Filled cracks in plaster reappearing in warm temperature

[Sabina77]

My son’s room has just been redecorated and previously he had a lot of fine cracks in the plaster on the external facing wall. They’d appeared gradually over about 5 years and were vertical and horizontal. The decorator filled them and repainted two weeks ago. Then one warm evening after he’d finished, some of the cracks reappeared. The next morning I could barely see them again, and decided it was because the room was cooler. Now again this evening, after it being a warm day, those same cracks are really visible again.

I’m presuming the original cracks are expanding and contracting with the change in temperature, meaning the filler didn’t actually do the trick at all. Can anyone advise what might be the root cause and whether it’s actually possibly to fill cracks permanently that are appearing and disappearing in this way? Thank you

 

[securespark]

Have you got any pictures?

 

[Pharun]

As already stated, some pictures would help,
Are the cracks above a window?
is it an old house?
any additional information will help us help you

 

[Sabina77]

I’m attaching photos but I’m not sure what the resolution will be like once they’re uploaded and you look at them. The cracks are less than a millimetre wide. I’ve marked up a photo of the entire wall to show where they are. The ones on the left appeared within a week of being filled, as soon as the room was warm, and the horizontal one on the right has just reappeared today in the warm weather.

The wall is an external wall in a 1960’s semi. There’s no window on this wall.

I believe there may have been a chimney breast on this wall decades ago because there is one in the room directly below. It would have began just to the right of the chest of drawers in the pic though, not sure if that’s relevant.

Any ideas why the cracks have reappeared? Do cracks normally expand and contract with the weather? What kind of filler should have been used?

 

[Pharun]

This is a bit of a toughie without actually being there, I doubt there is a structural issue but I suspect that it may be an issue with the backing wall , it's hard to say , I have some cracks in my home that appear occasionally, and it is down to the electric conduit not adhering with the plaster coating, I dealt with it by prior to decorating I cut a "V" cut into the crack and filled it partly with a bit of flexible filler and then cut the finish plaster back enough to accept a length of fibre tape scrim and pva'd it and patched it with a bit of finishing plaster , as I say the cause is difficult to assess without being there and if the outside external wall has no issues ,this could be down to different backings that are reacting to different circumstances/temperatures, that said a lot of old houses do tend to move a lot, sorry I couldn't offer any better resolution,
EDIT
the only other thing I can think of is if it was part of a chimney then there would have been soot deposits and sooted walls have to be treated prior to plastering otherwise they produce mineral salts and fail/blow, but I don't think that is the cause but it is worth bearing in mind
I leave this open to others to offer their take on it.
PS.
Does the wall sound hollow or solid when you tap it?

 

[ree]

OP,
Its probably minor thermal movement, nothing to worry about.
Is the wall covering solid plaster or plasterboard?
Can you show a pic of the outside of the wall?
Is it a cavity wall?
Any soot remaining on a chimney flue back wall theory is irrelevant.

 

[Pharun]

edited

 

[Harry Bloomfield]

Those first two photos, suggest to me that there is plasterboard under the plaster - neat, almost square corner of the crack.

 

[Pharun]

That had crossed my mind that's why I stated it could be a different backing problem , they may have dabbed a board over the sooted chimney area to make it easier to plaster but without being there this is a tough one, good call

 

[Sabina77]

OP,
Its probably minor thermal movement, nothing to worry about.
Is the wall covering solid plaster or plasterboard?
Can you show a pic of the outside of the wall?
Is it a cavity wall?
Any soot remaining on a chimney flue back wall theory is irrelevant.

It’s solid plaster I believe on a brick wall. I’ve attached a pic of the outside wall. I’m not sure how to tell if it’s a cavity wall or not.

If it’s minor thermal movement, I’m wondering what would cause that to start after there having been no cracks at all for a number of years. Also, can they be covered/filled permanently somehow or do we just need to live with them? Thanks.

 

[Sabina77]

That had crossed my mind that's why I stated it could be a different backing problem , they may have dabbed a board over the sooted chimney area to make it easier to plaster but without being there this is a tough one, good call

The wall generally sounds very solid when knocking on it. There are areas that sound a little less solid around where the cracks are though. I appreciate this is hard to know without looking in person! Just want to know why they’ve returned and what I can do to make them gone, really. It’s a bit disconcerting to see so many cracks on a large expanse of wall.

 

[Harry Bloomfield]

It’s solid plaster I believe on a brick wall. I’ve attached a pic of the outside wall. I’m not sure how to tell if it’s a cavity wall or not.

That appears to be a cavity wall. The way you can tell, is by the brick pattern. A none cavity wall, would show the short faces of the bricks, in a regular pattern. Your wall just shows the long faces, over that entire wall.

 

[Sabina77]

Oh I see. So does it being a cavity wall suggest what might be going on, then?

 

[Harry Bloomfield]

Oh I see. So does it being a cavity wall suggest what might be going on, then?

Best guess, there was some poor quality plastering work, when that chimney breast was removed.

 

[stuart45]

I've had the best results for minor plaster cracking using the tape and fill method.
I normally bed on paper tape and 3 more coats using Knauf fill and finish. It sands down to nothing, so when painted shows no edges.