Our winter guest: mould

While changing the sheets last week, Fran spotted green mould on the bed slats. Then black spots on the window sills. Then more on the curtains, and on the underside of the mattress.

Up here in Emerald, in the Dandenong Ranges east of Melbourne, winter means months of fog, rain and single-digit nights — lovely for the ferns outside, less so for the timber inside.

We'd met this mould before — the same slats, the same underside of the mattress cover, in December 2024. We cleaned it off and thought that was that. Cleaning treats the symptom, so this time we went looking for the cause.

That decision turned into a two-week investigation that took over the house. We started logging temperature and humidity in every room, several times a day, and we bought two dehumidifiers and a window vacuum along the way. What we turned up were things we didn't know about our own house — behind the tiles, under the floor, and in the ceiling.

The surprise wasn't where the water was coming from — showers, cooking, washing, breathing, the timber itself. It was that so little of it had any way out once winter closed the windows.

Over the coming posts we'll share what we found, what worked, what didn't, and what it all cost — the mould, the machines, the leak, the bed, and the washing.

Have you found mould creeping in this winter?

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24 comments

  1. You can also use the dehumidifier setting on your split system if it has it.
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    1. Michael Edgerton Thanks. I thought so too, but it turns out that only really helps on hot days, to take the "sweat" out of the air. But not effective in winter. Details to follow in a separate post.
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      1. Tesla Tripping
        Try heat the air first
        Free window spend 2hrs heating and one dehumidifying.

        Dehumidifying does cool the fan coils but runs the fan very slowly to give the water in the air a chance to condense without using shed loads of energy and substantially changing the room temp.

        In a multi storey house it's much easier. De-humidify up top and heat down below works great for us
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      2. Karl Jensen kinda like a giant hot burp. Get the heat to take it out of the building, fixtures, fabric etc. Then vent it out and reheat using free/cheap electricity. No mould anywhere. Since the bathroom got a thermo ventilator, even that is bone dry... Those nicer showerheads create a LOT of airborne moisture very quickly compared to the crap old ones.
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    2. Michael Edgerton DRY or COOL mode can dehumidify in summer. AC won't dehumidify much in winter.
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  2. We get it in summer (se qld). Not fun to keep controlled.
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    1. Andrea Dacey Oh true. I had forgotten about the flip side closer to the tropics – probably worse than here. I have heard/seen that many have to keep fans running 24/7 to avoid mould.

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      1. Tesla Tripping definitely need air conditioning when wet outside. But solar covers it and our Tesla❤️
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      2. Andrea Dacey Yes, summer especially brings an abundance of free solar energy.
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  3. Not since we bought a dehumidifier, amazing how many times we had to empty the drawer but eventually it takes longer and longer to fill it, then onto the next room. Even open closets and clothes cupboards. No more mouldy leather jackets. In fact keep an eye on them coz they need some moisture left in the leather. Then it's just an occasional yearly quick going over
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    1. Sandor Kovacs Yes! We have bought two dehumidifiers since this happened and are amazed. Stay tuned for upcoming posts about them.
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  4. I'm very fortunate all our showers have windows opening. We close the shower doors and leave the windows open all day long.
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    1. Vincent Lui Great advice.
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  5. We haven’t had mould at our place but it is very common in the hills. When it is not too cold we open all the windows in the morning & leave them open most of the day but we have definitely done that less this winter. We are now all electric so have been running the heater during the day when we are inside so that probably keeps it drier. We have traded Zap in on an XPeng so you will have a white car to wave at in a month or so. Red smell (Equinox) will be up for sale soon so another step further on our electrical journey.
    I will be interested to see how you fare with the mould. Hope the dehumidifiers are effective
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    1. Anne Meyers Yes (spoiler alert), we’ve had success purging a room after we’ve heated it.

      The heating sucks moisture into the air. Previously, when we would turn off the heat, all that moisture would deposit on cold surfaces, like windows and bed slats, eventually causing mould. See upcoming posts.
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    2. Anne Meyers Oh wow, an XPeng replacing your MG4. Why the change? We really liked the XPeng G6. It was a contender against the Tesla Model Y when we were looking.

      XPeng G6 — second test drive

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    3. Anne Meyers You decided you didn’t need your “red smell” petrol vehicle after all?

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      1. Tesla Tripping We won't need it once we have the long range fsst charging xpeng. The mg has been a bit limiting for us on long trips
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      2. Anne Meyers Interesting. Limiting in terms of charging speed, or other things as well?

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      3. Tesla Tripping Charging speed was slow & the range reduced by around 30% when we carried our electric bikes on the back so it was difficult to do long trips. Also the space inside was not enough for all our stuff. We drove the xpeng around 6 mths ago& liked the comfort & the technology but the price was a bit high. When they rang us the other day with a very good offer on the 2025 model we decided to do it. Apparently they have fixed the problem with using the Tesla fast chargers but that remains to be seen. Xpeng are supposedly installing their own super fast chargers around Australia later this year so that will make a difference. We have not seen many xpengs on the road & everyone we mention it to says what car? So maybe the company will vanish or maybe thrive - who knows?
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      4. Anne Meyers Yes, I do believe that the Tesla/XPeng issue was fixed a few months ago. The tech and comfort of the Xpeng seemed top notch. We only just picked the Tesla over it.

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  7. How did you clean the mould please?

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    1. Cliff Laurens Coming up in detail in another post. We cleaned the slats with vinegar, then sanded, then coated them.

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