely a bad idea causes so much grief, no need for it, in my opinion.
     
  5. Astramax

    Astramax Super Member

    As KIAB has already suggested, no doubt about it not being fully dry at all yet at the lower levels. Use a dehumidifier to accelerate the drying process. Did you use a non vinyl paint?
     
  6. KIAB

    KIAB Super Member

    If brickwork was damp,it can take several months to fully dry out, longer in the winter months, before it's fit for scratch coat or plaster,
     
  7. SevernSeas

    SevernSeas New Member

    Thanks for your info, seems like I just need to sit tight and wait. I'll try the damp-meter test. My plasterer warned me not to use vinyl, and indeed the underlying brickwork was bone dry.
    When I've worked on new-build housing, I've seen it where the site manager would hire in dehumidifiers post plastering.
     
  8. KIAB

    KIAB Super Member

    Bricks might appear dry on the surface, but underneath they can be far from dry, some bricks each one can hold up to ¾ litre of water.
     
  9. CGN

    CGN Screwfix Select

    You ideally dont want a polished finish..not good for painting!
     

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