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Question DetailsAsked on 2/2/2017

are the black streaks on my wall dangerous? I have them in all roams and some are very black....thank you

I rent and I have black streaks in all rooms and they outline all the rafters in the house and some go down the walls. I am concern for the danger with mold. We are always sick.

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2 Answers


If these follow studs and roof trusses or joists, they are called shadowing or stud ghosting or thermal tracking or other similar names, and are due to condensation on the wall when it is cold outside - cold enough that the studs or attic floor joists/trusses exposed to cold air cause the plaster/drywall at that point to get cold enough that is drops below the dew point - causing condensation on the surface. This moisture then catches dust and makes the shadowing - which if not washed off frequently permanently stains the wall. In severe cases where the humidity in the house is quite high (typically over about 50-60% though can be much lower if very cold outside), mold can form there also. This is basically the same mechanism that occurs with windows - get the inside surface below the dew point and you get condensation on it, so I am sure you have windows running condensation (which can damage the frames and underlying wall) or maybe even icing on the inside of the windows.

If this is just diffuse gray to light black shadowing, then it is likely just dust and not a health concern. If you look closely and can see roundish concentrations (other than at drywall fasteners, which can also do this shadowing around the fastener head so it round but may not be moldy) with growth tentacles or wavy or feathery fringes, then is almost certainly mold. Also, if quite black and spotty - rather than grayish and sort of blending in at the edges to the wall paint, is likely black mold - NOT a good thing to be breathing in.

Google for search phrases like - images of mold - and - images of stud ghosting - for pictures of what the two look like. Generally, if you wash it off well, ghosting will disappear or stay as a faint fairly uniform discoloration or stain, mold will show the roundish circles of discoloration and the growth tendrils of the mold as it spread and be variable and splotchy - definitely not a relatively uniform appearance.

Mold Testing and Remediation would be the Search the List category of company to remove it if you cannot DIY and if it is mold. Bear in mind any testing they do WILL test positive because pretty much every surface in a house which is not cleaned daily will have detectable mold on it - the key is the growth pattern of active mold, as opposed to just the stray spores which are in the air by the millions in every house but a mold test will commonly test positive for. A black light also does an excellent job of showing the growth patterns of the active/live mold.

Of course, remediation will be an on-going thing unless the source of the excess humidity and ghosting is solved - through better wall/siding/attic insulation (a major effort in an older hosue), more air changes in some cases, running the indoor temperature higher to keep the surfaces from dropping below the dew point (especially if only condensing on a few colder days), using dehumidifier, etc - lots of ways to address it, which a Heating and A/C contractor can help you with. Since it sounds like most attic floor joists are ghosting through the ceiling drywall but only extending partway down some walls, sounds like possibly attic moisture and poor insulation might be an issue. And possibly settled insulation in the walls (has creeped down by gravity so there are uninsulated sections at the top), which can be solved with blowning-in insulation at the top of the walls through holes in the drywall.

The first steps in reducing the moisture promoting this is reducing uncontrolled water sources - using bathroom fan during and for at least 1/2 and preferably 1 hour after showers and baths, covering cooking pans/pots which are boiling and using a kitchen exhaust hood fan to remove cooking vapor, making sure clothes dryer is properly venting outdoors, covering fish tanks (with proper makeup aeration system as necessary to oxygenate the water), reducing indoor plants - especially ones with significant exposed soil area or types which evapotranspire a lot of moisture, and removing moisture from the area around and over hot tub / sauna / jacuzzi / indoor pool etc so it does not spread throughout the house.

Eliminating or using vapor barrier to block out basement/crawlspace moisture, especially if connected to house airspace, can also be a major factor in some houses.

I would suspect if you are always sick, while mold/mildew might be the cause the ghosting itself is likely only a symptom or a larger problem, with more mold in greater concentration elsewhere in the house maybe being the primary cause - in the basement, bathroom, in forced air heating system ducts, etc, because I don't think I have ever seen visible mold on stud ghosting without there being other much more pronounced mold elsewhere in the house.

You said you are renting - so unless you have a zero-net type lease where you are fully responsible for all maintenance and repairs, this might be a joint responsibility between you and the landlord - you to control or remove sources of excess moisture you create, maybe the landlord for proper ventilation and heat and dehumidification and removal of natural water sources like wet crawlspace or basement.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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