Mould - Losing My Mind a Little

Dear internet hive mind,

I humbly request your opinions / knowledge / counsel.

TL:DR; We moved into a new unit and (accidentally) brought mould with us. It spread madly. We've cleaned away 95% of it or so. We bought a humidity monitor and it seems we are always between 59% to 67% humidity, despite having two windows permanently open, doors open, wardrobes open, running exhaust fans and the rangehood etc. Is it just going to keep growing back?!

Full story:

We (accidentally) brought some mouldy items with us when we moved into a brand new ground floor 2 bed 2 bath unit in early Feb this year. The mould spread fast in the smallest bedroom (which we were using as temporary storage) before we noticed it. When we'd finally noticed it, it had spread to the main bedroom wardrobe, and started to appear throughout the house as well: mainly on fabrics and clothing, eg handbags, backpacks, dark clothing, shoes.

Up until then, we had always used the exhaust fans in the bathrooms, but admittedly we didn't open the windows at all for a few weeks (waiting on a flyscreen).

When we noticed the mould, this is what we did:
* Threw out the worst of the mouldy stuff
* Immediately bought damprid and put some in the worst bedroom, and some in the wardrobe of the main room
* Started keeping 2 windows open 24/7 for ventilation
* Kept using exhaust fans as normal in the bathrooms, but now [/also/] left them on for longer (even after we'd finished the shower)
* Cleaned about 95% of the leftover mould - this has been a long process because I had to take out ALL our clothing in the main wardrobe, and towels/linen, and shoes… and wash it all.. and dryclean some.. etc.
* We don't run any heating, we don't have any indoor plants, we never dry clothes inside, no fish tanks, we cook with lids on and a rangehood.

Before putting everything back into the wardrobe, I wanted to check if our home still had conditions that were conducive to the growth of mould - despite the list above. So I bought a humidity meter - I know it's probably inaccurate as it was a cheapie… but it reckons we are at 60 - 67% humidity all the time, which seems far too high.

Is the mould going to come back? Why is our humidity so high? What can we do about it? Even with all our windows open, and a sliding door open, and a rangehood whenever we cook (not much), and exhaust fans that run longer than needed, and every internal door open… we can't seem to budge that number.

By doing some reading, the internet said there could be a leak somewhere in the walls or floor… but according to the humidity meter we have, it's about the same all around the house.

We tried the "dry" mode on our ducted air con, and it works! Got it down to about 56%. But it makes the room verryyy cold despite checking the temp settings.

H E L P. Is your home's humidity also high? Can we do anything, aside from just buy a dehumidifier for the whole house and a crapton of damprid? Is this common in new builds? I am sick of cleaning, and paranoid it'll be back.

Thank you so much in advance for any thoughts you have.
PS: We are in Sydney.

Poll Options

  • 2
  • 1
    Yes, that humidity sounds too high to be normal.
  • 3
    That humidity sounds normal.
  • 45
    I think something weird is happening - get a mould inspection.
  • 4
    Sorry, I have no idea but I also hate mould.


  • +1

    Answered your own question. You need heating.

    Any humidity in the air will condensate on cold surfaces.

    • Sorry, not sure what you mean? We don't have any condensation anywhere at the moment. Are you saying we need to be heating the house? It's an OK temperature though…

      • +1

        I'm not sure if it's condensation or not without more info. But no matter the level of ventilation you need heat to make the ventilation effective.

        If the moulds occurring in areas with poor air circulation such as cupboards with no heat it won't change.

        Opening a window is effective to remove the internal humid moist air. If its cold on the inside the humid air likely won't escape

        Its probably getting worse this time of year due to the colder weather

  • +1

    That humidity range is within normal, but preferably <55% to prevent mould growth.

    AC doesn't have to be on drying mode to lower the humidity. You can put it on any temp that's comfortable. If you're feeling cold atm, you can use dry mode with a higher more comfortable temp, or put it on heat mode to dry the air out.

    I would ask other unit dwellers if they're having similar problems. If you're concerned, I'd call in some professionals.

    • Thanks for your thoughts! Yes I'd read <55% is best, but ours is mostly 59-67% thus my worry.

      We tried to use drying mode at a higher temp, but it only seems to actively dry the room when our room's temperature is lower than the temperature that's been set. eg. our room is 18C at the moment, and if we set the AC 'dry' on 22C, it doesn't seem to do anything. But if we set it at 17C, then it works, the humidity drops, but so does the temperature.. :/

      You mentioned putting it on heat mode. As in, use the AC to heat up the whole apartment, and that would dry the air out? We could try that too.

      • Yes, heating mode would work. Anything above ambient anyway.

        After reading through everyone's comments and your responses, maybe just aim to get out of the place when it's doable. At this point it sounds unhealthy and it's taking up your time and energy to remedy.

        Ventilation and drainage, you learn about it by force, then you live by it, and you never forget about it.

  • +1

    Moulds act in three stages primary, secondary and tertiary. Primary are ok as they are chill. Secondary are starting to compete for resources with primary and start to produce defence mechanisms to further their growth. Let mould grow and bam, you'll get tertiary growth. These are the really bad ones that fight all other types of mould for domination, releasing mycotoxins and VOCs that can have a serious effect on your health!

    Solution: Get rid of the water! Get rid of the mould….all of it…everywhere you can get to.

    Condensation will form on cool surfaces (windows at night) from moisture that you've vapourised during the day (cooking, breathing, showers etc).

    Ventilate, ventilate ventilate. Clean any visible mould with a microfibre cloth and mild detergent in water. Use vinegar if you want. Bleach is toxic and can damage surfaces.

    • +1

      Do you know anyone with a thermal IR camera (serious question)? As these things can detect water leaks through plaster walls and will allow you to detect areas that may have unseen damage.

      • Hm, no I don't know anybody. But some mould inspection websites claim they'll come out with a thermal IR camera. It's a brand new building though, so I'd hope there wouldn't be any water leaks?

        As for the mould, yes we've been trying to clean it all away (using vinegar or specific mould products), but I worry that if I just put everything back into the wardrobe again, it'll just get mouldy again and need forever to wash it all over etc.

        Just to be clear, we do not have any condensation anywhere. All windows and sliding doors are open all the time now, but still mysteriously have high humidity. :/

        • +3

          If you get a professional in please make sure they are accredited (e.g. certified Indoor air quality professional or an occupational hygienist (you can find them here:

          Make sure they test according to these standards:

          If they don't have a clue about iicrc standards then walk away, as they will not know what they are talking about.

          • @imnotgoingtopayrrp: Amazing - thank you. I'd looked up a ton of mould inspecting/cleaning companies and hadn't heard of this accreditation at all!

            • @kyttiekat: Plenty of cowboys out there. Beware of the "fogging" deep clean solutions, this is as effective as snake oil.

  • +2

    Some apartments are poorly designed/built and are prone to mould problems regardless of how the apartment is treated. You may not be the problem

    • +1

      I agree with this. I had rented 3 bedroom apartment while back and found out that this mold thing started happening at the beginning of winter which worsened so much. After talking with another apartment neighbor, they told same thing. When mold inspectors were called to inspect they said same things poor design of apartment to flow moisture vapor, therefore, condensed during winter forming mold on the ceiling.

      • Thanks for sharing! Were you seeing actual condensation on the ceiling that caused the mould? We aren't seeing any condensation anywhere thankfully. Also, our mould problem was growing like crazy while it was still summer in Feb and March.

        • Yes, After the inspector told about condensation and how moisture vapor is not flowing as it should be, I then noticed that in the morning there would be water condensed at the ceiling. I then tried to clean condensed water daily in morning for a week and there was a noticeable reduction. But after a few weeks, it would come back. Sigh, have to leave the apartment within the first year of rent. I would say, either use mold cleaner that could be bought from COLES or in your case( as this is your apartment) seek for proper mold inspector/cleaner.

    • Thanks. That could be it - bummer. Any ideas what would be best to remedy it?

    • The key mould sources in homes are usually: bathroom (exhaust fan not drawing sufficiently or venting into ceiling space rather than outside), laundry (clothes dryer condense moisture, especially older models, if you don't have a duct to outside), windows (dampness can come in from outside and condense on the inside of the window as the temperature changes throughout the day), plumbing leaks (this could be inside a wall or under the floor, or from the apartment above, harder to diagnose without a professional).

      Leaving windows/doors open all day only works in dry months — humid months in the southern states are highest from March to October, so check the weather websites to see what the worst months are. It will be often higher overnight, but rainfall affects it also — if you have your windows open during those periods, your dryer house can draw in more moisture from outside. Temperature differential has the biggest effect on airflow, so in combination with exhaust fans you can blow the damp air out, if you have open windows, but close up when you switch of the fans.

      Air-conditioning doesn't work the way most people think — Most aircon systems just recirculate the indoor air, they don't bring in fresh air from outside, which is why you need windows for ventilation (there are more expensive high-end fresh air HVAC systems but they're still rare in Australia).

      If you have a wall-mounted split system, it will only help dry the air in one room, if you have ducted A/C, you can dry the whole house — it doesn't really matter if it's set to heating (reverse cycle) or cooling, but warmth in winter and coolth in summer will be more effective due to the temperature differential, as long as there is some ventilation (windows opened a little).

      If you have evaporative cooling, don't use the cooling option, just the fan option — evap. will make the mould far, far worse by feeding the mould.

      One last thing: forget the DampRid and buy closet dehumidifiers for every space that you find damp / mould,
      Once you work out the main source(s) of the moisture, if it's plumbing issues get a plumber, if not get an electric dehumidifier, which can dry whole rooms out in hours.
      Also, spraying with a Borax-water mixture can be useful for killing and innoculating against mould on porous surfaces.

      It might sound like a big cost but the health cost is far higher if your family gets serious respiratory problems.

      • Thanks so much for your detailed post! Very helpful.

        We have ducted AC so we've been using that on 'dry' mode, and occasionally leaving windows open, but it doesn't seem to help. Humidity meter still reads 67% most days.

        I guess we need to call a professional to help us find the source… perhaps it really is just the construction of the building?!

        I've never seen those Daiso dehumidifiers - they're definitely cheaper than Damprid! Might have to give them a go as well.

        Many thanks again.

  • +1

    This is pretty much all new buildings that are constructed to be sealed rooms. People generate moisture. They generate it when they're washing, when they're cooking, even the very act of breathing adds moisture to the air, and all that moisture has to go somewhere. Either you design buildings the old way (very drafty) or you incorporate some form of moisture removal system.

    OP, try a portable air conditioner. You could put one in the middle of the room on the dry function, and it would extract moisture from the air. Because the hot air that's blown out the back stays in the room, it would have end up heating the room.

    Goal would be to get it to 50% humidity or lower

    • +1

      Or a de-humidifier. We've got a little Kogan unit at work and it works great.

      • They add too much cold air to the room/property IME. Okay for summer though, but usually not needed during those months of the year.

        • +2

          No, they don't. De-humidifiers and portable ACs work the same way, they don't 'create' cold, they just separate it from what's already there. If they aren't exhausting air to the outside, then they won't make the room any cooler overall. In fact, because they consume energy and that has to go somewhere, they should end up heating a room.

          • -2

            @outlander: I have two 20L dehumidifiers, they certainly do cool more than they heat.

            • +3

              @Bamboozle: Your argument isn't with me, sir, its with physics

              • @outlander: I'm using them though… Try for yourself and see. Something about them overcomes any heat output. It's annoying but they do their job, so I'm not complaining.😅

                A normal portable AC unit on the other hand… They are hot boxes even though they're ventilated to outside air.

          They work well in warm climates: The compressor dehumidifier has to be colder than the surrounding indoor air in order to work effectively so in warm climates, they are highly effective in getting rid of the moisture from the air. They are generally recommended for temperatures above 15°C.
          Because the compressor humidifiers reheat the de-humidified air back to the room temperature before blowing it back into the room, they can be great for environments where the room temperature needs to be maintained such as in wine cellars. However, they don’t “re-heat” the air by much. Usually, the compressed air is just 1°C to 2°C warmer than the ambient room temperature.

          Highly effective as dehumidifiers in spaces with high humidity at low temperatures. As a result, with the desiccant dehumidifiers, you don’t have to grapple with the 15°C “cut-off” room temperature for optimal performance that is required for the compressor dehumidifiers.
          They can keep your home warm during winters: While both dehumidifiers warm the air that passes through them before releasing it back into the room, they differ in terms of the degree of heat generated. The desiccant dehumidifiers offer a superior performance in this regard in that they offer a better heating performance. In the compressor dehumidifiers, the dry air being pumped out will be about 2°C warmer while in the desiccant dehumidifier, the dry air coming out will be about 3° to 5°C warmer. If you are looking for a dehumidifier for use in a chilly room or cold weather, the desiccant type would make perfect sense. In a warm room or warm weather where you may wish to maintain the same room temperature, you can go with the compressor type.

          • @Krzytofferz: Great info here!

            We ran our AC on 'dry' mode (which I understand is similar to a dehumidifier), and it cooled the place down dramatically - too cool! When we set it at a higher temperature, it just stopped being effective.

            Perhaps we need to look into a desiccant dehumidifer, in that case.

            Learning lots here, thanks!

  • Not sure about mould, but if you want to get rid of humidity you can do it with your reverse cycle air conditioning in 2 steps.
    1)Cool down the room at the lowest temperature yor AC will manage to get it. You do not need to be in the room. That will remove all the moist from the air.
    2)Without opening any windows set the AC to the highest temperature and get the room as hot as the AC will manage.
    Now you have the driest air possible.
    It is a waste of electricity, but that is how they dehumidify air for operating theatres in hospitals.

  • -1

    OK had that issue a few years back, here's what I did./ Got myself one of those 10 litre garden sprayers and some oil of cloves, you only need about 1 teaspoon per litre. Then I spray everything in the house, wall, ceilings and let the mist fall to the carpet, no problems. The leave it alone for 24-48hours, then any visible mould that was left I removed with a soft rag and some bleach in warm water. Mould hasn't come back and we get VERY humid time up here. I also bought a dehumidfier from Ausclimate and when things start getting moist I run that. But seriously, anything with mould on it, just hit it with oil of cloves diluted in water.

    • +1

      be careful - some research shows this isn't a good idea:
      She says you should "address the source of the moisture – excessive condensation, inadequate ventilation, inappropriate drainage, plumbing or roof leaks, flooding, high humidity and so on" first.

      • Well I did what I wrote above and haven't had any mould back since 2013.

  • -2

    An ozone generator kills moulds, but you do not want to be in the house while it's running or for a few hours after.

  • +1

    Not an expert except for sharing a similar issue. Being a huge geek I have temperature and humidity sensors in several places. It’s taken us about six years to learn to better manage the issue in a house in a rainforest valley. There’s a few things to keep in mind:

    1. You can’t reduce the humidity in the whole world, hence damprid or dehumidifier is useless if windows are open.
    2. Temperature changes can result in condensation inside, so for example first thing in the morning your indoor “normal” humidity can condense on walls or windows that are a few degrees cooler. Ie. At the dew point.
    3. Vinegar does work as a cleaner, plus there are paint additives that can help if you have a wall that’s a constant source of problems.
    4. Dehumidifiers add a small amount of heat to the environment, which isn’t unwelcome at this time of year, and can be effective within a closed environment.
    5. Humidity and temperature are inversely related, so as the temp in your room lowers, the humidity increases.

    So I’d recommend damp rid in any problem wardrobe, and if the problem is big then buy the bucket-sized ones. Keep the wardrobes closed. Add one or more dehumidifiers but there isn’t any point running them unless the room is closed. (See point 1). If the outside humidity is low and temp is high, open windows and turn off the dehumidifier. And try to ensure minimal internal temp changes to keep condensation to a minimum.

  • A dehumidifier helps to an extent. I've had this problem while I lived in a ground floor apartment with no proper ventilation. Had to use mould killers every 45 days or so. Bought a dehumidifier, turned it on every night before I go to bed, and in the morning, I could see it collected almost 2-2.5L of moisture(water). Resulted in using mould killer less frequently, but yes, I still had to use it. Some buildings are like this I suppose. The low quality paint on the wall could add to the problem and may help the mould spread fast.

  • Paint the house with this Protite Mould Defender Paint Additive
    This is banned in Canada, if a substance is banned you know it's the good stuff.

    Or you can paint the house with paint formulated for showers and bathroom ceilings. These paint loaded with good stuff to prevent mould.

    • Thanks! Useful to know. We have just moved in and it's brand new though, so not too keen on painting. Also, we don't have mould on any walls or ceilings etc… clothes, handbags, backpacks and books are a different story though!

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