I'm trying to learn possible causes for flat, pale floor-to-ceiling, slightly powdery spots in unventilated UPSTAIRS storage closet that shares one interior wall & crawlspace w/a bathroom that had major leaks in 2020.‡

Note: Closet & Bath are entirely separate rooms - doors open ~3 ft apart onto Landing. I'm thinking spots stem from 2020 UPSTAIRS leaks flowing through crawlspace because the previously cleaned DOWNSTAIRS bathroom registers have since rusted.† Cannot find evidence of leaks anywhere in house/attic.

If possible, how would a contractor fix? Would DOWNSTAIRS bath ceilings & closet's walls need replacing? How big a job is this? etc...

Spots are on all closet walls floor to ceiling. No spots on popcorn ceiling or semigloss door/trim. Walls have Flat paint. Dark areas in below photos are scuffs.

Closet w-minor crop

Closet wall closeup

My teen just told me Exhaust Fan hasn't worked in 6mo - been leaving door open after showering. No mold/mildew/spots seen in bathroom, no rust on UPSTAIRS bath's HVAC registers. Fan's being fixed.


  • RIGHT: bath sink/shower
  • LEFT: FROG w/HVAC rarely used. Unheated garage below.
  • BELOW: crawlspace between floors
  • REAR: exterior sunny wall
  • ABOVE: attic; difficult to access due to roof angles
  • DOOR: opens to Landing, ~3 ft from bath's door


  • 8/2020: Failed shower valve; gallons gushed into DOWNSTAIRS bath primarily around HVAC vents. Left ceiling w/widely separated wet areas in ~12x8 bath.
  • 10/2020: Tub shoe gasket failure caused less severe DOWNSTAIRS leaks around HVAC registers.
  • Both times followed plumber's instructions: remove HVAC registers, run very cold HVAC + individual fans on ceiling areas 24/7 for 2+ weeks.

† DOWNSTAIRS HVAC registers were removed & cleaned late 2020. They've since rusted as seen on 2022 photo below. 12-2022 DOWNSTAIRS Register, no rust 10-2020

My teen just told me Exhaust Fan hasn't worked in 6mo - been leaving door open after showers. No mold/mildew/spots seen in bathroom or rust on UPSTAIRS bath's HVAC registers.

Am NOT fixing myself - on fixed income & need knowledge to know if I should involve insurance & to avoid being taken advantage of again. I greatly appreciate any & all advice. Thanks!

  • 1
    that is caused by high humidity
    – Traveler
    Dec 25, 2022 at 23:43
  • Thanks for your help. My description wasn't clear. Closet w/spots is an entirely separate room that's next door to bathroom. Each room opens to large landing & they only share one interior wall. I left DampRid in closet for 10 days & no moisture was captured. Bath fan's being replaced. Son's left door open after shower - no mold/mildew found in bath (yet).
    – Pepe's Mom
    Dec 26, 2022 at 15:45

1 Answer 1


Bathroom fan has one main function.

To remove the humidity.

If it is not working the humidity will be on the walls and after time mold will grow.

It starts as round spots.

Your AC ducts are either aluminum or galvanized steel, with do not rust.

However the air vent register is only painted steel and will rust.

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