Breeze Block Outline Appears Through Painted Wall

JtB

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All our inside walls are painted white and on the east facing side of the house you can see shadows in the paint which look like the breeze block outlines. We sealed the plaster with unibond, used a good undercoat and no matter how many top coats we apply the shadows always seem to return after a few years. Any idea what causes this and how it can be prevented?

It's difficult to see in the photo because it depends very much on how the light catches the wall, but here's what it looks like:
https://farm9.staticflickr.com/8747/16881425472_d2c768d418_o.jpg

It's odd because we have this on every east facing wall, but none of the others.
 
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JtB

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I did a bit of research and it looks like this is 'Pattern Staining' where very fine dust particles collect on the markedly cooler surfaces where the mortar acts as a thermal bridge between the cold cavity and the room. The cavities have insulation, but I guess the problem is that the sun doesn't ever reach the gap between our house the neighbour's to warm the wall, so not really sure what to do apart from repainting the walls every couple of years.
 
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Is a just painted wall of do you have lining paper up?
I'd call zinsser uk and see if they have a paint product that can overcome the issue failing that lining paper may work.
 
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Yep your second post i think is the reason. Is it possible to install insulated plasterboard ? I'd say if you line it you will probably have to use a thermal liner.
BTW by PVA ing it you've made things worse, unfortunately you've fallen victim to a common fallacy. Plenty of posts on here about it
 
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JtB

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Many thanks for the quick advice.

Just wondering if a less porous oil based paint would be better than an emulsion.
 

JtB

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Actually I'm beginning to doubt now whether the cavities actuall contain insulation or if it was just me that assumed they did because the house was built in 1993. This is something I need to investigate further because if the builder just used thermal breeze blocks and no cavity insulation then I can see how this problem would arrise.
 

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