A typical scenario (an illustrative story based on common situations, not a review from a specific customer)

A seventy-year-old teak house on the Yom River and a smell it never had before

Aunt Boonmee lives in a raised teak house beside the Yom River in Mueang Sukhothai. Her father built it before she was born: sixteen hardwood posts, hand-polished teak panel walls, and wide floorboards that creak softly underfoot, a sound her grandchildren have known all their lives. Most years the river reaches the open space beneath the house, the tai tun. Some years it does not. The family is used to carrying things upstairs when the water comes.

That year the water came faster and higher than ever. It filled the space under the house to the top of the posts and rose almost half a meter over the upper floor, where it stayed for nearly three weeks. Aunt Boonmee went to stay with her daughter in town. When she returned, the underfloor space was covered in mud almost a hand-span deep. Two antique cabinets that could not be lifted in time had swollen so much their doors would not close. The lower wall panels carried a sharp water line, and some floorboards had cupped so badly that people tripped on them.

The family washed away the mud, scrubbed the floors, opened every window and assumed that such an airy wooden house would dry by itself within days. A month later, a damp, musty smell rose from the floor every morning. Thin white fuzz appeared in the gaps between boards and behind the cabinets. In the corner of the bedroom where Aunt Boonmee sleeps, tiny black dots spread along the joints, and she began coughing more at night. Her grandson, who has allergies, came to visit and sneezed all night, and ended up sleeping in a hotel.

This happens to many wooden homes in flood-prone provinces, from Ayutthaya, Ang Thong and Sing Buri to Sukhothai, Phitsanulok and Ubon Ratchathani. Wood behaves almost like a living material: it absorbs water, releases it slowly, and serves directly as food for fungi. Recovering a wooden house after a flood is very different from recovering a concrete one, and it requires more than washing and waiting.

Why wooden houses and traditional Thai homes suffer more mold after floods than concrete ones

Wood is made of cellulose and lignin, which are excellent food for many fungi. When wood is dry, its moisture content is too low for mold to grow easily. But when timber soaks for days or weeks, water penetrates deep into it, especially at end grain, joints, nail holes and cracks. The surface may dry in a few days, while the core stays damp for weeks or even months, depending on thickness, weather and airflow.

Surface mold: white fuzz, black dots and green stains

Most mold you see on wood after a flood is surface mold feeding on dirt, silt and sugars on the surface. It appears as white fuzz, black dots or grey-green stains. These molds do not rot wood immediately, but they release huge numbers of spores into the air and are the main cause of musty odors. In a wooden house full of gaps, spores lodge in grooves, joints and the back of panels that hands cannot reach.

Wood-decay fungi: the long-term threat to structure

Another group of fungi eats the wood itself, which carpenters call rot. Some types turn wood dark brown and make it crack into cubes that crumble when dry. Others bleach it pale, soft and stringy. Decay fungi need consistently high moisture in the wood, so they usually start at post bases touching damp ground, beams under poorly ventilated floors, and spots where water collects repeatedly. Ozone does not repair rotten timber. Wood that has lost its strength must be assessed and replaced by a carpenter.

The underfloor space: where mud and moisture stay longest

The open space under a raised house is the lowest point, the first to flood and the last to drain. Afterwards it holds mud, floating debris, small dead animals and puddles, which breed bacteria from sewage and animal urine, including the leptospirosis bacteria behind "rat urine fever," as well as mosquitoes. Moisture from below evaporates constantly into the floorboards above. That is why the upper floor dries so slowly, and why musty air seems to rise from the floor on cool mornings.

Panel walls and the gaps between boards

Traditional frame-and-panel walls and overlapping board walls have frames and cavities inside. Water that seeps in sits in tongue-and-groove joints and panel frames. The outside looks dry while the inside stays damp and dark, exactly what mold likes best. Many houses have extensions built with plywood or composite board, which swell, delaminate and grow mold much faster than solid wood and usually need to be removed.

Termites and other insects that follow

Damp wood attracts subterranean termites far more than dry wood. After a flood, termites often move their colonies upward along posts and walls, so a wooden house that stays damp is at higher risk in the following months. Termites need specialist pest control; ozone does not replace that. Drying the wood quickly, however, reduces the chance of an infestation.

Symptoms to watch, and who is most at risk

Breathing mold spores for long periods can cause congestion, sneezing, runny nose, itchy eyes, chronic cough, chest tightness and asthma flare-ups. Some people get itchy skin rashes. Those most at risk in a wooden house are:

• Older people, who are often the main residents of old family houses, spend all day at home and may have lung or heart disease.
• Young children, who crawl and sit on the floorboards, close to the moisture and spores rising from below.
• Pregnant women, who should avoid long exposure to mold and dried mud dust.
• People with chronic illness, including diabetes, cancer patients, people on immune-suppressing medicine, and those with allergies, asthma or COPD.

Anyone who waded through floodwater or shoveled mud under the house and then develops a high fever, severe calf pain, red eyes, yellowing skin or diarrhea should see a doctor immediately and mention their flood exposure. People whose cough or asthma worsens after moving back in should also consult a doctor. Managing mold at home reduces exposure. It is not medical treatment.

The impact goes far beyond mold stains on wood

Health

Many wooden houses belong to elderly owners who will not move because they love their home. Sleeping with mold spores every night can gradually worsen coughs, allergies and chronic breathing problems until hospital visits become frequent.

Money

The old hardwood used in traditional Thai houses is now rare and very expensive. If moisture and mold are left until timber rots, replacing posts, beams or a set of panel walls can cost many times more than doing recovery properly from the start, not counting termite treatment that may follow.

Heritage and sentimental value

Traditional Thai houses and old wooden homes are worth far more than their price. They hold memories of several generations. They are where families make merit and gather at Songkran, and some attract visitors interested in architecture. Letting a house decline because of post-flood damp means losing something that cannot be bought back.

Family

When the house smells and an allergic grandchild cannot stay, the family gathers less and elders feel more isolated.

Why common fixes fail in wooden houses

1. "It is an airy house, it will dry on its own"

Wooden houses do breathe better than concrete ones. But in the rainy season, when humidity stays high almost all day, thick waterlogged timber releases moisture very slowly. If mud and puddles remain under the house, the floor keeps receiving moisture from below. Waiting for it to dry naturally can take months, long enough for mold to establish itself fully.

2. Pouring bleach on wood

Bleach lightens surface stains, but it does not reach fungal threads inside the wood, and its water content adds more moisture. It can also blotch and fade teak or oiled wood, ruining a patina built up over decades.

3. Applying lacquer, polyurethane or paint straight away

Sealing wood while it is still damp inside traps moisture and mold. The wood cannot breathe out, the finish blisters and peels, and mold returns as dark stains under the film. Everything then has to be sanded off and redone.

4. Scrubbing only the mold you can see

Visible spots are only what has surfaced. The back of the panels, under the floorboards, inside tongue-and-groove joints and behind cabinets against the wall are where most mold hides. Cleaning the surface alone does not truly reduce spores in the house.

5. Burning incense, mosquito coils or spraying fragrance

Fragrance does not remove the cause, and smoke irritates the airways of elders and allergy sufferers.

6. Ignoring mud under the house because "it is not inside"

The underfloor space is the root of the whole problem. As long as mud and standing water remain, damp and odor rise into the living floor, and no amount of cleaning upstairs will finish the job.

WHD ozone disinfection for wooden houses and traditional Thai homes

The Residential and Building Ozone Disinfection service from World Health Disinfection (WHD) uses ozone gas (O₃), which has strong oxidizing power. Released in a closed space, it behaves as a gas and slips into board gaps, joints, the back of cabinets, under beds and corners that cloths and brushes cannot reach. Ozone breaks down the cell structures of viruses, bacteria and mold and breaks apart musty odor molecules, then reverts to oxygen (O₂) without leaving chemical residue on the wood. That matters for old timber that should not be exposed to harsh chemicals.

According to the test results certified for the company by Thailand's Department of Medical Sciences and Intertek (UK), the WHD system eliminates viruses, bacteria and mold by 99.99%. Details are on the certification page.

What you need to know about wooden houses: ozone comes after mud removal, cleaning and reasonable drying of the wood. It does not replace drying, does not repair rot and does not eliminate termites. Wooden houses also have many air gaps, open underfloor spaces and slatted walls, so the team must assess which rooms can be closed, which need temporary sealing with plastic sheeting and tape, and which areas are too open to treat effectively, such as an underfloor space without walls. Those areas should instead be cleared of mud, washed and left to dry naturally.

Safety: ozone treatment must take place in a closed space with no people, pets or plants inside. Elderly residents must stay elsewhere during treatment and return only after the rest and ventilation period set by the team. For houses close to neighbors, or with spirit houses and altars, the team helps plan appropriately.

How the WHD team works on wooden houses

1. Survey. The team checks the flood line, feels for moisture in floors, walls and posts, finds the strongest odor sources, and flags spots where a carpenter should check strength or replace timber.
2. Zone planning. Rooms to treat are chosen, such as bedrooms, the main hall and storerooms, and large gaps in walls or louvered windows are temporarily sealed.
3. Preparation. Food, plants and pets are removed. Cabinets, drawers and wooden chests are opened so ozone can reach inside, and the team confirms nobody remains in the house.
4. Ozone release and contact time. About 30 minutes per zone, depending on room size and odor level.
5. Rest and ventilation. Ozone reverts to oxygen, windows are opened, and the team checks before inviting the family back in.
6. Aftercare advice. Guidance on underfloor ventilation, wood care, termite checks and early signs that mold may be returning.

Ozone jobs of 15,000 baht or more include a free medical-grade disinfectant spray. Homes that need additional surface care can also look at WHD's other disinfection services.

10 reasons to finish wooden house flood recovery with ozone

1. Ozone is a gas, so it penetrates board gaps and panel joints where brushes and cloths cannot go.
2. No chemical residue on old wood. It will not blotch teak or oiled finishes the way bleach can. Read more about the ozone disinfection service.
3. Fewer mold spores in bedroom air that older residents breathe all night.
4. It removes musty odor at the source instead of masking it with incense or sprays that irritate the lungs.
5. It treats antique cabinets, chests and furniture worth keeping, reducing the musty smell inside them together with the room.
6. Short time away. About 30 minutes per zone plus rest and ventilation, so elderly residents can spend half a day at a relative's house and come home.
7. Assessment tailored to real wooden houses. The team knows which rooms can be closed, which need temporary sealing, and says honestly which parts a carpenter should see first.
8. Certified testing by the Department of Medical Sciences and Intertek (UK), according to the test results certified for the company.
9. Grandchildren with allergies can stay over again, and the family can gather at the old house once more. See the residential ozone service.
10. A careful way to care for family heritage, alongside drying, repairs and termite prevention. Ask us via Contact us.

Before and after: a wooden house restored step by step

Example case: a cluster of Thai houses in Ayutthaya used for merit-making every year

Example case (an illustrative scenario to explain the process, not a real customer review)

Somsri looks after her family's cluster of three traditional Thai houses in Bang Pa-in, Ayutthaya, where the family holds its annual merit-making and Songkran reunion. In a severe flood year, water covered the main bedroom to about thirty centimeters and the underfloor space stayed submerged for over two weeks.

After the water receded, relatives helped wash out the mud and scrub the floors. Two months later, while preparing for the ceremony, the main house still smelled strongly musty. Wooden chests storing old silk and heirlooms smelled stale inside, and white mold grew along the frames of the panel walls. Somsri was worried because several elderly relatives were over eighty.

The team's survey found mud still piled around the post bases and water sitting in hollows under the house, sending moisture upward constantly. The first recommendation was to clear all the mud underneath, regrade the ground so water would not pool, and have a carpenter check two post bases that looked unusually dark. Fans and dehumidifiers then ran in the main house for about two weeks, and surface mold on the panels was removed with soft brushes and damp cloths, without bleach.

Once the wood was clearly drier, ozone treatment was scheduled. Folding windows and vents above doors were temporarily sealed with plastic, every chest and cabinet was opened, and the work was divided into three zones, one per house. The family waited at a relative's house across the road until the rest and ventilation period was over.

On the day of the ceremony, the elders sat in the main house for the whole event and nobody mentioned the smell. The chests were used for storing fabric again. The carpenter found early rot in the post bases, so the family planned reinforcement, a reminder that ozone is one part of recovery, not all of it.

Recovery checklist for wooden houses and traditional Thai homes

Safety first

• Switch off power before entering. Old wooden houses often have wiring fixed to timber walls, so have an electrician check before use.
• Test cupped or soft floorboards before walking on them and watch for protruding nails.
• Wear boots, gloves and a mask while clearing mud underneath, and watch for snakes and other animals that sheltered from the water.
• See a doctor immediately for fever, calf pain or diarrhea after wading.

Clear mud and clean

• Remove all mud from under the house, drain standing water and level the ground so it does not pool.
• Wash floors and walls with clean water and mild detergent, then wipe until just damp. Do not flood the wood with water.
• Brush off surface mold along the grain with a soft brush while wearing a mask.
• Discard plywood, composite board, mattresses and fabrics that soaked in mud and smell strongly.

Dry the wood properly

• Open windows when the sun is out and use fans and dehumidifiers in rooms that can be closed. WHO and CDC advise starting cleaning and drying within 24 to 48 hours to limit mold.
• Pull furniture away from walls so air circulates behind it.
• If possible, use a wood moisture meter before re-oiling, sealing or painting.
• Avoid blasting wood with high heat, which can crack or warp it.

Check structure and termites

• Have a carpenter check post bases, beams and joists that soaked for long, especially soft or discolored spots.
• Watch for termite mud tubes on posts and walls in the following months and call a specialist if you find them.

Ozone day

• All people, pets and plants must leave the treated area. Elderly residents should stay elsewhere.
• Open internal cabinets, chests and drawers; close vents and windows as the team advises.
• Seal food and personal items you do not want exposed in closed containers.

After ozone

• Re-enter only when the team confirms the rest and ventilation period is complete.
• Keep the underfloor space and rooms ventilated and do not push items against wooden walls.
• If odor or mold returns, look for the moisture source: a leaking roof, water under the house or wood that is still damp.
• Oil or seal wood only once it is completely dry.

Frequently asked questions about wooden houses after floods and ozone

1. A wooden house has so many gaps. Can ozone really work?

Yes, in rooms that can be closed or temporarily sealed, such as bedrooms, the main hall and storerooms. The team assesses the house and seals large gaps with plastic first. Open areas such as an unwalled underfloor space are handled by clearing mud, washing and drying instead.

2. Can ozone fix rotten wood?

No. Ozone reduces mold and odor in the air and on surfaces, but wood that has lost its strength must be assessed and replaced by a carpenter. Ozone is a complement to recovery work.

3. How long should the wood dry before treatment?

It depends on timber thickness and weather. Generally, wait until surfaces are dry, no water seeps out and room humidity has dropped clearly. The team will assess this during the survey.

4. Will ozone damage old teak or antique furniture?

The team controls concentration and time to suit the space and will advise moving or storing especially delicate items, such as old silk, paintings or important collectibles, separately as a precaution.

5. What if a bedridden elder lives in the house?

The patient must always be moved out of the treated area. Treatment can be planned zone by zone, moving the patient to a part of the house whose air is genuinely separate, or to a relative's home for half a day. The team helps plan the safest option.

6. Price and promotions

Price depends on house size, number of zones and how difficult the space is to seal. Call or message on LINE for an assessment. Jobs of 15,000 baht or more include a free medical-grade disinfectant spray.

Let your family home smell of wood again, not mildew

The WHD team is ready to assess your wooden house or traditional Thai home after the flood and finish recovery with ozone treatment that leaves no chemical residue on the timber.

See the Ozone Disinfection Service

Call 065-556-6294  |  LINE @whd268  |  worldhealthdisinfection@gmail.com

Related pages

• Residential and Building Ozone Disinfection
• Ozone cleaning service
• Disinfection service
• Certification documents
• Contact us

References

• CDC: Floods (cleanup and mold guidance)
• Department of Disease Control, Thailand