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The bedroom at the back of my house (North facing) has what I would describe as persistent water "trails" on the inside surface. They are faint, but noticeable. The "trails" run from the ceiling, and are basically found on the entire wall.

I do not think the wall is insulated. To my knowledge, it is double-brick, finished with plaster and lath.

I am wondering what could be causing these and how to remedy?

I first thought they were surface stains, but they did not wipe away. I then thought they must be condensation, since the effect seems more pronounced in the winter. But it's only on the one wall (not on other walls of same room, or any other walls in house), so now I am not so sure.

I have seen these "trails" for a couple of years now, and recently noticed they seem more tacky. So I am now thinking the actual cause may be water seeping into the wall behind the paint.

The problem is, I cannot find any source of water into my home that might explain this. On a recent rainy day I checked both the outside of this same wall, and the attic space above - I did not see any obvious evidence of water problems anywhere.

The wall in question enter image description here

Detail of a section of water "trails" (just left of bookcase in 1st photo) enter image description here

outside view of the same wall (2nd floor) enter image description here

view of attic space directly above the wall in question enter image description here

  • Is that wall insulated ? From the photos I am not sure? If it is not insulated it could be from condensation when the room was painted changing the propertys of the paint. – Ed Beal Oct 13 '18 at 2:18
  • @EdBeal - no, I do not think the wall is insulated. To my knowledge, it is double-brick, finished with plaster and lath. I always thought it was some kind of condensation effect (and maybe it is), which is why I haven't asked about this in the ~2 years I've noticed it. If I understand correctly, you are thinking the lingering "tackiness" might be from the paint itself (due to changed properties)? I must admit I hadn't considered that possibility. – Roberto Oct 13 '18 at 2:37
  • What are we looking at in the last picture? In the 3rd picture, is the upper story window in the brick wall the outside face of the window in the first picture? In the second picture, those drip trails look wet. You can get lasting trails like that, but when they dry, they aren't usually that shiny and easy to photograph. If the paint is tacky, that sounds like an active situation. If the wall isn't insulated, and the inside humidity is high, you can get condensation like that in the winter in a cold area (and your profile indicates you're in Canada). Was the picture taken during the winter? – fixer1234 Oct 13 '18 at 5:18
  • @fixer1234 - sorry, I should have captioned the photos (I did now). The last picture is the attic space right above the wall. Yes, the third picture 2nd floor is the outside of the wall in question. Yes, the drips are slightly wet - that's what I meant by "tacky". The picture was taken a few days ago (about 15C / 59F outside; 21C / 70F inside), but the problem does seem worse in fall and winter. I originally thought it was condensation, but then why only the one wall? – Roberto Oct 13 '18 at 13:01
  • You could try taping a piece of clear plastic (sandwich bag, cut open to a single layer) onto the affected area to see if the moisture is coming through the wall, or onto the wall from the air in the room. Tape all the way around to seal the edge of the plastic... – DJohnM Oct 13 '18 at 23:00
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I wanted to comment on this but don't have enough reputation.

My childhood house had these marks in the basement on interior walls. They looked just like the marks in your picture. They only occurred on walls near my bathroom where people generally took long, hot showers.

I'm not saying this is the cause, but for me they clearly had a correlation with the steam from the shower. The more long and hot showers were taken the more visible the marks seemed to be.

Again, not really intending this as a good answer, but I cannot comment.

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That looks like the results of condensation due to an uninsulated exterior wall being much cooler than the inside temperature and humidity being high inside the room due to respiration overnight or nearby washbasins, bathroom etc, unventilated kitchen etc.

  • ... and the north wall would be the coldest, in Toronto... – DJohnM Oct 13 '18 at 22:56

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