The first sign in my old ground floor flat was not mould. It was a smell that arrived in late October, somewhere between wet cardboard and old coins, strongest in the corner where the wardrobe met the north wall. I pulled the wardrobe out in November and found a grey bloom spreading along the skirting, roughly the size of a dinner plate, with the plaster underneath still faintly cool against my hand.
Ground floor rooms fail in ways upper floors do not. The slab sits against soil that holds its summer temperature late into the year, so the lower metre of wall runs several degrees colder than the air in the room. Once the heating goes on and the windows stay shut, moisture from cooking, drying laundry and simply breathing has nowhere to travel, and it settles on the coldest surface available. That surface is nearly always the wall behind furniture, where air never moves and nobody looks until the smell starts.
Sorting condensation from rising damp matters before any money is spent. Rising damp leaves a tide mark that stops at a fairly even height and often carries salt deposits that crunch under a fingernail. Condensation mould appears in scattered patches at cold bridges and behind objects, and it recedes in warm months.
Mine was condensation. No tide mark ever appeared, and the patch shrank on its own by April.
So the question became which machine. I spent a winter reading appliance comparisons, including a roundup on beyondspectra written for the Korean market. A long summer rainy season and housing stock dominated by concrete apartment blocks have pushed dehumidifier retail there into a wide range of compressor and desiccant models, so both types sit at similar price points instead of desiccant being a specialist import.
- Leave a 5cm gap between furniture and any external wall so air can circulate.
- Run the extractor during cooking and for ten minutes after, not just while the pan is on.
- Dry laundry outdoors or in one room with the door shut and a window cracked.
- Check the gutter and the ground level outside the affected wall after heavy rain.
- Keep the room above roughly 16C rather than heating in short bursts.
Season changes the machine. Compressor units lose efficiency once the room drops toward 15C, which is exactly when an unheated hallway or a back bedroom needs help. Desiccant models keep working in the cold and give off a little warmth, at the cost of higher running power.
None of this replaces a structural fix. If the damp course is bridged or a downpipe is discharging against the wall, drying the air only slows the damage. Photograph the patch each month, note the dates, and give the landlord a record rather than a complaint.