Why is fresh paint cracking like this?

[uptoyou]

Hi, little background.
Around daughter's window was a lot of mold and paint coming away from wall.
Over the course of a few weeks:
Cleaned off mold with thinned bleach
Scraped the paint off, chipped away the loose (and maybe previously damp plaster). Some of this was coming away in 1" chips.
Scraped out all the old sealant and filled any voids going back into the wall with expanding foam.
Painted thin PVA coat onto areas chipped away and were to be filled.
Filled areas and leveled with Tuopret interior filler (max thickness may 1mm - 2mm but most maybe less than that even).
Sanded and mist coated the filler once dried.
1 coat of Zinsser mold-resistant paint.
Once dried lots of areas of where the filled areas had paint chipping away and flaking off the wall.
Scraped off, sanded, coat of emulsion (I was paint the ceiling at the time too)
Looked to be 'OK'
Went back over with the Zinsser and the same thing is happening again - although to a lesser extreme as previous.
Any advice please - pics below:

 

[opps]

I don't see that you did anything wrong per se.

You didn't need to pva the areas though. The toupret will stick to plaster, and although I tend to use the interior TX110 rather than the regular interior filler, it (the Tx110) doesn't need a mist coat.

Is the area subject to condensation? You mentioned that there was mould- that is common with a lack of airflow (cold bridges, no airflow when curtains are closed/etc). I does look like the emulsion has failed rather than your filler. Which emulsion did you use?

Although a PITA, you could repeat the process and tape a bit of silver foil over part of the area. If the bit under the foil is sound weeks later, it will suggest that the paint is pants.

 

[uptoyou]

Thanks opps.
This window does get a lot of condensation. The seal blew last year so prior to decorating I replaced the whole double glazed pane.
The wall did have a lot of mold and the plaster (trying to recall), may have been a little soft in places due to the mold/damp. I ensured the best I could that the area had dried out before working on it.
I posted a previous thread asking for advice here >>> https://www.diynot.com/diy/threads/...s-damp-areas-some-daylight-to-outside.605840/
Crown Matt Emulsion I used is probably a year old or so old, but not much was used first time round and I mixed with a drill and 'whisk' attachment before using.
I'm going to scrape the paint off in this area again (it's not as bad as first time round), and prep again.
I could try a different emulsion but I think this looked ok before I applied the Zinsser.
What is the reason for the foil and waiting for a couple of weeks - when I paint the Zinserr on the flaking is happening within the following day!

 

[opps]

Thanks opps.
This window does get a lot of condensation. The seal blew last year so prior to decorating I replaced the whole double glazed pane.
The wall did have a lot of mold and the plaster (trying to recall), may have been a little soft in places due to the mold/damp. I ensured the best I could that the area had dried out before working on it.
I posted a previous thread asking for advice here >>> https://www.diynot.com/diy/threads/...s-damp-areas-some-daylight-to-outside.605840/
Crown Matt Emulsion I used is probably a year old or so old, but not much was used first time round and I mixed with a drill and 'whisk' attachment before using.
I'm going to scrape the paint off in this area again (it's not as bad as first time round), and prep again.
I could try a different emulsion but I think this looked ok before I applied the Zinsser.
What is the reason for the foil and waiting for a couple of weeks - when I paint the Zinserr on the flaking is happening within the following day!

If the issue is down to condensation, the bit under the aluminium foil should be Ok- given that the moisture cannot pass it. It is a pretty blunt metric but it works (in most but not all cases).

The seal blowing probably makes little difference though. I think that is coincidental.

I honestly think that air flow is likely to be the main issue.

Based on what you have said, I do not think your product choices are at fault. You could use water based eggshell. Had you done so, the water may have just run off the walls and down the floor.

Airflow.. Sorry, probably not you want to hear given the cost of heating. Let air in, let air our, and you wont have mould. Close the curtains each evening- trapped (moist) airflow.

If you have trickle vents, open then, by doing so you are letting out the moisture heavy air. Alternatively fit a dehumidifying unit-

 

[uptoyou]

Yep, used to be a wooden drawstring blind which was never fully opened with the window staying shut.

Flaking got worse by the next day. Tried to scrape it all off again (but seriously, not easy scraping paint off a wall where only some of it has flaked). Ruining a lot of hard work, but it is what it is!



Painted over with just emulsion this time so I'll see how a a couple of coats of that works as a base before trying the Zinsser again.

Incidentally, gave the walls a first white coat today - this doesn't look ideal, possible cold patches from the outside?

 

[opps]

Yep, used to be a wooden drawstring blind which was never fully opened with the window staying shut.

Flaking got worse by the next day. Tried to scrape it all off again (but seriously, not easy scraping paint off a wall where only some of it has flaked). Ruining a lot of hard work, but it is what it is!

View attachment 300274

Painted over with just emulsion this time so I'll see how a a couple of coats of that works as a base before trying the Zinsser again.

Incidentally, gave the walls a first white coat today - this doesn't look ideal, possible cold patches from the outside?

View attachment 300275 View attachment 300276

It looks like it might be dot and dab plasterboard. The dark spots being where the dots are. To be honest, I have never come across that. The closest I have witnessed is unheated mirrors in bathrooms. When the steam starts to build up, it sometimes becomes more obvious where the lines or dabs of mirror adhesive are.