A Story from the Field: The Smell That Rises Through the Floorboards Every Evening

Auntie Boonruean is sixty-eight years old and lives in a traditional raised teak house on the bank of the Lopburi River in Maharat district, Phra Nakhon Si Ayutthaya. The house was handed down from her parents. Upstairs is the living space, built from old teak planks that have darkened over the decades. Downstairs, in the open space beneath the house that Thai people call the tai thun, the family used to keep a bamboo daybed, a hammock, rice-farming tools, fishing nets and a few sacks of odds and ends.

During the floods of 2026, the river rose until water filled the space under the house almost to the floor beams, and it stayed there for several weeks. Auntie Boonruean and her young granddaughter carried everything they could upstairs and waited. When the water finally receded, the space under the house was covered in a layer of grey-black mud almost a hand-span thick. Water hyacinth, leaves and floating rubbish were tangled around every post.

Her grandson came back from Bangkok for a long weekend. Together they shovelled out a good part of the mud and hosed down the ground and the posts until the area looked fairly clean. They felt relieved. But that relief did not last. Every evening, as the air cooled, a smell like a blocked drain mixed with rotten eggs drifted up through the gaps between the floorboards. It was strongest in the bedroom directly above the old storage corner. Within a week Auntie Boonruean had given up sleeping in her own room and was laying a mattress out on the front veranda instead.

Then her seven-year-old granddaughter developed an itchy rash on her legs after playing barefoot under the house, and Auntie Boonruean herself began coughing every night. "We washed it. We sprinkled lime. We burned incense to chase the smell away," she said. "Nothing works. It is as if the smell lives inside the wood."

Her experience is not unusual. Hundreds of riverside wooden homes across Maharat, Ban Phraek, Bang Ban and neighbouring districts of Ayutthaya are facing exactly the same problem after the water has gone. This article explains where the underfloor smell really comes from, why the common fixes so often fail, and how professional disinfection fogging combined with ozone treatment can help families move back into their homes with confidence.

Where Does the Rotten Mud Smell Under the House Come From?

It is tempting to think the smell is simply "the mud". In reality, the odor that rises from under a raised house after a flood is the combined result of several processes happening at the same time in a space that is damp, shaded, poorly ventilated and rarely cleaned. Understanding each source matters, because each one needs a slightly different response.

• Decomposing organic matter in the mud. Floodwater carries plant debris, dead insects and small animals, animal droppings and, very often, wastewater from drains and septic tanks. All of this settles into the mud layer. Once the mud is compacted and starved of oxygen, anaerobic microbes break the organic matter down and release sulfur-containing gases. That is the classic rotten-egg, sewer-like smell that so many families describe.
• Waterlogged timber. Wooden posts, floor beams, joists and the underside of floor planks that sat in dirty water for days or weeks absorb that water deep into the grain. As the wood slowly dries, the trapped water evaporates and carries odor molecules with it. This is why the smell can linger for many weeks even after the visible mud has been removed.
• Mold and bacteria on wooden surfaces. While the wood stays damp and the air underneath stays still, mold begins to grow as a white, green or black fuzz on posts, beams and the underside of the floor. Mold produces its own musty smell and releases spores into the air.
• Floorboard gaps acting like a chimney. Traditional teak floors have small gaps between planks. In the evening, warmer air from under the house rises naturally through those gaps into the bedrooms above, carrying odor and spores with it. That is exactly why so many families notice the smell most strongly at dusk and during the night.
• Items stored under the house. Sacks, nets, mats, old mattresses, cardboard boxes and farm tools that were submerged hold moisture and odor for a long time. Even a single soaked sack left in a corner can keep a whole area smelling foul.

Because the odor comes from soil, timber, air and belongings all at once, a fix that targets only one of them will almost always disappoint. A proper solution has to remove the source material, treat the surfaces, and deal with odor molecules and spores in the air.

More Than a Nuisance: The Real Impact on Health, Home and Family

Health. Mud left behind by floodwater can be contaminated with germs from sewage and waste. People who walk barefoot under the house, or who have cuts and scratches on their feet and legs, face a higher risk of skin infections. Leptospirosis, the disease Thai people call "rat urine fever", spreads through water and soil contaminated with the urine of infected rats, and it is a well-known risk after floods in central Thailand. Diarrheal illness is another concern when contaminated mud is tracked indoors or touches kitchen areas. Meanwhile, mold spores carried upward with the smell can trigger allergies, a blocked or runny nose, sneezing and coughing, and can worsen asthma. Small children who love to play under the house, and older family members who sleep upstairs directly above the damp space, deserve extra protection. Anyone with unusual or persistent symptoms should see a doctor or visit a local health centre.

The structure of the house. Wood that stays wet for long periods begins to rot. Damp timber attracts termites and other insects, while nails, bolts and metal brackets start to rust. If the problem is left for months, structural repairs can end up costing far more than addressing the damp and contamination early.

Time and family life. Many children and grandchildren who work in Bangkok or other provinces want to bring their parents home as quickly as possible. A persistent smell, and the worry about germs, forces them to delay. Some families take turns using their leave to come back and scrub the house again and again without seeing results, which is exhausting and frustrating for everyone.

Income. In many riverside communities the space under the house is not just storage. It is where people sell snacks, make traditional sweets, mend nets, run a small grocery counter or look after neighbours' children. As long as the smell lingers, that small but important source of income cannot restart.

Why the Usual Fixes Don't Work

Families in Maharat are resourceful, and most have already tried several things before they call for help. Here is why those common methods tend to fall short:

• Hosing down with water only. Water pushes surface mud away, which is a good first step. But without disinfection, the extra moisture actually speeds up the growth of mold and bacteria on posts and beams. Many families find the smell gets worse a few days after a thorough wash.
• Pouring on strong bleach. Diluted bleach has a role on hard, non-porous surfaces that have already been cleaned of mud. Poured onto ground or wood that still carries mud, its effectiveness drops sharply because organic matter neutralizes it. In a confined, poorly ventilated space under a house, chlorine fumes can also irritate the eyes and airways. Bleach must never be mixed with toilet cleaners or ammonia-based products.
• Sprinkling lime or odor powder. Agricultural lime can help condition the soil surface a little, but it does nothing for the timber, the beams or the underside of the floor planks, which are a major source of the smell.
• Incense and air-freshener sprays. These only mask the odor. When the fragrance fades, the original smell returns, and the family is left breathing extra volatile compounds on top of everything else.
• Painting or oiling over the wood. If the timber is still damp and carrying mold, a fresh coat of paint or oil seals the moisture in. Mold often reappears under the coating within a few weeks, and the surface then has to be stripped.
• Fans blowing under the house. Fans do help timber dry faster, which is useful. But they also stir up mold spores and push them upward through the floorboard gaps into the rooms above.

The core problem is that the underfloor smell has several layers. Fixing only one layer is not enough. What is needed is a process that combines removing the remaining mud, disinfecting every exposed surface, and breaking down odor molecules and airborne spores.

The Solution: Chemgene HLD4H Disinfection Fogging Plus Ozone Treatment from World Health Disinfection

The World Health Disinfection (WHD) team uses two complementary techniques that work together to tackle the underfloor smell at its source.

1. Disinfection fogging service with CHEMGENE HLD4H. The disinfectant is applied as an ultra-low-volume (ULV) fine mist. Because the droplets are so small, they drift into the gaps around posts, the space between beams and joists, the joints between floor planks and the shaded corners that a cloth or brush simply cannot reach. This helps reduce bacteria, viruses and mold on surfaces that were in contact with floodwater.

2. Ozone treatment service. Ozone is a gas that spreads throughout an enclosed space. It reacts with odor-causing molecules through oxidation, breaking them down rather than covering them up, and it helps deal with mold spores floating in the air. For raised houses, the team treats the upstairs rooms that can be closed, and assesses whether part of the underfloor area can be temporarily enclosed with tarpaulins so the ozone can work effectively. Open areas that cannot be enclosed are handled mainly with disinfection fogging, mud removal and moisture control instead.

Step-by-Step Service Process for Raised and Stilt Houses

1. Site survey. The team checks the flood line on the posts, the depth of the remaining mud, the condition of the timber and beams, and which rooms upstairs are affected by the smell. Photos are taken for later comparison.
2. Mud removal and clearing advice. The team advises the family to shovel out the remaining mud and to move sacks, mats, mattresses and soaked items out from under the house. Items that should be thrown away are separated from those that can be washed and reused. Anyone doing this work should wear rubber boots, rubber gloves and a mask.
3. Disinfection fogging. Chemgene HLD4H is applied as a fine mist over posts, beams, joists, the underside of the floor, the staircase and any upstairs walls that were affected by damp.
4. Ozone shock treatment. Upstairs rooms and any enclosed sections are sealed, and the ozone generator runs for a duration based on the size of the space and the intensity of the smell. During this time, there must be no people, pets or plants inside.
5. Ventilation. Doors and windows are opened so fresh air can flow through for the full period the team specifies before the family re-enters.
6. Re-check and aftercare advice. The team assesses the odor after treatment, gives advice on managing moisture under the house, and schedules a follow-up check if the timber is still very wet.

10 Reasons Stilt-House Owners in Maharat Choose Disinfection and Ozone Treatment

1. It tackles odor at the source, on the timber and in the air, instead of hiding it, through our ozone treatment service.
2. The fine mist reaches gaps around posts, beams and floorboard joints that hands and brushes cannot, through our disinfection fogging service.
3. It uses CHEMGENE HLD4H, a disinfectant designed for surface disinfection.
4. It helps reduce the mold spores rising into the upstairs bedrooms where elders and children spend the most time.
5. You do not have to wait months for the wood to dry completely and hope the smell fades on its own.
6. There is a clear safety procedure, with leave and return times explained in advance.
7. You get practical advice on mud removal, what to throw away and how to reduce moisture from a team that works on flood-affected homes every day.
8. It reduces the burden on adult children who would otherwise take repeated leave to come home and scrub again.
9. It can be combined with our dust mite removal service for upstairs mattresses and pillows, and our mosquito spraying service for the area around riverside homes.
10. Booking is easy by phone or LINE, with site surveys available in Maharat, Ban Phraek, Bang Ban and nearby districts.

What Homeowners Can Do Themselves, Before and After the Service

Professional treatment works best when the family has prepared the space and keeps up good habits afterwards. Here are practical steps that make a real difference:

• Remove as much mud as possible. Leftover mud is the main source of the smell. Shovel it out down to the original soil level and pile it well away from the house, ideally where it can dry in the sun.
• Open up airflow. If the space under the house is partly enclosed with corrugated metal sheets or wooden slats, open some sections during the day so that wind can pass through and help the soil and posts dry faster.
• Lift belongings off the ground. Anything you plan to keep under the house should sit on shelves or raised platforms, not directly on damp soil.
• Inspect the timber regularly. Look for mold patches, soft spots and termite trails at the base of posts and along beams. Take photos every week so you can compare changes over time.
• Wipe high-touch surfaces. Stair rails, door handles and tables are touched many times a day. The Chemgene HLD4H 750 ml disinfectant spray is convenient for daily upkeep between professional treatments.
• Wash hands after every session under the house. If you have any cut or scratch on your feet or legs, cover it securely with a waterproof dressing before working in mud.
• Watch the weather. If rain returns, check whether water pools under the house again. Standing water will restart the cycle of odor and mold, so improving drainage around the posts is worth discussing with a local builder.

Before and After Disinfection and Ozone Treatment

Customer Voice (Example Scenario)

"The team went right under the house and shone a torch on every post. They told us the smell was coming from waterlogged wood and the mud still left in the corner. They had my grandson clear that out first, then they sprayed and ran the ozone. Now I can sleep in my own room again. The smell is much lighter."

— Auntie Boonruean, raised wooden house, Maharat district (example scenario)

Frequently Asked Questions

Q: The space under my house is open on all sides. Can ozone still be used?
A: Ozone works best in enclosed spaces. The team focuses ozone treatment on upstairs rooms and any sections that can be temporarily enclosed. Open underfloor areas are handled mainly with disinfection fogging, mud removal and moisture control.

Q: Do I have to wait for the wood to dry completely before calling for service?
A: No. You do not need to wait for the timber to be fully dry, but you should remove as much mud as possible first. Disinfecting early helps slow the spread of mold.

Q: We keep chickens and a dog under the house. Where should they go during treatment?
A: All animals must be moved out of the treated area during ozone treatment and throughout the ventilation period. The team will tell you the exact times in advance.

Q: Will the smell be gone for good?
A: If the root causes, such as leftover mud and trapped moisture, are dealt with, the smell will drop dramatically. If the timber is still very waterlogged, a follow-up check and a second treatment may be recommended.

Q: Is the disinfectant safe on old teak?
A: The team assesses surfaces before fogging and uses an amount suited to the material. If you have carved woodwork or valuable antiques, please let the team know before work begins.

Q: Is this medical advice for the rash and cough in my family?
A: No. This article is general information about cleaning and disinfecting homes. For any health symptoms, please consult a doctor or your local health centre.

Q: Which areas of Ayutthaya do you cover?
A: Maharat, Ban Phraek, Bang Ban, Bang Pahan, Phra Nakhon Si Ayutthaya and neighbouring districts. Contact us on LINE @whd268 to check availability.

Let Your Riverside Home Breathe Again

Book a site survey for your raised house in Maharat or nearby districts today.

Book Ozone Treatment – Click Here

See Disinfection Service – Click Here

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

Related Links

• Residential ozone disinfection
• Ozone treatment for odors and chemical residue
• Master Ozone Generator
• All articles

Health reference: World Health Organization (WHO): Floods · Department of Disease Control, Thailand