I visited my mothers house and saw this pretty uniform spread of substance on the ceiling. Before I go start ripping it out I wanted to see if anyone has experienced something similar?

This is an office underneath a 2nd floor bathroom, so my thought is there's water somewhere, but it's so uniform it's making me question that...


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  • 1
    Usually a water leak from above will be centred under the leak and spread out. This looks more like high humidly/moisture from below going up to the ceiling. Or someone smacking flies on the ceiling.
    – crip659
    Sep 7, 2023 at 18:20
  • Thanks crip659, that's where my hesitation comes in for ripping out drywall. It doesn't seem to have a definitive spot where moisture is collecting. Would mold like this spread from a wet insulation or something that would spread it? Like could the upstairs bathroom have a pinhole leak that doesn't wet the specific area of the lower floor ceiling but adds enough moisture for this type of growth to occur? Sep 7, 2023 at 18:29
  • How big of an area is it? Even a pinhole leak in the supply pipes will be 24/7, that will only take a few days to make itself known. Ceiling falling down. Drains should not have enough pressure to move the water away from a point source.
    – crip659
    Sep 7, 2023 at 18:48
  • it's pretty uniform along the sliding door exit from the office to the outside. Probably a 15ft length of wall and around 4ft or so into the room. Sep 7, 2023 at 18:55
  • Sound like it could just be moisture trapped in the room from winter? I may just try and clean it off and see where that gets us. Appreciate the advice Sep 7, 2023 at 18:56

2 Answers 2


No! Don't rip out the drywall. These look like the typical mold that grows in areas of high humidity. Just wipe it with a rag that has some diluted bleach. When painting over it, use a mildew-resistant paint.

If they reappear, try a dehumidifier.

  • Appreciate this! Sep 7, 2023 at 21:35

I agree with wiping it down with some diluted bleach.

Usually when there is some type of bathroom leak in an upstairs bathroom, you will see brown spots on the ceiling downstairs.

Because there is no apparent brown stains similar to that, it tells me that you’re most likely dealing with high humidity.

To be sure, you can use a small humidity meter, or a moisture meter.

Or if you think it definitely feels humid in there and grab a dehumidifier, try to keep the humidity set around 40.

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