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I've got spots on my ceiling in one of the bathrooms in my house. There are 3 spots in a straight line. They are perfectly round and very small. I am thinking they are the nail heads as magnets stick to them. The spots are cold and seem lightly damp. I am thinking it is condensation on the nail heads as they must act as a conduit for the cold to come in from the attic.

How can that be fixed? I cleaned my bathroom fan and I think it's about 15cfm under the HVI recommendations. It was very dirty, so I don't know if maybe it's not drawing out enough humidity from the air?

What should I do?

John Arg
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  • What do you mean by "fixed"? Do you just not want to see them anymore? – CactusCake Jan 15 '18 at 22:08
  • Yes, I don't want to see them anymore. – John Arg Jan 15 '18 at 22:09
  • Is there some reason why painting over them would not be sufficient? – CactusCake Jan 15 '18 at 22:10
  • The paint takes long to dry, and then they come back. – John Arg Jan 15 '18 at 22:10
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    If they are indeed nails, then the returning discoloration after painting may be from corroded metal leeching into the paint while it's still drying. You'll need to either replace the nails with something that's a bit less reactive with water (like brass or stainless steel), but they could be tricky to remove if they've been sunk flush with the ceiling. Instead, you could use a punch to drive them a little bit deeper, then fill the resulting crater with plaster or vinyl spackling, then paint. That would distance the paint layer from the metal a bit, hopefully enough to prevent staining. – CactusCake Jan 15 '18 at 22:18
  • OK, Thanks. You don't think it can be condensation forming on the nailhead because it conducts the cold down from the attic? It seems slightly damp to me but it's hard to tell because of how cold those spots are. – John Arg Jan 15 '18 at 22:34
  • You're probably right about the cold and condensation. But if the nail head is buried deep enough that should cease to be a problem. – CactusCake Jan 15 '18 at 23:17
  • OK, can it be an insulation problem in the attic? Should I go look? – John Arg Jan 15 '18 at 23:54
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    Drywall screw locations are often also the first place a roof or plumbing leak shows itself. Water runs until it finds a way thru. – Tyson Jan 16 '18 at 00:05
  • please edit you're post to include a photo – Jon Jan 16 '18 at 14:47
  • Use one of these https://amazon.com/Etekcity-Lasergrip-774-Non-contact-Thermometer/dp/B00837ZGRY/ if you want to determine if the area around the nail heads is colder than the surounding area. – Jon Jan 16 '18 at 14:48
  • It's definitely colder. – John Arg Jan 16 '18 at 17:25

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The nails penetrate the ceiling and some insulation so they get cold enough for condensation to form. This leads to both rust and mildew by the heads.

Before you clean up the rust and/or mildew, replace any insulation above the bathroom that may have been damaged and add additional insulation above the joists to prevent a recurrence.

DrMoishe Pippik
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