Newly skimmed walls/ceiling in bathroom - what primer?

[misterhelpful]

Tell me, what benefit do you think the non vinyl has over vinyl?

The issue with using vinyl emulsions for misting is that, even when diluted, bare/porous surfaces can still wick too much water from the paint which can then leave a paint film of vinyl which is more susceptible to peeling than non vinyl paints.

Pretty much every decorator here and on worksites all over the UK will agree that contract matt is the best option for mist coating but you are certainly entitled to your opinion and recommendation of vinyl emulsion. I will say that people don't post on here asking why their paint is peeling after applying contract matt whereas the number of threads that state they have vinyl emulsion peeling is countless.

These mist coating arguments get tedious after a while so I'll stop now and point any further readers to the thread I wrote on the matter a while back so that they can get a bit more detail:

//www.diynot.com/diy/threads/mist-coat-or-pva-bare-surface-basics.425261/

 

[joe-90]

You still haven't told me the benefit of contract over vinyl. Don't be a sheep. Use your intellect.

 

[dcdec]

When paint is applied to a wall it is a liquid. When dry its a solid. The binder forces the components (polymers i think) together and it film forms. Emulsion dries by forcing water to the surface and evaporating, but a bare plaster wall is too dry and the porosity of the plaster has to be satisfied otherwise it will suck all the liquid (water) out of the paint making it brittle and likely to peel or crack. This is why the first coat is thinned down. Vinyl paint when it film forms can prevent water in the plaster from escaping and can be seen in the form of 'bubbling'. This, as i understand it, is why non vinyl/contract matts are recommended for bare plaster. I've used vinyls as mist coats with no problem but there is a simpler much better reason for using contract emulsion. If i mist coat with LG intellimatt its gonna cost 3 or 4 times as much as a 'builders' contact matt and thats a considerable benefit. Never had a problem filling over contract but i always pole sand first. I agree that the first vinyl coat is stronger and more solid so i think the word sealer is slightly out of context as in many applications a sealer coat is regarded as protective. A mist coat only does one thing and thats satisfy/equalise the porosity of the wall. Secondary factors like show surface defects are a bonus but not the main point. If your filler is drying out or crumbling the wall is sucking the water out of the filler, this would lead me to think you are not thinning the first coat enough, the wall is still 'thirsty'. Filler is also more porous than your mist coated wall which is why we spot prime.

 

[joe-90]

Contract paint remains porous. I use it when I've been plastering to brighten up the room and check for defects. It also allows me to paint earlier as it isn't a sealant coat, so will allow the wall to dry. However, my first vinyl coat is thinned (mist coat) otherwise the non sealed wall will wick out the water and you risk pealing or a very bad case of roller stipple. Check the back of a tin of vinyl paint and see if it says "Not for mist coat, use contract paint for that." I bet it flippin' well doesn't.

 

[dcdec]

I think this is a pointless argument with a man who's sole purpose is to justify a skewed reasoning, and one who adapts his argument by changing industry standard terminology and practice without any authority other than opinion. You might be better joining the flat earth society Joe.

 

[joe-90]

It's written on the back of every tin of vinyl paint. You may not like it in your blinkered world - but it's true just the same. Get over it. Stop being a sheep preaching the same old, same old, that was preached to you. Use your intellect, man. Accept the world as it is - not as you think it is.

 

[mikeey84]

Could it be that contract is recommended, as if the plaster hasn't fully dried out it is still allowed to breathe and dry as mist coats are often applied to fresh plaster?

 

[misterhelpful]

Could it be that contract is recommended, as if the plaster hasn't fully dried out it is still allowed to breathe and dry as mist coats are often applied to fresh plaster?

That is one of the main advantages but you'd still have to wait for the moisture in the plaster to dry out before applying any vinyl paints over the contract matt.

As has been said previously in this thread, and countless others, Vinyl paints can be used to mist but they are not the best option. It basically boils down to the fact that, if the paint isn't thinned enough to satisfy the porosity of the substrate, vinyl emulsion will more than likely leave a paint film that is liable to flake and peel, especially when subsequent coats are added in the future. Contract paint, although sometimes powdery to the touch when dry, will not leave a film that peels and also allows moisture to still be absorbed into the substrate if the porosity hasn't been fully satisfied.

This is one topic that will never get 100% agreement but, experienced, professional decorators know the best products for the job.

 

[joe-90]

Yes. And that is vinyl. I've just explained where and why I use contract, but the first REAL mist coat is vinyl. Get over it. Dinosaurs aren't welcome.

 

[misterhelpful]

Rawwrrrr!