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Yellow Spotting on Painted Interior Wall

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I have recently moved into a 5 year old townhouse in CA. A bath above a bedroom apparently leaked at some point and water came through a ceiling corner in this bedroom. There was about 1 sq ft of mold growth on the ceiling corner surface which I have recently cleaned up and will be inspecting behind the drywall this weekend.

I am posting about some dark spots that I recently noticed on the walls in the same bedroom, but away from this ceiling-corner. The spots are vertically aligned, but on only 2 walls, so I assumed they were from some type of poster-hanging-putty the previous owners may have used. However I see some yellow around the dark spots which has me concerned a bit. Any idea from the pics? Putting up to a blacklight, the yellow color really stands out. I checked in the attic and don't see any signs of water damage to the walls with these 'spots'. Also I never even noticed these spots until a few days after I cleaned up the mold in the ceiling corner; could mold spread and grow if there is no moisture issue?

I've been reading through these forums and it's been a great resource.

Thanks for your help.

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Hello Safoo!

Close-up photos are never as good as people like to think they are.

In any event, the discolorations are due to condensation. They line up along cold spots – in this case the ceiling joists, and the nails in the drywall.

As water condenses it does two things: 1) Draws contaminants out of the air with it, and 2) draws solubles from the substrate. Then as it dries, the water soluble materials precipitate out leaving distinctive discolorations.


Caoimhín P. Connell

Forensic Industrial Hygienist


(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)


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Good to hear. If I didn't know of the mold problem in the home, I would not have thought twice about these marks on the wall.

I will say I just came across this forum, but I think I agree more with the views towards mold on this site more than any other.

Thanks for the info and I will continue to check in as I try to complete remediation of my current mold problem.

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