A.Frank Vigil, senior building science specialist at Advanced Energy in Raleigh, N.C., responds: Dusting, sooting, or ghosting — as these marks have all been referred to — is not uncommon. Markings on walls, carpeting, furnishings, even inside of appliances, are all too common in today’s houses, possibly because we’ve done exactly what we set out to do years ago: build the houses tighter. In tight homes — especially tight homes with insufficient ventilation — particulate has more opportunity to deposit, instead of being flushed away by regular air changes.

The dusting or staining that your homeowner is experiencing requires two things in order to occur: There must be a source for the material, and there must be a driving force to cause the material to deposit. A laboratory test of the material can be helpful, at least to narrow the possible sources. Is the staining gray, black, brown, or yellow?...

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