It turns up in the same few places every winter. The top corner of a bedroom wall, the strip of ceiling above the shower, the patch of plaster behind the wardrobe on the cold side of the house. You wipe it off, feel like you've dealt with it, and six weeks later it's back in exactly the same spot. Getting rid of mould on walls is really two jobs rather than one: killing what's there, and changing whatever keeps growing it. Most people only ever do the first.
Here's the short version, then the detail.
Open the windows, put gloves on, and wet the mould before you touch it, because dry-scrubbing flicks spores across the room. On painted walls, Tenancy Services recommends white vinegar diluted half and half with water so it doesn't damage the paint. Leave it for a few days, then wipe the dead mould off with soap and water using a clean cloth. Diluted bleach at one part bleach to three parts water is the alternative, and you must never mix the two. Then deal with the moisture that put it there. Mould needs damp to grow, so if the damp doesn't change, neither does the mould.
Why it's on your wall in the first place
Mould isn't dirt. You can keep a spotless house and still get it, which is part of why it feels so unfair when it shows up.
Spores are in the air everywhere, all the time. They only become a problem when they land somewhere that stays damp long enough for them to grow. As BRANZ puts it, visible mould in houses is typically the result of high indoor moisture combined with not enough ventilation or heating.
In a New Zealand winter you can build those conditions without doing anything wrong. Warm, moist air from showers, cooking and drying washing meets a cold exterior wall and condenses onto it. Consumer NZ puts a single load of washing dried indoors at around five litres of water released into the house. Do that twice a week in a home closed up for July and the walls are where it ends up.
That's why it appears in such predictable spots:
- Cold exterior walls, worst in the corners where two cold surfaces meet
- Behind furniture pushed flat against an outside wall, where no air moves
- Inside wardrobes on an exterior wall, for the same reason
- Above the shower and along the ceiling line, where the extractor fan is weak or vents nowhere
- Around window joinery, which we go into in our window cleaning guide, since aluminium frames and their rubber seals collect condensation and hold it
Which is worth understanding before you start scrubbing. The mould is a symptom. The wall is telling you something about the room.
How to get rid of mould on walls
On a small patch this is absolutely a job you can do yourself. Work in this order.
- 1. Open up and protect yourself. Windows open before you start, gloves on, and a mask if the patch is more than a small one or anyone in the house has asthma or allergies.
- 2. Wet it. Never scrub it dry. Dry-brushing or wiping with a dry cloth flicks spores across the room and seeds the next patch somewhere else. Everything from here is done wet.
- 3. Mix your solution. White vinegar diluted half and half with water on painted surfaces. The dilution matters, because neat vinegar can lift the paint finish along with the mould.
- 4. Leave it to work. Tenancy Services says to leave it for a few days rather than wiping straight off. It needs contact time to kill the growth, not just move it around.
- 5. Wipe off the dead mould with soap and water. Clean cloth, warm soapy water, rinsing or swapping cloths as you go so you're not carrying spores back onto the wall you just did.
- 6. Dry the surface properly. Wipe it dry, then keep the room aired and warm for a few days. A surface left damp is an open invitation.
- 7. Deal with the cloths. Bin them, or wash them separately on a hot wash. A mouldy cloth back in the cupboard undoes the job.
Grout and silicone are a harder fight, because the growth gets into the material rather than sitting on top of it. Consumer NZ is blunt that mould in grout and silicone is close to impossible to remove completely and often needs replacing. Sometimes the honest answer on old silicone is that no amount of scrubbing will bring it back.
Never mix bleach and vinegar. Consumer NZ is explicit that combining them creates toxic chlorine gas. The same goes for mixing bleach with ammonia or any other cleaning product. Pick one, use it on its own, keep a window open, and wear gloves.
Bleach, vinegar, or something else
This is the argument you'll find online, and the answer is less dramatic than either side makes out.
Tenancy Services lists both. White vinegar first, described as cheap and effective, diluted half and half on painted surfaces. Diluted household bleach second, at one part bleach to three parts water. Either is legitimate.
Where bleach catches people out is that it's very good at removing colour. A patch goes pale and looks dealt with while the surface underneath hasn't really been sorted, which gives you a false read on whether it's gone. That's the main reason we'd reach for vinegar on a painted wall, along with not wanting bleach fumes in a closed-up bathroom.
The bigger point is that the product is the least important part of this. You don't need a specialist spray, and you don't need us. A patch in the corner of a ceiling is a supermarket bottle of vinegar and a bit of patience. What kills mould long-term is a drier, warmer, better-ventilated room, and no product fixes a wall that's cold and wet every night.
Painting over it. It happens constantly in rentals and in houses being tidied up for sale, and it never works. Paint doesn't kill mould, so it carries on growing underneath and comes back through the new coat within months, usually looking worse and now with a paint job to redo as well. Kill it, clean it, get the surface properly dry, then paint if you want to. Mould-resistant paint is a finish, not a treatment.
Why it keeps coming back
If it returns to the same spot within a few weeks, cleaning was never going to be enough. Something about that surface is keeping it wet. The usual culprits, roughly in the order we see them:
- No extraction, or extraction that goes nowhere. A bathroom fan venting into the ceiling cavity instead of outside is just moving the problem upstairs.
- Washing dried indoors. Litres of water per load, released into a house with the windows shut.
- Unflued portable gas heaters. Tenancy Services advises using an electric heater instead, because portable gas heaters release water as the gas burns.
- Furniture hard against exterior walls. It stops the air moving and makes the coldest surface in the house colder still.
- A house that's never properly warm. Cold surfaces plus moist air equals condensation, every time.
- An actual leak. A blocked gutter, a failed downpipe, or water getting in somewhere. This one won't respond to ventilation at all.
Keeping it off through a New Zealand winter
You don't need to change how you live. You need to change what happens to the moisture you're already making.
- Run the bathroom fan through the shower and for a while afterwards, rather than switching it off with the light.
- Open the house up for fifteen or twenty minutes a day, even when it's miserable out, and open the curtains so the windows get some sun.
- Wipe condensation off window channels and sills on cold mornings, before anything gets a start.
- Pull wardrobes and drawers a few centimetres off exterior walls so air can move behind them.
- Lid on the pots when you're cooking, and dry washing outside when you can. If it has to come inside, put it in one room with the door shut and a window cracked.
- Keep the house warmer. Warm air holds moisture instead of dumping it on cold surfaces.
- Check the outside. Blocked gutters, a downpipe running onto a wall, and garden beds banked up against the cladding all push moisture into the building.
None of that is glamorous, and all of it works better than the next bottle of spray. A regular clean keeps the surfaces on top of things, but ventilation and heating are what stop the mould forming at all. If you're setting a wider rhythm for the house, our guide on how often to clean your house has the winter jobs built into it.
When it's not a cleaning job
Here's the part that costs us work, and it's worth saying plainly.
Condensation mould sits on the surface, appears in cold spots and corners, and cleans off. Mould driven by water getting in behaves differently. MBIE treats visible mould spreading across walls and floors as a signal of a weathertightness problem rather than a cleaning one, and BRANZ notes that the species people worry about are generally caused by leaks originating outside the building or within wet areas.
Signs it's the building and not the housekeeping:
- It's back in the same place within weeks of a proper clean
- It's in the middle of a wall or ceiling rather than in a cold corner
- There's a tide mark, blistered paint, or plasterboard that feels soft
- There's a musty smell you can't trace to a visible patch
- It appears after rain rather than on cold mornings
Tenancy Services notes that a qualified building surveyor may need to check the property for a hidden issue causing the dampness. For extensive mould, MBIE advises seeking experienced advice on removal.
If the cause is a leak, a drainage fault or a subfloor that stays wet, cleaning the wall changes nothing that lasts. We'll treat surface mould as part of a deep clean, and we'll tell you when what you've got is beyond a clean. Paying a cleaner to wipe the same wall every winter is money going nowhere. That one's a builder, a plumber or a surveyor, not us.
On health, it's worth being measured rather than alarming. MBIE notes that problems can arise when large numbers of spores are inhaled, ingested or come into contact with skin, listing allergic reactions, aggravated breathing, eye and skin irritation and headaches, with the greatest risk to people with asthma, weakened immune systems, infants and older people. That's a reason to deal with mould promptly. It's not a reason to panic about a spot in the bathroom corner.
Where the whole house has got away on you, that's a different job to a patch on a ceiling. A deep clean resets it, and our guide on regular versus deep cleaning explains where that line sits. Once it's back to a good baseline, a regular house clean is enough to hold it there. If you're selling, deal with it before the photographer rather than after, because buyers read mould on a window seal as evidence about the house rather than about the cleaning. That's part of what a pre-sale clean is for, and our pre-listing checklist goes through the rest.
If you're renting
Mould in a rental has rules attached, and they cut both ways.
Your side. Once you move in you need to keep the place clean and tidy, and Tenancy Services is clear that a well aired, ventilated house is crucial to preventing mould. In practice that's the winter routine above.
Your landlord's side. The property should be free of mould and dampness at the start of the tenancy, and the landlord is responsible for the building itself: clear gutters, working downpipes and drainage, and a ground moisture barrier in an enclosed subfloor where that's reasonably practicable.
The healthy homes standards. These set minimums for heating, insulation, ventilation, moisture ingress and drainage, and draught stopping. The ventilation standard requires openable windows, doors or skylights in the living room, dining room, kitchen and bedrooms totalling at least 5% of that room's floor area, plus extractor fans venting outside in kitchens and bathrooms. Tenancy Services states that all private rentals had to comply by 1 July 2025. Compliance rules do change, so check the current position on their site before relying on it.
If you're doing the right things and it's still damp, that's a conversation with your landlord, in writing. A persistent problem usually has a cause a tenant can't fix.
If you're moving out and there's mould to sort before the final inspection, our bond-back guide covers the standard you're actually held to, and an end-of-tenancy clean includes treating mould on grout and silicone as part of the job.
General information about cleaning and tenancy obligations only, not legal or medical advice. Tenancy rules and healthy homes requirements can change, so check tenancy.govt.nz for the current position, and talk to a doctor if anyone in the house is unwell.