Mould on Walls and Ceilings in Auckland: Fix the Damp Before You Paint

Can you paint over mould?

No. Paint over live mould and it can grow back through the new coat, and the stains underneath often bleed through as well. Even a paint with a mould inhibitor only slows new growth on its own surface; it does nothing about the moisture that fed the mould in the first place.

So the order matters: find and fix the damp, kill and remove the growth, let the surface dry right through, seal any staining, then repaint. Skip a step and you are usually looking at the same spots again next winter.

Why do so many Auckland homes get mould?

Because Auckland's mild, humid climate keeps a lot of moisture in the air, and in winter that moisture condenses on the coldest surfaces in the house. Single-glazed windows, outside walls, ceilings under poorly insulated roof spaces and the corners where they meet all stay cool and damp, and wherever a surface stays damp for long enough, mould can grow.

Everyday life adds the moisture:

• Showers and baths in a bathroom without a working extractor fan.
• Cooking without a rangehood that vents outside.
• Drying washing indoors.
• Unflued gas heaters, which release water vapour as they burn.
• People breathing in closed-up bedrooms overnight.

Shaded rooms, and homes on bush-clad or steep sections like those you'll find in parts of West Auckland and the North Shore, dry out more slowly, so they tend to see more of it.

Where does mould usually show up?

On the coldest, dampest and least ventilated surfaces:

• Bathroom ceilings, especially above the shower.
• Bedroom corners where outside walls meet the ceiling.
• Behind wardrobes, beds and drawers pushed against outside walls.
• Around window frames and reveals, where condensation runs down.
• Laundries, and rooms that are closed up and rarely heated.

Where it shows tells you a lot about the cause. Spots spread across a cold corner or a ceiling usually point to condensation. A patch that grows after heavy rain, or sits under a window, a roof junction or a pipe, points to water getting in.

Is it condensation or a leak?

Condensation mould tends to appear in winter, on cold surfaces, often in several rooms, with no sign of water coming in. Leak mould usually comes with staining, tide marks, bubbling paint or soft plaster in one area, and it gets worse after rain.

Signs it is condensation

• Water beading on windows most mornings.
• Mould in corners and across ceilings rather than one patch.
• Worse in winter, better when the house is heated and aired.

Signs water is getting in

• Brown or yellow staining and tide marks.
• Bubbling or peeling paint, or soft, swollen plasterboard.
• A musty smell that stays after cleaning.
• Patches below windows, at roof junctions, or on walls with plumbing behind them.

On plaster and monolithic homes, staining inside near windows or at the base of walls can also mean water getting into the cladding. Our page on painting plaster homes lists the warning signs, and why a building surveyor should look first.

What needs fixing before the painting?

Whatever is feeding the mould. Paint is the last step, not the fix.

• Leaks repaired first, by the right trade: a roofer, plumber or builder.
• A bathroom extractor fan that vents outside, not into the ceiling space, used during and after every shower.
• A rangehood that vents outside, and lids on pots.
• Washing dried outside or in a vented dryer.
• Regular airing and steady heating, especially in bedrooms.
• Furniture moved a little away from outside walls so air can move behind it.
• Ceiling and underfloor insulation checked if the house has little or none.

None of this is glamorous, but it decides whether new paint stays clean for years or spots again in the first cold spell.

How should mould be cleaned off before painting?

Kill it, remove it and let the surface dry fully. Use a mould treatment made for painted walls and ceilings, and follow its label for dilution, contact time and rinsing.

• Ventilate the room and cover floors and furniture.
• Wear gloves, eye protection and a suitable mask.
• Do not dry-brush, scrape or sand mould: that spreads spores through the house.
• Never mix cleaning products. Bleach with ammonia-based cleaners, for example, gives off dangerous fumes.
• Let the surface dry right through before any primer goes on. Painting a damp surface traps the moisture in.

Household bleach can lighten the stain without dealing with growth in porous surfaces such as the paper face of plasterboard, so a product made for mould is the better choice. Keep children, pets and anyone with asthma or allergies out of the room while it is treated.

When is a mouldy wall or ceiling past painting?

When the lining itself is damaged. Plasterboard that is soft, swollen, sagging or crumbling, mould on the back of wallpaper or inside the wall, and mould that returns within weeks of cleaning all mean the problem is behind the surface.

Damaged board usually needs cutting out and replacing, often by a builder, once the leak is fixed and the framing has dried. Firm board with surface staining can usually be treated, spot-primed with a stain blocker, repaired and repainted; our section on plaster repairs explains how.

If mould covers a large area, keeps coming back, or someone in the house has health concerns, have the moisture problem investigated by a building professional before any painting.

Which primer and paint help stop mould coming back?

A stain-blocking primer over any marks, then finish coats of a paint made for kitchens and bathrooms. These usually contain a mould inhibitor and stand up to steam and wiping better than general wall paint.

Sheen matters in wet rooms. A low-sheen or semi-gloss finish sheds moisture and wipes clean more easily than flat paint, so wet-area paints usually come in those finishes rather than flat. We use Resene, Dulux and Wattyl paint systems, and our written quote names the primer, the finish and the number of coats for each room.

An inhibitor slows mould on the paint surface, but it cannot keep up with a room that stays wet, so the fixes above still matter.

How do you keep a repainted bathroom ceiling free of mould?

Get the steam out quickly. Run the extractor fan during every shower and for a while afterwards, open the door or window once you are done, and wipe away water left on the ceiling or walls.

Give new paint the drying time the manufacturer specifies before the first hot shower, because steam on fresh paint can leave streaks and marks. If the ceiling still grows mould with the fan running, the fan may be too weak or not ducted outside, or the ceiling may be cold because of missing insulation.

What about bedrooms, wardrobes and outside walls?

Warmth and air movement are the fix there:

• Pull wardrobes, beds and drawers a little away from outside walls.
• Leave wardrobe doors ajar in winter, and do not pack them tight.
• Wipe window condensation each morning and keep sills and frames clean.
• Open curtains and windows during the day, and keep the room heated in winter.

Mould that comes back in the same corner every winter marks a cold spot. A paint made for damp rooms helps, but warmth, airflow and insulation are what stop it. If you are planning a repaint, our checklist for preparing your home for painters covers clearing rooms and furniture.

Is mould on outside walls handled the same way?

Mostly, yes: kill it, wash it off and let the surface dry before any paint. Outside, mould and mildew grow on shaded south walls, under eaves, and on walls beside trees, banks or fences that keep them damp.

It is treated with a cleaner that kills it, then washed off. On plaster and texture-coated walls the wash is done at low pressure, because a high-pressure blaster can force water into cracks and behind the cladding. Our guide to exterior painting preparation covers the full wash and repair sequence.

How should landlords deal with mould between tenancies?

Fix the cause, then paint while the house is empty. It is far easier to treat, dry and paint rooms without furniture and tenants in the way, and a clean, dry, ventilated room gives the new paint its best chance. Rental homes also have to meet the Healthy Homes standards, which include ventilation and moisture requirements, so dealing with the cause is part of the job.

We paint rentals for landlords and property managers; see professional painters for property managers for how we plan work around tenancies.

How do we quote a mouldy room?

After a free site visit. We look at the mould, the staining and the surfaces, tell you plainly if something needs another trade first, and give you a written fixed quote that lists the treatment, repairs, primer, paint system and coats for each room.

For typical ranges on a whole interior, see painting costs in Auckland, where the cost calculator gives an indicative budget from your own measurements. Our interior painting page covers the rest of the process, and we reply to every enquiry within two business days.