I just moved into an apartment two months ago and started noticing dark stains in the corners of the main bedroom. There hasn't been heavy rain, but the humidity's been really high lately. Is this normal in new apartments or should I complain to the builder? What can I do in the meantime?
Dark stains in the corners of a new apartment are usually mold, and they're right that daily ventilation helps. But there's an important detail: if the building is less than a couple of years old, the concrete is still releasing residual moisture from the construction process, so this is pretty common and temporary. That said, it's definitely worth filing a complaint with the builder because there should be a warranty covering construction defects, especially if the stains appear in multiple spots or are growing fast. In the meantime, besides ventilating, use a dehumidifier if you can (they're not expensive) and wipe the stains with a white vinegar solution every couple of days to slow down the mold.
Don't wait for it to go away on its own because dark stains in corners are almost always mold and they tend to get worse if you don't deal with them. Open the windows daily even if just for half an hour, keep the apartment ventilated and lower the humidity with a dehumidifier or air conditioning; at the same time, file a complaint with the builder because something's wrong if you're already having problems right after moving in, it's probably lack of ventilation or construction moisture that didn't dry properly.
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