Patches on external wall

FreeBear

jonnydeppiwish! said:

Have you used a decent stain cover paint before painting over it? Something like a Zinsser type should block it if it’s just a stain coming through. Be careful with it though - it’s very watery!

If it is cold spots forming because of dot'n'dab plasterboard, a stain blocker won't do much. The cold spots will still be there, and they will attract condensation..

But with a wall thickness of ~400mm, that would suggest a fairly new build with a (hopefully) well insulated cavity. So in theory, there shouldn't be any appreciable cold spots.

Anoneemoose

FreeBear said:

jonnydeppiwish! said:

Have you used a decent stain cover paint before painting over it? Something like a Zinsser type should block it if it’s just a stain coming through. Be careful with it though - it’s very watery!

If it is cold spots forming because of dot'n'dab plasterboard, a stain blocker won't do much. The cold spots will still be there, and they will attract condensation..

But with a wall thickness of ~400mm, that would suggest a fairly new build with a (hopefully) well insulated cavity. So in theory, there shouldn't be any appreciable cold spots.

Erm, I think it was built just after WWII. 😬 ~1948. I couldn’t see to measure properly so will double check in daylight, though I don’t think I was too much out. 

It was my husband’s grandma’s house before we bought it and I know she had some cavity wall insulation at some point when she was still alive and not too long before she died. I’m not sure exactly what that entailed though off the top of my head, I’d have to dig out the paperwork. 

stuart45

I would guess it would be a 10-11 inch wall if built just after the war. Should be reasonably well insulated if the cavity has been filled properly. 

FreeBear

Anoneemoose said:

FreeBear said:

jonnydeppiwish! said:

Have you used a decent stain cover paint before painting over it? Something like a Zinsser type should block it if it’s just a stain coming through. Be careful with it though - it’s very watery!

If it is cold spots forming because of dot'n'dab plasterboard, a stain blocker won't do much. The cold spots will still be there, and they will attract condensation..

But with a wall thickness of ~400mm, that would suggest a fairly new build with a (hopefully) well insulated cavity. So in theory, there shouldn't be any appreciable cold spots.

Erm, I think it was built just after WWII. 😬 ~1948. I couldn’t see to measure properly so will double check in daylight, though I don’t think I was too much out.

As built in 1948, the walls would have been lime plaster. Has that wall been renovated at any time ?

If it is indeed dot'n'dab, it will sound solid on the dark spots, and distinctly hollow elsewhere when tapped with a finger or knuckle.

Anoneemoose

@FreeBear - I thought it had only been skimmed with finish but some of the walls in some of  rooms have been back to brick (all internal walls are brick), plasterboarded and then skimmed over the top to finish. I didn’t think this was one of them though. It’s a mystery! 

These are some pictures of other bits of the house in various states of renovation, in case they help with the history.

stuart45

It looks to me very likely to be the dabs showing. People sometimes get this problem, without the marks appearing damp. It can be ghosting, where the dust gets attracted to slightly colder spots, often seen on ceiling joists, but sometimes higher up walls.

Anoneemoose

stuart45 said:

It looks to me very likely to be the dabs showing. People sometimes get this problem, without the marks appearing damp. It can be ghosting, where the dust gets attracted to slightly colder spots, often seen on ceiling joists, but sometimes higher up walls.

Thank you again for your input. Is it a ‘problem’ that needs remedy or just something that doesn’t look good. I know Freebear mentioned about taking it back to the brick and insulating, which we’ll probably do at some point anyway but if we didn’t do that, would it cause ongoing damage?

stuart45

It's not a structural problem, more of looks. Does it come back after painting?

Anoneemoose

stuart45 said:

It's not a structural problem, more of looks. Does it come back after painting?

I’m not entirely sure. This is the second colour it has been since we bought the house. The other was a lot more pale and I never noticed it until it has been this colour. At first I thought it might have become more apparent because of the general deterioration of the patio door but I don’t really think that’s the case. 

I’ve also just looked in the kitchen and I think I can see similar in there (same wall as they’re next to each other - just with the internal dividing wall), but the kitchen one is nowhere near as noticeable. And that has pale paint. Maybe that’s the answer. We are planning on redoing the dining room in a paler, more neutral colour so I’ll see what it’s like after that.