What is happening to my paint?

[Silverbook]

Any ideas why the paint in my hall is bubbling like this? It was painted about 2 years ago. No damp etc.

A quick Google will tell you that's caused by heat or moisture lifting the paint off the wall surface

Why do you think there’s no damp? It surely looks like it. What happens if you pop the bubbles?

Jeez, this brings back horrendous memories … been there and learnt hard way after trying to paint my house white. Never had this problem before when decorating in previous 35 years.
this seems to be happening more and more with paints.

they are reducing pigments especially white pigment ( titanium dioxide) and replacing with other substances with less opacity - it means you need so much more paint to cover with same level of opacity
add to that almost all all paints are now water based and not solvent based - they take longer to dry, and are more easily absorbed into substrate ( what’s underneath)
So what happens is that you put first coat on, applying more than you should probably and then not waiting to dry. You then apply another coat and it doesn’t adhere to that first coat properly(the substrate in this case ) , moisture and air get underneath the layers and it start to bubble. As it dries it blisters and starts to take the other layer off too in worst case.
sometimes it can happen because the substrate is not properly prepared - a layer of grease will build up over years, or even just fine dust , or worse case the wall is slightly damp - all these will stop even first coat adhere it to the substrate ( old paint in this case)
Even if you do get it to dry , over next years it will blister and come off

so, it’s about preparation : always wash your walls thoroughly first with something like sugar soap and then dry thoroughly . If you’ve a lot of marks, or dark colour to cover use a primer coat first .

then apply paint thinly- if you’re going to use white or pal colour you’ll need a lot of coats, but avoid applying thickly . Apply thin. Allow each layer to dry thoroughly.

The on,y way to fix is, sadly, sole destroying.

leave it to dry thoroughly.
sAmd it down all over to remove paint or use a paint stripper. Take it back to its substrate
wash walls thoroughly - using something like sugar soap
leave to dry for a few days
apply a base coat if needs if walls are patchy or uneven - leave for 36 hours min
then apply paint in thin coats , leaving to dry for at least 24 hours in between- it’s not just about touch dry, you want all the water out
Build colour up slowly

and have a good cry, swear etc while you at it 😭😭

it may help to buy really good quality paint - these should have higher pigmentation. Frankly I vowed never to buy crown trade white emulation again though and Valspar paints, but I think it happens with all of them given right conditions

Sorry, I don’t have better news .

For causes, I agree with you. It could be remnants of wallpaper paste absorbing moisture- if so, that paste needs to be cleaned off- I wash/scour it off plaster with a kitchen scourer/sponge, using water with a bit of washing up liquid in it until a damp hand on the plaster feels no stickiness at all.

First coat on plaster is not just about applying it thinly, it's thinning the paint with water too (provided it is water based) according to the manufacturer's instructions for a 'mist coat'. Never ever use PVA for this- we used to be told to, but it's a bad idea.

Trade paint may need more thinning than consumer paint. But again, follow the instructions.
New plaster- you need to use something that will breathe- like contract matt- or claypaint- again, follow manufacturer's instructions as to whether the paint is suiable for nw plaster and the proportion of water for thinning the mist coat.

After that, basic rules for good, even coverage-
2 thin (as in thinly spread) coats are better than one thick one
Straight white will cover better than a colour, as there should be more titanium white in it
Better quality paint covers better, but more expensive doesn't always mean better quality.

If walls are lime plaster, and/or prone to damp, clay paint (or whitewash) will allow the wall/plaster to breathe and help it keep dry. Claypaints work better dampwise than modern vinyl paints, or wallpaper.

Yep, I do realise a mist coat is needed on raw plaster- I did say substrate and whatever that is. When I said apply first coat thinly, I was assuming she wasn’t back to raw plaster 🤷🏼‍♀️

I also disagree massively about straight white
ive painted rooms for last 40 years with all sorts of colours and had NEVER experienced this issue before. I then , moved into new place which had white emulsion on walls. I needed to redecorate as I was removing “feature “ walls and the white paint they’d done was extremely patchy - clearly slapped on badly over magnolia
this is when I experienced these issues - a complete fecking nightmare, 🤯

I know someone in the paint manufacturing business (theyre in industrial paint manufacturing though) and they explained about how titanium oxide levels were being reduced. We’re both chemists so not some random laymans opinion . They’re now using hydrous kaolin, synthetic silicates, calcium carbonates, talc, barium sulphate, and opaque polymer as substitutes or at least as partial substitutes, and this is why they are not as good coverage as they have to use a lot more of these substitutes to get a good opacity. Titanium dioxide is expensive and is also thought to be carcinogenic which means a whole raft of legislation has been bought in about milling size etc. for all sorts of reasons paint manufacturers are using alternatives.
Any paint of any other colour, has additional non white pigments - these create much better opacity by default . This is why I’d never had a problem at all previously - my off white /magnolia walls had yellow and variations of blue and red pigments sometimes, that all led to better coverage with less paint.
my issue was I used too much paint to get same opacity plus some of the walls were textured and therefore didn’t clean up properly after sugar soap wash.

I would never, ever, paint walls white again - I would use pale off whites, but never white.