Black "ghosting" on the walls

[Clayton Swansen]

Hello everyone! Well, I recently made the plunge into the world of REI with big thanks to Bigger Pockets, and my local investors group. I am extremely excited, and nervous about my new life as a landlord. I have already dealt with a few small challenges, but this one I felt the need to bring to the BP forum...

One of the units in my triplex has this black stuff all over the walls. It looks like soot. I thought it was from burning candles, but the tenant does not burn many. She has been in the unit for 22 years, and has no idea where it could be coming from. She had it tested, and it is not black mold. It seems worst directly above the baseboard heaters, so my thought is that the heaters are burning dust when they are on. Does anyone have any experience here? Any good advice?

Your help is greatly appreciated. Thanks, BP!

[Sam LLoyd]

One thing I've found, is that if your paint is very thin, or old (22 years would qualify), the air can actually move through the sheetrock, however, any dust in the air does not go through the sheetrock... it acts as a filter.  I had one place where there is a lot of wind creating a negative pressure outside... You could see every seem and every sheetrock screw under the paint because they were black from the 'filtration soiling'.

If there are patterns that reflect any seems or fasteners, this would be my guess... in which case a good coat of paint would help seal it.  If it's completely uniform, this might still be the culprit, but I doubt it.  Has this been related to the weather or seasons?