What caused this?

[UnderCroft]

New stud walls put up in July. Decorated in November. Didn't finish off the skirting because they had to move on to a new job (wall prep work took longer than expected). Floor resanded after walls painted with an old fashioned noisy heavy sanding machine. Skirting had to be removed as there was a fault with the flooring that couldn't be removed by sanding. Skirting is now back on.

I've taken photos of the walls. The paint starting peeling after the sanding and before the skirting was removed. When the skirting was removed and put back on again this is what it looks like. Also found cracking vertically in 3 places in the new stud walls.

Can anyone tell me what ultimately has caused the poor paint finish? The paint is literally peeling off the walls/peelable in places where it's loose.

a) did we get the plaster painted too soon? (August finished plaster, November painting)
b) did the painters not prep the walls properly for paint on new plaster?
c) did the floor sanding shake the new walls to the extent it damaged the paint where it joined the skirting?
d) should I have waited until the flooring was finished before painting the walls? (Flooring was 'finished' but had to be redone due to fault)
e) or something else?

The decorating was arranged by me separately to the sanding and flooring which was organised by the builder who built the stud walls. His quality of work has been excellent but ultimately we're left with an expensive paint job and every single wall needs redoing. I only want to raise the problem with him if it's due to the flooring work. Does anyone know the usual reasons behind peeling paintwork? The decorator says it's because we didn't leave enough time for the job and they couldn't caulk the wall to the skirting (which would have had to have been redone anyway due to the flooring being taken up and some skirting had to be replaced). Any thoughts and advice welcome.

How many coats of paint did they put on?

They definitely did a white wash coat. And then a couple of proper white on top. Not sure if there was a third.

What puzzles me is that it doesn’t look like there’s anypaint left at all where it’s peeled off, I’d expect the first coat to have penetrated into the plaster so even if the top coats peeled that would remain.

Yes exactly. It literally all peels off to bare plaster.

Sounds like the first coat was not thin enough then to me.

It's the same on the feature wall which is a much darker colour. Peel back to bare plaster.

So the white wash thinned out coat to 'stick' the new paint to the wall hasn't done its job?

It’s a decorator issue I think. The removal of the skirting boards and sanding may have caused some touch up work needed, but that looks like they’ve just not sealed the plaster properly. Did the actually put a white wash coat on first? I’ve always done one v thin, one 50/50 and then two coats on top. With plenty of drying time in between

They did seem to (obviously I thought they knew what they were doing so didn't count accurately). They definitely did a sort of patchy white coat to start with. I'd probably say they did a 50/50 then 2 coats. Not 'v thin' from my memory.

Yes, I think so. I do similar to what hiding does. I’m guessing the first coat was too thick so didn’t penetrate the plaster as it should have.

@UnderCroft

So the white wash thinned out coat to 'stick' the new paint to the wall hasn't done its job?

Do you mean the mist coat? I’ve known people to make up the proportions wrong, but I wouldn’t expect a decorator to do that.

They were here for 5 days doing a couple of bedrooms too (2 coats on old paint).

It was peeling post floor sanding and pre skirting removal.

I sent a few photos post sanding pre skirting and got this response:

'It just wants a Stanley knife put along the top re caulked and touched in with the colour

If we were doing the entire job this is something we would have picked up on'

'Is that one of the rooms that the floors were re sanded
Has the vibrations or the sander knocked the wall?'

Mist coat yes that's what he called it!

If you pull on the paint that’s peeling off, what happens?

It keeps peeling until I chicken out and stop. Picture number 3 was me peeling and peeling and then getting scared at how much was coming off so easily.

Apologies. I haven't said thank you yet for taking the time to answer my very naive questions. Thank you. It really is appreciated.

What paint have they used? It almost looks like some kind of plastic Ive not seen paint come away from bare plaster like that before.

I had pretty much my whole house renovated about four years ago, the walls were all plasterboarded and skimmed. As soon as the plaster had dried I painted them myself, starting with a coat of cheap white emulsion (not watered down at all) then a couple of coats of B&Q Valspar in the final colour. Not one bit has peeled off, it all looks as good as new.

Actually, looking at your first and third pictures, there's quite a texture to the paint, it looks as though they put a really thick coat on. I used a roller, but my paint is pretty much flat, nothing like that. I did put thin coats on though.

It's happened in my house, but it was due to dampness (by the backdoor).

Definitely not damp as it's a lovely well insulated house with good ventilation (lived here for over a decade)

It's Johnson's trade paint. I gave him the colours and they colour matched it with Johnson's trade. He said it's the only one he used because he doesn't like having to do 4/5 coats with cheap paint. I have the tins so it's definitely that brand.

It was rollered. It does feel kind of plasticy on the bits I've peeled off. Kind of brittle but plasticy. I could easily pull that third picture strip up and up. But I stopped!

It looks like a problem with the mist coat. You shouldn't be able to see the colour of the plaster if the mist coat had been done correctly, because of the water to paint ratio, it should have soaked into the plaster.

Some do 1pt paint, 3pt water, but this can often be too runny and you'll see drip marks running down the wall.

My mum (decorator) does 1pt paint, 2pt water, and does two coats, and she also will never use silk on new plaster because of peeling.

@UnderCroft

They did seem to (obviously I thought they knew what they were doing so didn't count accurately). They definitely did a sort of patchy white coat to start with. I'd probably say they did a 50/50 then 2 coats. Not 'v thin' from my memory.

It looks like there isn't a proper mist coat.

50/50 should be fine for a mist coat using ordinary emulsion.

You left plenty enough drying time Aug to Nov.

I've Never seen it delaminate in whole sheets like that. I've got a room I suspect wasn't mist coated properly- but it's small flaky patches not the whole wall coming off in sheets like yours.

I wonder what paint they used to mist coat? Could it be bathroom paint rather than basic and the extra waterproofing product in it doesn't really work as a diluted mist coat?

They haven't done the mist coat. The should be basic contract Matt emulsion watered down. It mustn't be vinyl or you get the result you have.

They are not professional decorators to have done that. Is disgraceful. I had that in an old house and the previous occupant had done exactly that