Mould questions answered

Causes in humid homes

Why does mould grow?

Most mould at home starts with moisture that has nowhere to go. Spots that stay damp, such as bathroom corners, the back of a wardrobe or a room kept shut, give it time to grow. Poor ventilation, condensation and leaks add moisture, so cleaning alone may not stop it. NEA says opening doors and windows can improve home ventilation.

Where should I look for mould?

Look where moisture stays and air does not move: bathroom ceilings, corners and grout, the cabinet under the kitchen sink, behind furniture pushed against a wall and inside wardrobes. Take a closer look at a ceiling below a neighbour's bathroom. HDB says ceiling leaks typically occur in toilets and bathrooms.

How can a ceiling leak cause mould?

Water from the flat above can seep through the floor slab when the waterproof membrane and screed wear out. HDB says this is common in older buildings, that untreated leaks may damage electrical items and cause mould growth, and that neighbours should address a leak promptly. Recurring ceiling mould is worth checking with your upstairs neighbour.

Can mould grow inside an aircon?

Yes. Mould grows where moisture stays, and an aircon handles humid air every time it runs. Cleaning inside a unit is a different job from wiping tiles or walls, and some parts are out of reach. Our guide to mould in an aircon covers what you can safely clean yourself and when to call a servicing company.

Mould removal and prevention

How do I remove mould from bathroom surfaces?

For small patches on tiles, grout or walls, use a cleaning product suitable for mould and follow its label. NEA's guidelines for cleaning residences say to clean bathrooms from high to low (wall to floor) and from cleaner to dirtier areas (shower to toilet bowl). If the whole bathroom needs attention, a deep cleaning service may suit you better.

How can I improve ventilation?

Moving air helps damp surfaces dry. NEA's guidance on ventilation and indoor air quality says you can improve home ventilation by opening doors and windows, and use fans to promote air circulation when needed. Rooms kept shut for long periods, such as a storeroom or spare bedroom, and bathrooms after a shower are good places to start.

How do I use cleaning products safely?

NEA's residential cleaning guidelines say to prepare and apply disinfectants according to the manufacturer's guidelines, leave them for the stated contact time and use the protective equipment the product's Safety Data Sheet prescribes. NEA lists household bleach as the most widely used disinfectant and notes that hypochlorites are fungicidal. Follow the label for dilution. Use one product at a time and never mix bleach with other cleaners, especially acid-based or ammonia cleaners, as the fumes are harmful.

Can cleaning habits help prevent leaks?

Yes. HDB's ceiling leak guide suggests using non-corrosive detergents in toilets and bathrooms, and mopping the kitchen floor instead of washing it, because there is no waterproofing membrane under kitchen tiles. It also suggests a sink strainer, and not putting food waste down the sink. Fewer leaks mean fewer damp ceilings in the flat below.

Health and when to call help

Can mould affect my health?

Some people may be more sensitive to mould, including people with asthma or allergies. If you are worried about a mould allergy or symptoms at home, see a doctor. This page is general information, not medical advice. Meanwhile, deal with the damp source and keep rooms aired. Our guide to mould on the ceiling covers cleaning small patches safely.

When should I call a cleaner?

Consider a professional deep cleaning service when mould covers a large area, keeps coming back after you clean, or sits somewhere you cannot reach safely, such as a high ceiling. Recurring mould is also a sign to look for a moisture source, because a cleaner removes the growth, not the leak or damp behind it.

When is it a job for a contractor?

Suspect a leak if the ceiling stays damp or mould returns soon after cleaning. For a leak between two flats, HDB's steps are to talk to your upstairs neighbour, agree a time for a check and engage a contractor jointly. The contractor confirms the source and recommends a repair method. Who arranges and pays depends on where the leak is.

Where to go next

Most mould problems need two things: cleaning what you can see and fixing the moisture behind it. These pages go deeper:

• Mould on the ceiling: why it forms, signs of a leak and how to clean small patches.
• Home cleaning: companies with their published prices and the areas they say they cover.
• Home cleaning prices: published rates by type of service, each linked to its source.

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