Any Decorators?

JtB

Black Lives Matter
Location
North Hampshire
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 uni-bond, used a good undercoat and no matter how many top coats we use the shadows always seem to return after a few years. Any idea what causes this and how it can be prevented?
 

Cuchilo

Prize winning member X2
Location
London
Paint the wall black :thanks:
 

screenman

Legendary Member
Unibond, could be the problem. Go over the wall with a oil based paint then emulsion if you want to. Or use Eggshell paint, which is oil based with a slight sheen to it.
 

Rafferty

Senior Member
Location
Essex
Polycell stain block will cover pretty much anything. It comes in a spray can. I've used it on water damaged ceilings where any paint will draw the stain through.
 

ayceejay

Guru
Location
Rural Quebec
Could it be that you are seeing efflorescence from the mortar between the blocks ?
If so this is difficult to deal with once the wall has been plastered over.
Not what you want to hear but either remove the plaster and clean the bare wall or cover it with plaster board.
 
OP
JtB

JtB

Black Lives Matter
Location
North Hampshire
Thanks for the suggestions.

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:
16881425472_d2c768d418_o.jpg

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

ayceejay

Guru
Location
Rural Quebec
East facing and outside wall? Once again I hate to increase your work load but perhaps the fix is outside before you attend to decorating.
 

Cuchilo

Prize winning member X2
Location
London
Thanks for the suggestions.

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:
16881425472_d2c768d418_o.jpg

It's odd because we have this on every east facing wall, but none of the others.
Why are you hanging a teddybear ?
 
OP
JtB

JtB

Black Lives Matter
Location
North Hampshire
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. Looks like there's insufficient insulation in the cavity. Seems this problem can be more noticeable in houses which are kept warmer due to a greater thermal difference between the cavity and room temperatures.

By the way, never noticed the teddy bear before - will ask the boss.
 

vernon

Harder than Ronnie Pickering
Location
Meanwood, Leeds
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.
Negotiate a wall dusting rota. That or use the lines as a template for a retro tribute mural of Manic Miner and similar ladders and platform games from the eighties.
 
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