Mould and humidity in Samui villas: what cleaning fixes and what it doesn't

Sooner or later, every house on Samui has to deal with mould. The air is warm and humid for most of the year, many villas stand closed for weeks at a time, and badly ventilated bathrooms never dry out completely. Mould needs moisture and something to grow on, and a tropical house provides both.

There are two very different situations. Surface mould grows on a surface because the air is damp. A thorough clean removes it, and good habits keep it away. Mould with a source grows because water keeps reaching that spot, whether from a leaking pipe, the roof, rising damp or condensation inside a wall. You can clean it today and it will be back in two weeks. That needs a repair, not more cleaning.

Knowing which kind you have saves both money and frustration.

• Year-round humidity. It peaks in the rainy season, roughly October to December, but it is rarely low at any time of year.
• Closed houses. With the windows shut and the AC off, moist air stays trapped inside. Wardrobes, drawers and bathrooms suffer first.
• Cold surfaces. When a room is cooled hard by the AC and the air outside is warm and humid, condensation forms on windows, on walls and around AC pipes.
• Bathrooms that never dry. A shower with no extractor fan or window stays wet for hours after use.
• Materials. Silicone, grout, unsealed stone, fabric and leather hold moisture and give mould something to cling to.

These are cleaning jobs, and in most cases the result lasts, provided humidity is the only cause:

During a deep clean, we remove surface mould from silicone, grout and tiles, clean the inside of empty cupboards and wardrobes, and wipe extractor fan covers. We choose products to suit each surface: acidic or strong cleaners that are fine on porcelain can damage marble and some other natural stone, so we ask if we are not sure.

• Mould that comes back in the same spot within a few weeks. Something keeps that area wet.
• Damp patches that spread after rain, on ceilings, below windows or at the bottom of walls. Check the roof, the window seals and the drainage.
• Bubbling paint, crumbling plaster or a soft wall. The moisture is inside the wall.
• Mould behind tiles or under the shower tray, often with loose tiles or a smell that will not go away. This usually means a leak or failed waterproofing.
• Silicone that stays black after cleaning. The mould has grown into it, and the only fix is to strip and replace the silicone, which is a job for a handyman.
• Mould inside AC units and ducts. That is work for an AC technician, not a cleaner.
• Mould that has gone deep into mattresses, sofas and curtains. These need specialist cleaning or replacing.

If we come across any of these during a visit, we photograph it and flag it in the photo report. We do not paint over mould, and we will never tell you that a clean has solved a leak.

1. Have the spot cleaned properly.
2. Photograph it the same day.
3. Look at it again after two weeks of normal use.

If it is still clean, or only a few small spots have come back in a room used every day, humidity was the cause, and better airflow and regular cleaning will be enough. If it is back in the same place and in the same shape, there is a source. Call a plumber, a roofer or your builder, and have it cleaned again after the repair.

• Keep the air moving. Open the windows when the weather allows, run extractor fans during and after showers, and leave bathroom doors open afterwards.
• Dry the air. A dehumidifier in closed rooms and wardrobes, or the AC's dry mode if it has one, makes a real difference. Empty the dehumidifier tank regularly.
• Leave gaps. Stand wardrobes and large furniture a few centimetres away from outside walls, so air can reach the back.
• Do not dry laundry indoors in rooms with no airflow.
• Dry the shower after use. Running a squeegee over the glass and tiles after each shower keeps the grout clean for longer.
• Store linen and clothes dry, in breathable or airtight boxes with moisture absorbers.
• Clean regularly. Caught as a few spots during a weekly regular clean, mould takes minutes to deal with. Left for months, it calls for a deep clean, or worse.

For a villa that stands empty, the best protection is regular visits to air the house, run the taps and check for damp. Our guide to villa care while you are away covers this, and the rainy season guide has a month-by-month checklist for the wet months.

If you tackle mould yourself, ventilate the room and wear gloves. Never mix bleach with acidic cleaners or ammonia, because the fumes are dangerous. Large areas of mould, mould that keeps coming back, or mould in a home with young children or someone with asthma are all reasons to call a specialist rather than scrub harder.

Removing surface mould is part of a deep clean. A deep clean of a 3-bedroom, 3-bathroom villa costs 5,000 ฿, and for a 1-bedroom condo prices start at 2,300 ฿. After that, regular cleaning keeps the mould under control: 2,040 ฿ per visit on a weekly schedule for the same villa. If a property is in a very bad state, we assess it from photos and agree the price before the visit, never on the day.

Every clean ends with a photo report. If we missed something on the checklist, tell us within 24 hours and we will come back and put it right free of charge. Read more about how we check quality.