Repair and fix mould covered walls in Hong Kong

Our apartment is plagued with mould and we need to have the whole flat repainted. What Is the best type of paint to use to stop it reappearing and what should we use to treat the affected surfaces before we paint?

Before doing anything you could try washing the walls and ceiling with diluted bleach and leaving them to dry overnight. You could then apply a water-based fungicide treatment from Permaglaze (HK$70 per tin from hardware stores) using a spray brush or roller: again, let it dry overnight. When it comes to repainting, there are several products available that have strong mould resistant properties. Levine Mouldshield is a mould-resistant gloss emulsion paint (HK$70 per litre or HK$260 for four litres), available from most good hardware shops. It is designed to prevent mould forming on interior walls and ceilings. It is hard wearing and has a finish suitable for surfaces cleaned regularly. Dulux's Supreme range offers a premium low-sheen emulsion with excellent mould resistance. It costs HK$80 per litre or HK$340 for five litres, and has similar properties to the above.

Visit your local hardware store for a full range of mould-resistant paints.

Why Is Mould So Common in Hong Kong Homes?

After nearly 30 years of tackling mould problems in Hong Kong apartments, I can tell you without hesitation that this city is one of the toughest places in the world when it comes to keeping mould at bay. There are very specific reasons for this, and understanding them is half the battle.

Hong Kong's subtropical climate means that from roughly April through September, outdoor humidity regularly exceeds 80-95%. During the spring "return moisture" period (typically March to April), warm, moist air meets cool wall surfaces that have been chilled all winter, and condensation forms on everything. You will see water literally running down walls and pooling on floors. This is perfectly normal for Hong Kong, but it creates ideal conditions for mould spores to germinate and spread.

The problem is compounded by several factors specific to Hong Kong living:

• Small, enclosed spaces with limited ventilation: Many Hong Kong bathrooms have no windows at all, relying entirely on small exhaust fans that are often undersized or poorly maintained.
• Air conditioning usage patterns: When you run the AC in one room but not the bathroom, you create a temperature differential that drives condensation onto bathroom walls and ceilings.
• Older buildings with poor insulation: Many buildings from the 1960s-1980s have concrete walls with no insulation or vapour barrier. These walls absorb moisture like a sponge.
• Drying clothes indoors: In a city where many flats have no outdoor drying space, hanging wet laundry inside adds enormous amounts of moisture to the indoor air.

Mould is not just unsightly. It is a health concern, particularly for children, elderly residents, and anyone with respiratory conditions like asthma. If you can see mould, you need to deal with it promptly. And if you can smell that distinctive musty odour but cannot see mould, it may be growing behind furniture, inside wardrobes, or behind wall coverings.

How Do You Prevent Mould from Returning?

Treating mould is only half the job. If you do not address the underlying moisture problem, the mould will return within weeks. Here is what I tell every client:

• Invest in a good dehumidifier: This is the single most effective weapon against mould in Hong Kong. A decent dehumidifier with a 12-20 litre daily capacity costs HK$1,500-3,500. Brands like Mitsubishi, Panasonic, and Sharp are widely available at Fortress, Broadway, and PriceRite. Run it daily during the humid months and you will be amazed at how much water it pulls from the air. Empty the tank regularly or connect it to a drain hose.
• Upgrade your bathroom exhaust fan: A properly sized exhaust fan for a typical Hong Kong bathroom (3-5 square metres) should move at least 80-100 CFM of air. Many installed fans are far weaker than this. Replacing a weak fan costs HK$300-800 for the unit plus installation. Run it during and for at least 20 minutes after every shower.
• Use anti-mould paint: As mentioned above, products like Levine Mouldshield (HK$70-260) and Dulux Supreme (HK$80-340) contain fungicides that actively resist mould growth. For ceilings and areas above the shower, these paints are well worth the investment. Apply two coats for best results.
• Seal gaps around windows and pipes: Check for any gaps where humid air can enter from outside or where water may be seeping through walls. Seal these with bathroom-grade silicone.
• Keep furniture away from external walls: Leave a gap of at least 50mm between wardrobes, beds, and external walls to allow air circulation. This is particularly important for north-facing walls which are the coldest and most prone to condensation.
• Open windows when weather permits: On dry, breezy days (common from October to February), cross-ventilation is the most natural and effective way to dry out your home.

For persistent mould problems on ceilings or in areas where paint alone is not enough, consider applying a specialist anti-mould coating from Permaglaze before repainting. This creates an additional barrier that standard paint does not provide.

If mould keeps returning despite your best efforts, the root cause may be water seeping through external walls or a concealed pipe leak. In older Hong Kong buildings, these hidden moisture sources are extremely common and no amount of surface treatment will solve the problem until the source is addressed.

When Should You Call a Professional?

A small patch of surface mould on painted walls is a straightforward DIY clean-up with bleach and repaint. But call a professional if:

• Mould covers more than one square metre: Large areas of mould, especially black mould, can release significant quantities of spores when disturbed. Professional remediation with proper containment and protective equipment is safer.
• Mould has penetrated the plaster or wall substrate: If the plaster behind the paint is soft, crumbly, or discoloured, the mould has gone deeper than the surface. The affected plaster needs to be removed and replaced before repainting.
• Mould keeps returning in the same spot: This almost always indicates an ongoing moisture source such as a hidden pipe leak, failed waterproofing, or structural condensation problem that needs proper diagnosis.
• You are renovating or selling the property: A professional mould treatment followed by proper anti-mould painting gives you a documented treatment history, which is valuable for refreshing the look of a property before sale or new tenancy.

Last updated: March 2026