White powdery stains on hallway ceiling under air handler unit. Has anyone ever seen this type of drywall issues?
What does it look like from the attic?
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Morning, Robert.
Can you be a bit more descriptive? Drywall, Grout or Plaster and Lathe finish?
Is this hard crystalline substance or powdery and can be rubbed off or a bit of both?
My first thought is Efflorescence.
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Probably hunteresque… 
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The air handler is over top of the spot.
Knowing this, what do you suspect the issue to be?
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It is Efflorescence.
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Drywall was the material for ceiling
I could not find anywhere that efflorescence was a produce through drywall.
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What is efflorescence and how is it produced?
Moisture intrusion into the a surface of natural or man made material, where it forms a powdery coating.
I just have never seen it in drywall, without the drywall in contact with block wall material. That’s why I reach out to the board to see if anyone has encountered efflorescence through drywall not touching a block or concrete type of material.
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Powder, can be rubbed off. My first thoughts was efflorescence, I just never seen it pass through drywall like this
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Again…
The answer is very basic and primary with moisture intrusion.
Are you sure it is drywall? I can see plaster forming efflorescence.
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Me either. Cool find. In my experience, drywall with moisture issues presents itself far differently.
I’m with Scott. Plaster material would be easier accept, but I have not seen that either.
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Yes its drywall
if You tried snorting it and all You got was a salty taste in the back of your throat it was efflorescence…
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When was thehome erected
Thats what im having a hard time about, I’ve seen it in plaster, but not like this in drywall.
1965 Robert