Shadow Lines At Studs

[Jim]

Over the years I have noticed in many houses gray lines on the sheetrock where the studs are. I first thought it had to do with heat transfer from the outside but I have aslo seen it on inside partitions. These lines do not wash off and have to be re-painted to get rid of them. Does anyone know what causes this?

[Bob R]

This sometimes happens from burning candles.

[GaryR]

Jim,

Do a search. I believe this subject had come up before and it was interesting to here peoples thoughts on it. The candle thing sounds familiar though.