There is a mystery afoot. From move in day about 2.5 years ago, the studs in the exterior walls and ceilings of the master bedroom have been clearly visible through the drywall (attachment 1 & 2). In the ceiling, black blobs are visible as well (attachment 1 & 2). We thought that it may have been a stain from candles that were burning below, but the blobs haven’t changed over time. Also, there are similar blobs in other rooms of the house. We painted several rooms shortly after moving in, and the black blobs are already coming back on the ceilings. These didn’t show up very well in the pictures so far, but I can try again if needed.
Another clue may be that the nailheads into the ceiling studs are slightly darker(attachment 3).
The attic is very dry with no sign of water leaks in the roof’s plywood. Most of the house has a brick exterior and the black areas can be rubbed off by hand. These points don’t lead us to think that the problem is mold. The attic side of the ceiling doesn’t show any discoloration.
After discussing this with a respected home builder, our current assessment is that there is air moving through the drywall with the studs stopping any dirt in the air. The dirt collects over time and is making those areas look darker than the rest.
Any advice on what the problem is and how to fix it would be greatly appreciated!
Replies
That is most likely soot from candles; possibly from your furnace (big, dangerous problem if so.)
There are 2 theories as to why they happen.
The one I like is the "increased deposition hypothesis." That holds that there is increased air movement where the insulative value behind the drywall changes (insulation v wood) and there is increased air currents and eddies at that point, leading to more air and dirt particles hitting at those areas.
I like that hypothesis, but the one I believe is the "condensation hypothesis" which holds that cooler areas of drywall are more likely to have condensation at times and thus have soot stick.
I believe the second because of the "blobs" as you describe them.
Betcha there is missing insulation at each of those blob spots.
Candle soot is difficult to clean and is prone to bleed through.
Now that you've painted, your only hope is a stain blocking primer.
PS, to check to see if it's mold, dab some bleach on a spot: mold will bleach out; soot won't.
I think Bob is right. Do you burn candles or smoke indoors often? Cooking often with out a vented hood may add to this syndrome.