I had a bathroom mold problem and told my apartment supervisor about it. They came and cleaned it out and now they want to leave a fan on it over the weekend to dry it out after they coated it with chlorine bleach. That seems like too much time to dry to me. Or are they doing it right?
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Operating a fan will lower the indoor humidity (which will keep the mold from coming back), but only if the outdoor air is either cool, or dry, or both. If you live in a climate with hot, humid summer weather, it's hard to lower indoor humidity levels with ventilation. But if the air outdoors is very dry, as it often is west of the Rocky Mountains, then ventilation is a good strategy.
If your bathroom has a mold problem, it can only be solved if you understand and correct the problem that created the high humidity conditions that allowed the mold to grow in the first place. Otherwise the mold will just come back.
The most important weapon against bathroom mold is an exhaust fan; this will only work if it is used regularly.
In a cold climate, mold on a bathroom ceiling is often a sign of insufficient ceiling insulation, especially near the perimeter of the attic. (Cold drywall allows moisture accumulation during the winter.) If you aren't sure why your bathroom developed mold, you may need to talk to a home performance contractor who is familiar with this type of problem.