The situation in Bangkok, late September 2026

According to news reports, continuous heavy rain of roughly 300 mm fell on Bangkok in about 48 hours between 24 and 27 September 2026. On 26 September the Bangkok Metropolitan Administration declared all 50 districts a disaster zone. Eastern Bangkok was hit hardest, with areas such as Khlong Chan and Bueng Kum mentioned in coverage. Governor Chadchart said the canals were full and that drainage would take two to three days after the rain stopped. Reports also noted three deaths, and our thoughts are with the families affected.

As of 30 September, some roads, including Si Burapha and Lat Phrao, still had 20 to 40 cm of standing water. Thai media compared the event with the 2011 floods, and one Thai business report cited a Chamber of Commerce estimate of about 12,300 million baht in damage. As the water recedes, thousands of condo owners are starting repairs at the same time, and one quiet problem follows almost every renovation: a smell that makes the unit very hard to rent.

A typical scenario (an illustrative situation, not a review from any specific customer)

A beautiful new room, and a tenant who left in under two minutes

Ton is a 38-year-old office worker who bought a ground-floor unit in a low-rise condo near Bueng Kum five years ago as a rental investment. The 30-something square metre room had always found tenants easily. Then the late-September rain came. Water from the street flowed into the car park and lobby, then seeped into the ground-floor units to about ankle height. The existing tenant moved out straight away: the appliances were damaged and nobody wants to live in a soaked room.

Once the water dropped, Ton hired contractors immediately. They ripped out the swollen laminate floor, cut away the lower section of wet gypsum wall, repainted every wall, replaced a built-in wardrobe made of particleboard that had puffed up so badly the doors would not close, laid a glue-down vinyl floor, re-sealed the bathroom with silicone, and brought in a new mattress and sofa to stage the room. He expected to have a new tenant within three weeks, right when many displaced people were looking for somewhere to live.

On the day the agent brought a young expat family to view the unit, the door had barely opened when a wave of thinner, glue and a faint musty dampness hit them. The mother covered her child's nose. They spent less than two minutes inside. That evening the agent called: "The room looks great, but they said the smell made their eyes sting and they were worried about the baby." Two more viewings the next week ended the same way.

Ton tried opening the window, placing charcoal bags in every corner, running an air purifier and spraying floral air freshener before each viewing. Yet every morning, when he opened the door of a room that had been closed overnight, the smell was back. Every empty month meant a mortgage payment, a common-area fee and lost rent. Ton's story is not unusual. It is happening again and again in ground-floor units and flood-affected condos across Bangkok during this post-flood renovation season.

Where the smell in a post-flood renovated condo comes from: three layers stacked together

Many owners assume the smell in a freshly renovated unit is simply "new paint" that will fade on its own. In a room that has just been flooded, what you actually smell is a mixture of three sources stacked on top of each other, and each behaves differently. Understanding them helps you choose a fix that targets the cause instead of paying again and again for products that only cover it up.

Layer one: floodwater and mud

Urban floodwater is not clean water. It carries sewage from drains, rubbish, silt and oily residue from roads and car parks. When it recedes, that residue stays in tile grout, under skirting boards, inside pipe openings, behind cabinets and inside porous materials. Decaying organic matter gives off a drain-like, sour smell that comes and goes, especially when the air is hot and humid and the room has been shut for a long time.

Layer two: dampness and mold

Public health agencies such as the CDC advise cleaning and drying within 24 to 48 hours after a flood to limit mold growth. In reality, many units had to wait for street water to drop, for contractors to be free and for electricity to be restored. That gave moisture time to soak deep into gypsum board, timber door frames and the sub-floor. Growing mold releases its own volatile compounds, the familiar "closed-up room" mustiness. Even after a fresh coat of paint, if the inside of the wall is still wet, the smell finds its way out.

Layer three: volatile organic compounds from the renovation

This is the layer owners overlook most, because it arrives with the new things they bought to improve the room. Wall paint, thinner, wood lacquer, flooring adhesive, wall adhesive, silicone sealant, epoxy, plywood, particleboard and MDF used for built-in furniture all release volatile organic compounds (VOCs) into indoor air. Well-known examples include toluene and xylene in solvents, and formaldehyde from the resins used to bond engineered wood panels.

These compounds do not all evaporate on day one. They off-gas over weeks or longer, depending on the material, the temperature and the ventilation. In a condo with few windows, kept closed because nobody is living there, and cooled by a split-type air conditioner that simply recirculates indoor air, VOCs build up to noticeably higher concentrations than in a room with a cross-breeze. That is exactly why the smell is strongest when you open the door in the morning.

Symptoms occupants and viewers commonly notice

Exposure to higher levels of VOCs in an enclosed space can cause irritation of the eyes, nose and throat, headaches, dizziness, nausea and tiredness, and in some people can trigger asthma or allergy flare-ups. Mold odour adds sneezing, a blocked nose, coughing or itchy eyes in sensitive people. Add residual drain smells, and the room feels "unclean" from the first second a prospective tenant walks in, even though everything looks brand new.

Who is most at risk

People who are especially sensitive to airborne chemicals include babies and young children, who breathe faster than adults and spend time close to the floor; pregnant women; older adults; people with asthma, allergies or chronic lung disease; and pets such as dogs, cats and birds. These are exactly the tenant groups common in the Bangkok rental market. Families with small children and pet owners are usually the first to reject a unit with a strong chemical smell. Anyone with persistent symptoms such as difficulty breathing, chest tightness, or fever after wading through floodwater should see a doctor promptly. This article is not medical advice.

What a lingering smell really costs a condo landlord

Money: every empty month is income you never get back

Most owners still pay the bank instalment, the common-area fee and insurance while the unit sits empty. On top of the renovation bill they just paid, a unit that will not rent because of odour becomes a double financial burden. If you have to cut the rent to attract someone, your return falls for the entire lease term.

Time: the post-flood rental window is short

After a flood, many people need temporary or permanent new accommodation. Units that are ready to move into get taken first. If your unit still smells during this window, you may miss several good tenants and have to wait for the next cycle, which could be months away.

Reputation: agents and platforms remember

An agent who takes clients to a smelly unit more than once will quietly move it down their list. Comments in condo-rental groups and online platforms spread quickly. A single phrase, "the room smells", can undo the effect of beautiful listing photos.

Relationships and contracts: a tenant who moves in may want out

If a tenant does move in despite the smell and later develops headaches, or their child's allergies flare up, disputes over the deposit and early termination may follow. Tenancies that start badly rarely end well, and they eat far more of the owner's time than expected.

Family: one day you may live there yourself

Some owners plan for their children or parents to move in later. Leaving chemicals and mold in the unit without proper treatment is therefore not just a business issue; it can become a health issue for the people you care about most.

Why the usual quick fixes fail in a post-flood condo

1. Opening the window for a few days

Ventilation is good and necessary, but most condo units have windows on one side only, so air does not flow through. During the rainy season the outdoor air is very humid, and leaving the window open can push moisture back into walls that are not fully dry. Ground-floor units also have obvious security limits on leaving windows open when nobody is home.

2. Air fresheners, reed diffusers and scented candles

These products work by masking odour, not by destroying its source, and their fragrances are themselves another group of VOCs. Spraying before a viewing simply layers a new smell over the old one. Viewers with sensitive noses usually notice that something is being hidden.

3. Charcoal bags, coffee grounds and baking soda

Absorbent materials have limited surface area and saturate quickly when faced with the volume of emissions from a whole-room renovation. They can help in a small cupboard, but they cannot reach compounds embedded in wood, walls and flooring across the unit.

4. Ordinary air purifiers

Purifiers built around HEPA filters are designed to trap dust and particles. VOCs are gas molecules, far smaller than particles. Without a substantial activated-carbon stage a purifier does little for chemical odour, and even with carbon, the filter needs frequent replacement in a freshly renovated room.

5. Painting over mold and water stains

Painting over dark stains or tide marks without removing soaked material and waiting for real dryness just hides the problem. Mold inside the wall keeps growing, mustiness keeps seeping out, and the new paint adds another layer of VOCs, creating a blended smell that is harder to treat than before.

6. Closing up the room with the air conditioner on

Some owners leave the air conditioner running so the room feels cool for viewings. But most condo units recirculate indoor air rather than drawing in fresh air. Chemicals circulate inside, may settle on the coil and in the ducting, and get blown back out as odour every time the unit is switched on.

The answer: ozone chemical-residue and odour removal by World Health Disinfection

World Health Disinfection (WHD) provides an ozone chemical-residue and odour removal service for homes, condos, offices, factories, construction sites, hotels, storage facilities and vehicles. According to the service information, ozone (O3) breaks down odour molecules at the source instead of masking them like perfumes or sprays. It targets paint, thinner, epoxy and lacquer odours, VOCs and musty smells, and also helps deal with bacteria, viruses and mold. Afterwards, ozone reverts to oxygen and leaves no residue.

Why ozone suits a freshly renovated condo

Ozone is a gas, so it spreads through the whole room: behind cabinets, under the bed, inside wardrobes left open, under the sink, and onto surfaces that cloths and sprays cannot reach. This matters in units with several built-in furniture pieces, because the odour from engineered wood often concentrates inside the cabinets rather than on the outside.

Just as important, according to the service information WHD measures TVOC (total volatile organic compounds) with calibrated instruments before and after treatment. Owners are not left relying on a "feeling" that the smell has gone; they get numbers to compare, which also become evidence they can share confidently with agents and tenants.

How the service works

1. Consultation and site assessment. The team asks about room size, renovation work, materials used and flood history to plan machine placement and timing.
2. Baseline TVOC measurement. Calibrated instruments record the starting level.
3. Preparing the space. The room must be empty of people, pets and plants. Windows and doors are closed to create a sealed space; cabinet doors, drawers and under-sink cupboards are opened so the gas can reach inside.
4. Ozone treatment with a Master Ozone Generator. Concentration and duration are matched to the room's size and condition.
5. Rest and ventilation. The ozone is allowed to revert to oxygen and the room is ventilated according to procedure. Nobody enters during this time.
6. Post-treatment TVOC measurement. Results are compared with the baseline and summarised for the owner.
7. Handover. According to the service information, the space is ready to use about 2 hours after treatment.

Safety note: ozone treatment is carried out only in an empty, closed space. People, pets and plants must stay out until the rest and ventilation period is over, because ozone at treatment concentrations irritates the respiratory system. Ozone is a step that comes after mud removal, washing and drying. It does not replace removing soaked materials, physical cleaning, or medical care.

10 reasons to ozone-treat your condo before renting it out after the flood

1. It tackles odour at the source instead of masking it. Ozone breaks down paint, thinner and adhesive odour molecules rather than adding fragrance on top. See the ozone chemical odour removal service.
2. It reaches inside built-in furniture and dead corners. The gas spreads into open wardrobes, kitchen cabinets and the space under the bed.
3. It helps reduce lingering damp mustiness, especially in ground-floor units where water stood.
4. It helps deal with bacteria, viruses and mold on surfaces and in the air, according to the service information, as an extra layer after physical cleaning.
5. It leaves no residue. Ozone reverts to oxygen, so there is no chemical film on your new furniture.
6. You get before-and-after TVOC numbers to show agents and tenants.
7. The room is ready quickly, about 2 hours after treatment, so you can schedule viewings sooner. Learn more on the ozone service page.
8. It improves your chances with families and pet owners, the tenants most sensitive to chemical smells.
9. It lowers the risk of disputes after move-in. When a room is clean both to the eye and to the nose, the tenancy starts on the right foot.
10. Professional equipment and clear safety procedures. WHD uses a Master Ozone Generator and a defined process. Ask WHD for details.

Before and after ozone: same room, different first impression

Note: results depend on the room, the materials and any remaining moisture. If walls or floors are still damp, dry them first.

Example case: a ground-floor studio in eastern Bangkok

Example case (a simulated scenario to explain the process, not a real customer testimonial)

Fon owns a ground-floor studio in a small condo in eastern Bangkok. After the water receded she spent about two weeks removing the laminate floor, cutting out the lower gypsum, repainting, installing new kitchen cabinets and replacing a swollen bathroom door. In the third week she ran fans and a dehumidifier until the walls were properly dry, but the room still smelled too strong to show anyone.

She contacted the WHD team. They asked about the materials, advised her to remove personal belongings, potted plants and food, and to open every cabinet door. They took a baseline TVOC reading, set up the Master Ozone Generator, closed the room and waited until the rest and ventilation period was complete, then measured TVOC again for comparison. Fon sent the before-and-after results to her agent to use when presenting the unit.

What Fon remembered afterwards was not any single number but the feeling of opening the door the next morning: "the first time since the repairs that I didn't rush to open the window." She also chose a low-VOC paint for the final bathroom touch-up and scheduled viewings only after every job was finished, so no new smell would be added.

Recovery checklist: what to do before and after ozone

Phase 1: as soon as you can get in

• Check electrical safety before switching anything on; coordinate with the building's juristic office and an electrician. Never touch plugs or switches while wet.
• Wear rubber gloves, boots and a mask while removing mud and wet items.
• Photograph all damage for insurance claims and records.
• Remove soaked, hard-to-dry materials: mattresses, carpets, swollen ceiling boards and lower gypsum.

Phase 2: wash, disinfect and dry

• Wash mud off floors, walls and grout with clean water and detergent.
• Disinfect cleaned surfaces with a suitable disinfectant such as Chemgene HLD4H, following the label dilution and contact time.
• Run fans and dehumidifiers until materials are truly dry. Do not paint over damp walls.
• Wash air-conditioner filters and have a technician check units if water reached the outdoor unit or piping.

Phase 3: renovate smartly

• Choose paints labelled low-VOC and engineered wood with low formaldehyde emission ratings where possible.
• Finish all smell-heavy work, such as painting, glue-down flooring and silicone sealing, before ozone treatment.
• Allow paint and adhesive to cure according to the manufacturer's guidance.

Phase 4: ozone treatment and afterwards

• Before: remove people, pets, plants and food; open all cabinets and drawers; close windows and doors.
• During treatment and rest: nobody enters. Wait for the team to confirm it is safe.
• After: ventilate as advised and ask for the before-and-after TVOC readings for your records.
• Avoid air fresheners and scented candles before viewings; let the room smell naturally clean.
• If you add more paint or furniture later, assess whether another treatment is needed.

Frequently asked questions

When in the renovation should I book ozone treatment?

The best time is after all smell-producing work is finished (painting, flooring, cabinet installation and sealing) and after the walls and floor are fully dry, but before you invite tenants to view. That way the room is at its best on viewing day.

How long do I have to stay out of the room?

No people, pets or plants may be inside during treatment, the rest period and ventilation. According to the service information, the space is ready about 2 hours after treatment. The team will tell you when it is safe to go back in.

Will ozone damage my new furniture?

A professional treatment controls concentration and time for the space. If you have valuables or materials you are worried about, such as artwork, musical instruments or collectibles, tell the team in advance so they can be removed first.

Will one treatment remove the smell permanently?

Ozone deals with odour molecules in the air and on surfaces during treatment. If there is still a new source, such as a wall that is wet inside or fresh paint added afterwards, odour can return. Fix moisture first and plan the work in the right order. Before-and-after TVOC measurements show you how effective the treatment was.

Can it replace post-flood cleaning or disinfection?

No. Ozone is an additional step after mud removal, washing, surface disinfection and drying. Mud and dirt must always be physically removed first.

Do I need permission from the building management?

Inform the juristic office according to your building's rules about team access, equipment and timing, so neighbours know and nobody enters the unit by accident during treatment.

My new tenant has a baby or pets. What else should I do?

Allow enough ventilation time after renovation, choose low-VOC materials, have the unit ozone-treated properly and share the TVOC readings with the tenant. Numbers build far more trust than simply saying "the smell is gone".

Don't let chemical odour keep the unit you just rebuilt from being rented

Talk to WHD about ozone treatment for paint, new-furniture and musty odours in your post-flood condo, with TVOC measured before and after.

Get an Ozone Odour Removal Quote

Phone 065-556-6294 · LINE @whd268 · Email worldhealthdisinfection@gmail.com

Related services

• Ozone chemical-residue and odour removal
• Residential and building ozone disinfection
• Chemgene HLD4H medical-grade disinfectant

References

• 2026 Bangkok floods – Wikipedia
• Al Jazeera: Disaster zone declared across Bangkok
• CDC – Floods and cleanup
• WHO fact sheets