Moisture maybe.
Any leakage or cold air draft in the corners and in the middle?
Any leakage or cold air draft in the corners and in the middle?
Strange with round patterns that are so clear. When did the spots appear? Depending on where you live in the country (temperature) and if it occurs in connection with, for example, showering, cooking, or if there are suddenly a lot of people indoors, I would guess it's condensation water from the inside of the window/frame. But at the same time, it should be noticeable from the beginning in the house. Do they disappear when airing out? The alternative is that some house elf is there, dripping oil on the board. No one has been greasing something on the window that then drips down?
Moisture from outside, well indeed, but it's so clear with the round rings. Some old glue they used to attach the board with that's starting to reveal itself maybe? Feel, smell it, does it disappear with a hairdryer?
Do you have pets and have had the window slightly open for airing in the summer?
After much puzzling over why it suddenly was drafty around the window at home, I saw with my own eyes: The cat thought it was fun to tear and chew on the rubber seal and then run off with the loose piece
Draft over stone slab + humid indoor air that condenses. But the spots feel "neatly" placed; the ones in the corners are almost exactly the same size.
If you don't notice any difference after blowing with a hairdryer for a while (not too close and too hot), then a boring glue/sealant might "smear" a bit. If the spots had been further out on the board, I would have thought it was due to pots.
I'm out of examples now.
Moisture from outside, well indeed, but it's so clear with the round rings. Some old glue they used to attach the board with that's starting to reveal itself maybe? Feel, smell it, does it disappear with a hairdryer?
Do you have pets and have had the window slightly open for airing in the summer?
After much puzzling over why it suddenly was drafty around the window at home, I saw with my own eyes: The cat thought it was fun to tear and chew on the rubber seal and then run off with the loose piece
Draft over stone slab + humid indoor air that condenses. But the spots feel "neatly" placed; the ones in the corners are almost exactly the same size.If you don't notice any difference after blowing with a hairdryer for a while (not too close and too hot), then a boring glue/sealant might "smear" a bit. If the spots had been further out on the board, I would have thought it was due to pots.
I'm out of examples now.
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