Vinyl Matt emulsion blistering on contract matt base coat

Discussion in 'Painters' Talk' started by Dominic Bonney, Jul 21, 2020.

  1. Dominic Bonney

    Dominic Bonney New Member

    Hi there

    new to the forum but wanted to get some advice from all the painters out there. I’m a tiler by trade but been painting on and off for 10 years, including my own house which I’m working on now.

    After thoroughly prepping bedroom walls I gave everything a couple of coats of Leyland trade white contract matt as a base coat for a very pale colour I was getting mixed up. I actually changed my mind last minute and went with a dark colour. The problem is, once I painted my new vinyl emulsion on top of the leyland contract matt, small blisters started appearing and growing in size in various places. This didn’t happen on the first coat but it did on the 2nd.

    next day I scraped the blisters off and found that I could easily scrape my new colour completely off so very bad adhesion to the contract matt, almost a dusty/chalky surface behind it.

    I’d love to know if I’m doing this wrong or not. Is contract matt meant for overpainting with more durable vinyl matt like I have done, anyone else found trouble with paint sticking to the surface of contract matt? Been using the Leyland paint for years and never had this problem.

    Any form of help or advice would be greatly appreciated!! Thanks in advance
  2. Wayners

    Wayners Screwfix Select

    What was the top coat? Trade matt or dulux diamond matt. Some durables need a primer on anything pourus like contract matt...
  3. Dominic Bonney

    Dominic Bonney New Member

    Thanks for fast response. I used Johnstone’s vinyl matt emulsion on top of the Leyland contract matt. Ok that’s interesting, now you say that it makes sense that a primer is what that could need. Is there a primer you’d recommend for using as a base coat to top coat emulsions?
    Much appreciated
  4. Wayners

    Wayners Screwfix Select

    Layland acrylic primer undercoat works for me. Normally add water to help it along,then apply emulsion over. Most just water down the chosen emulsion as a mist coat then a full coat
  5. 2nd Measure

    2nd Measure New Member

    Digging up an old form here, but I know others like me refer to these forms a lot for answers, and this one touches on a common misunderstanding.

    tldr; watch this video (URL'd to timestamp):

    What *likely* happened, is that your paint blistered because the surface was not fully dry (I'm assuming it was new plaster/skim coat?) and the moisture - which could pass easily through the highly breathable, but very soft, contract matt, was trapped under the vinyl layers of your paint, causing it to bubble (or 'delaminate'). You just noticed it on the second layer, because it had longer to occur, and the extra layer further sealed the escaping moisture in.

    And the rubbing away was likely due to your painting over contract matt. Contract matt is designed *only* for use as a temporary coating for drying plaster (just to give it a little face lift), a role it can perform owing to it high breathability. Unfortunately this pretty nifty design leaves it chalky and even when dry it can be easily wiped away with a wet sponge. So any subsequent paint (with the sole exception of more contract matt) will not be able to properly adhere to the surface, rather it will just sit on the chalky residue waiting to peel off.

    AS a stranger on the internet, I don't know if this definitely was your issue, but your description matches this issue closely. In the future, I'd suggest waiting until the surface has *fully* dried (for fresh plaster a couple of weeks should do, just to be safe), and 3 layers of a vinyl paint (with the first mist layer being optionally watered down, no more than 20%). Or if you need to get it done in a hurry, use 3 layers of contract matt only, and let the next person deal with it when the surafce has fully dried.
  6. Liam McGregor

    Liam McGregor New Member

    I have used a contract matt as a mist coat, and the top coat of vinyl matt peeled and flaked in places.
    I have mist coated another room with the contract matt 3 mist coats, and its still chalky, i am hesitant to apply a top vinyl matt as i believe it will flake again.
    Should i apply the hardwering matt at 10% ontop of the contract as described in the vide around 14 minutes, before applying the top vinyl matt.
  7. Wayners

    Wayners Screwfix Select

    Watch video above
  8. quasar9

    quasar9 Screwfix Select

    You may have an issue with with the plaster being damp as said by 2nd measure . I have just done a whole house with Leyland contract Matt as a mist coat followed by Johnstone’s Covaplus Matt. No issues.
  9. Liam McGregor

    Liam McGregor New Member

    We did leave the plaster for 5 weeks and it was a pale pink. After 2 mist coats it was still a bit chalky to the touch could this be an issue.
  10. Wayners

    Wayners Screwfix Select

    With plaster either acrylic primer following application data sheet guide then on with retail paint (dulux with the dog on is retail)
    Retail paint has thixotropic tack added and can't be thinned or used as a mist coat.
    Use a trade paint that can be thinned and can be used to prime plaster if the application data sheet says so. Most can.

    Contract matt is for damp plaster that needs to continue to dry out over the coming months in new builds ect. Has no other use although many would disagree.

    Not being funny but just read the application data sheets. It's all there and will take 2 mins max as simple plan english and to the point. Paint technology is really moving on and different applications advise now with the many paints on the market vs 20 years ago
  11. Liam McGregor

    Liam McGregor New Member

    Thanks for your reply. We have colour mixed Leyland trade vinyl Matt. Which says on the tin "seal absorbent surfaces with a solution with up to 1 part water to 9 parts Leyland trade vinyl Matt" so are these the steps I should follow for new dry plaster walls. I read alot of posts never to use vinyl as a most coat.
  12. Wayners

    Wayners Screwfix Select

    Just follow these paint manufacturers guide. Only time not to is if you think surface has a problem the paint may not cope with, so then use a special primer.

    As for posts with different options just ignore and follow paint data sheet. Imo.

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