PVA on new plastered walls and ceilings?

[lizziecupcakes]

Hi all, just a question about adding PVA to newly plastered walls and ceilings. I think most people on this forum would have probably tried their own plastering and then painted on it too with success, so I really trust your experiences and learnings.

I need to re-plaster my ceilings and add skim plaster to my walls. It will be gypsum plaster though . After, I intend to only paint my ceilings and walls (I will not want to use wallpaper on them).

The plasterer I am thinking of using is also a decorator (he has quite a big team who do different things). He has said that he will be adding PVA right at the end on the newly plastered walls and ceilings.

I did some reading online and, generally, the internet is recommending to not add PVA to the final plaster surface as this can cause paint to peel. I asked the plasterer about this and he very confidently told me not to listen to other people, he has been doing this a very long time, and he uses PVA to even out the surface and after it's dried I can do whatever I want with it, but it will need a mist coat too (with Leyland trade superflex emulsion for the mist coat). He was very polite about it. This plasterer has excellent reviews, both on Google and Which?. I believe Which? properly verify their reviews too.

Can anyone help me understand what is the proper way to do things? I would really love to add lime but I can't afford it right now and will look at it again when I do a whole house reno in 10 years (when we go into the loft conversion).

Thank you so much

 

[Cubist]

PVA and water solutions, there are other proprietary products available, are often used to stabilise 'old' plaster that has become a little/lot delicate. I've never known it to be used with new plaster unless there are sections where the new meets old. Personally speaking I'm not sure theres a good case for it even then.

 

[Cubist]

Its yet another sign of entropies effects I suppose that increasingly more often these days I find that elements of something I've heard or read that I don't understand or accept rattle around in my mind until some kind of order that makes sense to me emerges - and, I hope, to others too. If it doesn't I'm in more trouble than I thought.

A couple of years back having been disappointed by the design, dimensions, apparent build quality and in particular price, I decided to make a Toy Chest for my Granddaughters first Christmas. Wanting to make it attractive and interesting to her new eyes I decided to try my hand at some decoupage as a means to add some images she would recognise and enjoy - if its not a straight line don't ask me to do it - and perhaps also become a source of some embarrassment for her in later years. I mention this as 'decoupage' uses PVA or similar to provide an adhesive base upon which to fix a paper image to an object and the image is then coated with further layers of PVA that dries to form a transparent hard coating to protect it.

Putting this information together with your decorators recommended approach, and the contrasting views you discovered from other sources, has produced one of those 'Oh, now I get it' moments where a rationale that reconciles the differences materialises. I now think that it's all down to the degree to which the PVA is diluted prior to use. When used as a stabiliser for fragile plaster as I discussed earlier the PVA is heavily thinned with water which then operates as a transport medium to carry the PVA adhesive into the body of the plaster. When the PVA dries it creates new bonds between the plaster elements to re-fresh its strength and durability. For a newly plastered wall this would be superfluous as the newly made internal bonds between the plaster elements would be very strong. However, it could, depending on the degree to which it was diluted, in effect create a film over the surface of the plaster that would reduce the amount of, and or pace at which, fresh paint would be absorbed. Possibly then this may reduce the number of coats needed to achieve a uniform and satisfactory final finish. Also, if the PVA is not sufficiently diluted, the PVA film may become too strong to allow the paint to penetrate at all effectively - and this weakness could then manifest itself later as cracks in the paint finish.

And that's how I can contradict myself on the one hand but can square a circle of conflicting views on the other - too late for a life in the diplomatic corp thank goodness.

 

[fernicarry]

I also thought maybe something to do with making the new plaster less absorbent so that the paint gets a better chance to stick. But the same guy also recommended a mist coat which is standard practice for "normal" new plaster. Belt and braces? Snake oil? All tradespeople seem to have their secret sauce that they swear by.

 

[a twig]

I’ve only ever seen PVA put on new plaster when it’s going to be tiled.

I have vague memories of it being “a thing” years ago, but can’t remember why. PVA will slightly react with water when it gets wet so maybe the thought is it would help the mist coat to stick?? I can’t think why adding PVA would make the finishing smoother? Again guessing here.

Leyland trade superflex doesn’t exist, assuming he is meaning Super Leytex? Perhaps there are some magic additives in it that make it all work.

If he is doing the decorating then sure it’s his funeral, if I was in that situation and doing the decorating myself then I’d politely ask him not to.

 

[paulc]

I’ve only ever seen PVA put on new plaster when it’s going to be tiled.

And if you follow the advice of the adhesive manufacturers, they will tell you not to use PVA. An acrylic primer such as BAL APD is much better.

 

[Cherryburn]

The purpose of PVA while plastering is to limit how much water is sucked out by an old substrate you're plastering onto. If the wall is too porous it can suck the water straight out of your plaster and stop it from curing properly. Or at least it gives you a bit more time to work with it. But it goes behind your plaster, not on top of it.

 

[mardinor]

Makes no sense to use PVA.
A mist coat is deliberately diluted so it absorbs onto the fresh plaster, forming a strong bond. If you don't do this, the paint film sits on top and is more likely to risk patchy adhesion.
PVA will create a film. This may help the paint adhere to the PVA.
So they are polar opposite approaches - either may work but not both.

As others have said, I've only heard PVA used to even up bonding where gypsum is used to patch lime.

My advice: ditch the PVA and go with a mist coat.
Maybe call a few other decorators and ask them?

 

[lizziecupcakes]

Hi all, thanks for your comments and advice.

We decided to get more quotes.

One guy who cane round (very nice, seemed experienced) said he can remove the old ceiling plaster, then used metal ceiling things to add the plasterboard to the ceilings (this would apparently give a better finish because we want to preserve the original coving). He would then skim over this.

I asked how he would prepare it for paint. He said it doesn’t need anything. It’s apparently “multip-purpose” gypsum plaster that you can paint on to directly.

Regarding the walls, he said he can skim over it using some sort of PVA that’s applied to the old plaster and then he skims over that (helps it to adhere apparently especially for slightly crumbling plaster, which I have). He said it’ll need a few days to dry naturally. I asked how he’ll prepare the skimmed walls for painting and he said the same as above: It’s apparently “multip-purpose” gypsum plaster that you can paint on to directly.

Has anyone ever painted directly onto freshly plastered walls before? I am so worried about paint not sticking or peeling later.

@Lacan07 I wonder if you might have any advice and experience with this? Thank you

Thanks again everyone!

 

[Lacan07]

Hi all, thanks for your comments and advice.

We decided to get more quotes.

One guy who cane round (very nice, seemed experienced) said he can remove the old ceiling plaster, then used metal ceiling things to add the plasterboard to the ceilings (this would apparently give a better finish because we want to preserve the original coving). He would then skim over this.

I asked how he would prepare it for paint. He said it doesn’t need anything. It’s apparently “multip-purpose” gypsum plaster that you can paint on to directly.

Regarding the walls, he said he can skim over it using some sort of PVA that’s applied to the old plaster and then he skims over that (helps it to adhere apparently especially for slightly crumbling plaster, which I have). He said it’ll need a few days to dry naturally. I asked how he’ll prepare the skimmed walls for painting and he said the same as above: It’s apparently “multip-purpose” gypsum plaster that you can paint on to directly.

Has anyone ever painted directly onto freshly plastered walls before? I am so worried about paint not sticking or peeling later.

@Lacan07 I wonder if you might have any advice and experience with this? Thank you

Thanks again everyone!

When painting on to newly gypsum plastered walls you first apply whats called a 'mist coat', which is basically watered down white emulsion. This allows the paint to soak into the plaster and provide a base or key. You need to choose the right emulsion though, I can't quite remember which. Don't use the emulsions designed for very recently (still wet) plastered walls, this is usually specified for tradesmen who renovate quickly and can't afford to wait for the plaster to fully dry.

If you want to save confusion though some brands or outlets like Wickes produce an emulsion specially formulated for mist coats. Its costs a bit more but useful perhaps for peace of mind.

Some extra tips to help with adhesion:

1. lightly sand the wall prior to the first mist coat - You can buy sand paper and hand sander specifically formulated for gypsum plaster. I got mine in B&Q.

2. Ask your plasterer when applying his final finish to not polish so hard. They can adjust there finish, and less polish means better chance of the paint adhering to the wall.

 

[lizziecupcakes]

Thanks so much @Lacan07 !! When I apply the mist coat (I’m just going to buy it from b&q), do I add this when it’s fully dry or as it’s drying, or as soon as the plasterer is finished with polishing?

I don’t plan to paint for a few weeks later after the plastering is done because I have other jobs I wanted to do before getting to it, so just wondering if the mist coat must happen at a certain time in the plastering process?

Also, does it apply to the ceilings too?

Appreciate you so much!!

 

[Cherryburn]

It's not critical when it's done, as long as the plaster is actually dry enough when you start. Unpainted bare plaster will need a mist coat for proper adhesion whether it's been there for a few days or a few years.

 

[Lacan07]

Thanks so much @Lacan07 !! When I apply the mist coat (I’m just going to buy it from b&q), do I add this when it’s fully dry or as it’s drying, or as soon as the plasterer is finished with polishing?

I don’t plan to paint for a few weeks later after the plastering is done because I have other jobs I wanted to do before getting to it, so just wondering if the mist coat must happen at a certain time in the plastering process?

Also, does it apply to the ceilings too?

Appreciate you so much!!

Yes, it applies to all surfaces with bare gypsum plaster (the pink stuff).

Wait until the plaster is fully dry before applying the mist coat