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.
In new apartments, humidity is pretty common during the first few years because the construction releases a ton of water in the materials - concrete, plaster, all that stuff takes time to dry. Besides ventilating like the others are saying, try putting a small dehumidifier in the main room, especially in the corners where you see the stains; they're cheap and work great while the building finishes "curing." If in three months things don't improve even though you're ventilating and using a dehumidifier, then you should file a claim with the builder because there could be an insulation or filtration problem that's not normal. Anyway, your contract should specify what guarantees it covers during the first year - check it before you get into any claims.
I've seen quite a bit of mold in the corners, and what nobody mentions is that even if the apartment is new, that doesn't exempt you from claiming if the humidity is excessive or if there are construction defects (cracks, poor window seals, insufficient insulation). What is true is that materials release a lot of water at first, but two months with visible stains is a sign that something's not circulating air properly. In the meantime, cross-ventilate every day, use a dehumidifier if you can, and clean those stains with a solution of diluted vinegar or bleach so it doesn't get worse. The important thing is to document everything with photos because if you need to file a claim later, you'll have evidence.
While you're ventilating the apartment, the first thing is to check if there are cracks or leaks in the corners because mold only shows up where there's actual water - it's not just lack of air! If you find damage to the structure or broken seals, that's definitely the builder's fault and you have every right to file a claim during the warranty period. While you're waiting, wipe the stains with white vinegar and put a dehumidifier in that room, but without tackling the root cause you're not going to fix anything.
First, take photos of those stains with date and time because if you need to claim from the builder later, you're going to need proof of when they started. It doesn't matter if "it's normal" - if there's visible mold in a brand new apartment, that's a construction or design problem they need to fix, period.
What most people don't say is that interior corners are the worst because air doesn't circulate well there and humidity concentrates. While you wait to sort this out with the builder (and yes, you definitely should claim because this shouldn't happen in something brand new), you need to be aggressive with ventilation. Open the windows every day even if just to let air flow through, and if you can keep a dehumidifier in that room. Also clean the stains with a mix of water and white vinegar or with a basic fungicide - don't use pure bleach because it can damage the paint.
Now, the important thing: if the building is less than a couple of years old, the concrete and materials release a ton of moisture while they dry. That's real. But that doesn't mean the builder isn't responsible if there are cracks, poor waterproofing, or problems with window sealing. When you make your claim, mention that you're already ventilating regularly and it still happens - that shows it's not a lack of care on your part.
What the others didn't touch on is that air hardly circulates in corners, so even if you open windows, that area stays a moisture trap. Try putting a portable dehumidifier pointed directly at the affected corner for a few hours a day - it's way cheaper than waiting to see if it gets worse. In the meantime, yeah, definitely file a complaint with the builder because two months of visible stains is a sign that something in the construction or insulation isn't right, especially if other units in the building don't have the same problem.
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