Molds After Floods Ranked: 10 Types Found in Homes and Buildings in 2026, Where They Hide, How Harmful They Are, and How Disinfection Spraying Helps

Last updated: 6 Oct 2026 | 14 Views |

Molds After Floods Ranked: 10 Types Found in Homes and Buildings in 2026, Where They Hide, How Harmful They Are, and How Disinfection Spraying Helps

Within days of floodwater draining, many homes show black spots, green patches and white fuzz on the walls, along with a musty smell that will not go away. This is our ranking of molds after floods in homes and buildings: ten types commonly found in water-damaged structures, the materials each prefers, how they affect health, who should be most careful, and how to deal with them. We end with the post-flood disinfection spraying service from World Health Disinfection (WHD), a step that follows removing moldy materials, cleaning and drying, to help eliminate and prevent mold on surfaces.

The 2026 Floods and the Mold Problem That Follows

According to a Dailynews report citing the Department of Disaster Prevention and Mitigation (DDPM) at 06:00 on 5 October 2026, floods affected 26 provinces plus Bangkok, a total of 1,270,151 households. Homes, shophouses, schools and offices sat in water for days. Once the water dropped, the moisture trapped in walls, floors and furniture created exactly the conditions mold loves.

The US Centers for Disease Control and Prevention (CDC) advises cleaning and drying a home within 24 to 48 hours after floodwater recedes to limit mold growth. In practice, many families cannot get back in that quickly because roads are still flooded or the power is off, so mold has started before cleanup begins. The World Health Organization (WHO) indoor air quality guidelines on dampness and mould link living in damp, moldy buildings with respiratory symptoms and asthma.

How We Ranked Molds After Floods (Editorial, Not Official)

This is an editorial ranking by the WHD team, not an official ranking by any agency, and not based on detection counts from any survey. We considered:

How often the mold is described in water-damaged buildings in guidance from CDC, WHO and public health bodies, and in indoor mycology references.
Health effects, from allergy, asthma and irritation to infection in people with weak immunity.
Preferred materials and difficulty of removal; mold rooted in porous materials is harder to deal with than mold on smooth surfaces.
Growth speed and persistence, described qualitatively.
How well removal, cleaning, drying and disinfection prevent it.

One important point: you cannot identify mold species by eye, and color is not a reliable guide. The CDC says it is generally not necessary to identify the type before removal, because every type is handled the same way: remove it, clean, dry and control moisture.

Example Case: A Shophouse Where the Smell Survived Three Washes

(An example case, a typical scenario, not a real person.) May runs a small beauty salon on the ground floor of a riverside shophouse and lives upstairs with her primary-school daughter, who has asthma. The ground floor stood under about a metre of water for almost a week. Afterwards May scrubbed the tiles, wiped the salon chairs, opened the doors for airflow and repainted over the water marks so the shop would look new for reopening.

Two weeks later, clusters of black spots pushed through the fresh paint, green fuzz appeared behind the display cabinet, and the plywood partition swelled and smelled strongly musty. Some customers sneezed when they came in, and May's daughter began coughing at night until she needed to see a doctor. The problem was not that May cleaned too little. Moisture was still inside the walls and plywood, and painting over the mold simply hid it.

The 10 Molds After Floods, Ranked

The information below is general. Anyone with worsening asthma, breathing difficulty, a lasting cough or fever should see a doctor, especially people with weak immunity, lung disease, young children and older adults.

1Stachybotrys chartarum, the Black Mold on Gypsum and Wood

Why it ranks first: Stachybotrys is often mentioned in water-damaged buildings because it needs cellulose-rich materials that stay wet for a long time, exactly the condition of a flooded home. Often called black mold, it is greenish-black and can look slimy when wet. Its presence means the material has been wet long enough to be deeply damaged, which is why it tops our list as a warning sign.

Where it grows: the paper facing of gypsum board, the back of partition walls, plywood, cardboard, wallpaper and leaking ceilings.

Health effects: it may irritate the nose, throat and eyes and trigger respiratory symptoms in sensitive people. Long-term health effects are still studied, but the cleanup principles are the same as for other molds.

What to do: cut out or remove widely affected porous materials beyond the damp edge. Do not dry-sand, which spreads spores. Clean the remaining structure, dry it, then disinfect surfaces.

2Aspergillus, a Concern for People with Weak Immunity

Why it ranks second: Aspergillus lives in soil, dust and buildings and grows well on damp materials. Its tiny spores float easily. It rarely harms healthy people, but in those with very weak immunity, such as cancer patients on chemotherapy or organ transplant recipients, it can cause aspergillosis in the lungs, and some people with asthma react allergically to it.

Where it grows: dried mud and dust in corners, damp walls, ceiling insulation, air conditioners and wet piles of paper or books.

Health effects: allergy, asthma flare-ups and, in high-risk groups, infection that needs medical treatment.

What to do: people with weak immunity should stay out while moldy materials are removed and ask their doctor before returning. Cleaners should wear N95 masks, gloves and goggles. Disinfect after removal and drying.

3Penicillium, the Blue-Green Mold on Fabrics and Carpets

Why it ranks third: Penicillium is very common in damp homes and grows fast on fabric, carpets, mattresses, wallpaper and food. It is a major source of the closed-room musty smell and an important allergen. It rarely causes serious infection, but it is widespread and releases spores readily.

Where it grows: carpets, curtains, fabric sofas, mattresses, wardrobes, leather bags and food left in fridges during power cuts.

Health effects: sneezing, blocked or runny nose, itchy eyes and asthma flare-ups in allergic people.

What to do: hot-wash fabrics that can be laundered and dry them fully in the sun. Carpets and mattresses soaked by floodwater usually need to go. Clean cupboards and shelves, then disinfect.

4Cladosporium, Dark Spots on Painted Walls and Window Frames

Why it ranks fourth: Cladosporium is one of the most common molds indoors and outdoors and can grow on surfaces that are only humid, such as painted walls in damp rooms. It is a common allergen. It ranks fourth because it is so widespread, though its effects are mainly allergy and asthma.

Where it grows: painted walls, window frames, bathroom grout, curtains, wood and air-conditioner coils.

Health effects: nasal allergy, coughing, asthma flare-ups and, in some people, skin rashes.

What to do: wash smooth surfaces with detergent, service air conditioners, lower indoor humidity and disinfect surfaces.

5Alternaria, Linked to Asthma

Why it ranks fifth: Alternaria appears often in allergy research because of its link with asthma in sensitised people. It comes from soil and plants and settles in damp homes, especially where water collects repeatedly.

Where it grows: leaking window surrounds, showers, under sinks, indoor plant pots and damp carpets.

Health effects: asthma, wheezing, sneezing and a blocked nose, particularly in allergic children.

What to do: fix leaks, dry surfaces, move damp potted plants out of bedrooms, clean, then disinfect. Children with allergies should stay away during cleanup.

6Chaetomium, in Walls Wet for a Long Time

Why it ranks sixth: like Stachybotrys, Chaetomium favours cellulose materials that stay wet, and the two often appear together in long-flooded buildings. It is often linked with strong musty odours, a sign that materials inside are still damp.

Where it grows: gypsum, wallpaper, wood, laminate floors and cardboard on the floor.

Health effects: respiratory irritation and allergy in people sensitive to mold.

What to do: measure moisture in walls, remove deeply damp materials, let the structure dry, then disinfect before installing new materials.

7Mucor and Rhizopus, the Fast-Growing Fuzzy Molds

Why it ranks seventh: these molds grow very fast, showing as white-grey fuzz on food, plant debris and wet organic matter. The risk to most people is low, but in people with poorly controlled diabetes or very weak immunity they can, rarely, cause serious disease.

Where it grows: spoiled food, flooded kitchen produce and organic debris washed in by the water.

Health effects: allergy, and in high-risk people a possible infection that needs urgent medical care.

What to do: discard all food and organic waste that touched floodwater and clean the fridge and kitchen. People with diabetes should let others do this work. Then disinfect the kitchen.

8Trichoderma, Green Mold on Wood and Paper

Why it ranks eighth: Trichoderma lives in soil and on wet wood, often as bright green patches. It degrades wood and paper and can be an allergen. It ranks mid-table because material damage is more obvious than health effects.

Where it grows: door frames, wooden stairs, wooden furniture, documents, books and cardboard boxes.

Health effects: allergy and irritation in some people.

What to do: scrub and dry solid hardwood that is still sound; swollen plywood and moldy documents usually need to be discarded or sent to specialists. Disinfect remaining surfaces.

9Fusarium, Soil Mold Carried in with Mud

Why it ranks ninth: Fusarium lives in soil and plants and arrives with flood mud and plant debris. It can grow on water-damaged materials. It occasionally causes eye or nail infections and can be more serious in people with weak immunity, but this is uncommon.

Where it grows: mud not yet removed, damp areas near doors, plant pots and doormats.

Health effects: allergy and, uncommonly, local infections in vulnerable people.

What to do: remove all mud, wash floors, dry, then disinfect. Contact lens wearers should be careful with hand and eye hygiene.

10Aureobasidium pullulans, Black and Pink Stains on Grout and Windows

Why it ranks tenth: this mold grows on grout, silicone, window frames and painted surfaces in bathrooms that stay damp. It can be an allergen, but its overall severity is lower than the others here. It is still a sign that a room is too humid.

Where it grows: tile grout, silicone around tubs, aluminium window frames and bathroom walls.

Health effects: allergy in people sensitive to mold.

What to do: scrub, replace deeply stained silicone, run an exhaust fan and disinfect the bathroom after cleaning.

Who Should Be Most Careful About Molds After Floods

People with asthma or allergies, who should stay away while materials are torn out.
Young children, who breathe fast and spend time near the floor.
Older adults and people with chronic lung disease.
People with weak immunity, who should consult a doctor before returning.
People with poorly controlled diabetes, who should avoid handling organic waste and moldy materials.
Cleaners and staff, who need protective equipment.

How Molds After Floods Affect Homes, Shops and Buildings

Health: household members sneeze, cough and have asthma flare-ups more often. Some cannot sleep because of blocked noses, especially in bedrooms kept closed with the air conditioning running.

Property: mold feeds on materials, leaving gypsum crumbly, wood rotten and fabrics permanently stained. Furniture that could have been saved on day one may have to be thrown away if left too long.

Business: shops and offices with a musty smell put customers off, staff take more sick days and the image of cleanliness suffers.

Cost: painting over mold looks cheap, but when the mold pushes through again you pay twice, for tear-out and for repainting.

Why Bleach and Repainting Alone Fall Short

Painting over mold: the mold stays underneath and returns while moisture remains. CDC advises against painting or caulking over mold.
Bleach on porous materials: it may not reach mold rooted deep in gypsum or plywood; these usually need removal.
Mixing products: bleach with ammonia or other cleaners produces dangerous gases, a clear CDC warning.
Dry scrubbing spreads spores through the house.
Fans alone dry surfaces but also spread spores if the area has not been cleaned.
Air fresheners mask smells without fixing the cause.
Dead mold can still trigger allergies, so killing it is not enough; it has to be removed.

The correct order is remove, clean, dry, then disinfect, while keeping humidity under control. Disinfection spraying reduces what remains on surfaces once the source is gone.

WHD Post-Flood Disinfection Spraying: Eliminating and Preventing Mold on Surfaces

World Health Disinfection provides post-flood disinfection spraying by trained technicians using spraying and/or ULV (Ultra Low Volume) fogging so fine droplets reach walls, corners, the backs of cupboards and surfaces a cloth cannot. According to the service information, the disinfectant is CHEMGENE HLD4H, a medical-grade UK disinfectant containing Benzalkonium Chloride and Didecyldimethylammonium Chloride.

Product and service information state that it covers viruses, bacteria and fungi, with a claimed 99.99% efficacy, and describe it as broad-spectrum. The website lists approvals or references from the Department of Medical Sciences, Mahidol University, NHS England and EN 14476:2013+A2:2019. The individual molds on this list, such as Stachybotrys, Aspergillus or Penicillium, are not named on the website, so we say plainly that coverage is at the fungi-group level according to product information. If you need test data for a particular mold, ask the WHD team.

The Service Process

Survey: the team checks the extent of mold, damaged materials, remaining moisture and who uses the building, such as children with asthma, to plan zones.
Mud removal, tear-out and washing first: mud is cleared, heavily moldy porous materials removed, surfaces washed and dried. Spraying does not replace this step.
Zoning: everyone, including pets, leaves the spray zone; food and personal items are covered or removed.
Spraying: technicians spray or ULV-fog walls, floors, timber framing, cupboards, shelves, bathrooms and areas behind furniture.
Re-entry: according to the service information, wait about 30 minutes before normal use. Follow the time the technicians give and ventilate.

We do not claim the product leaves no residue; technicians advise on food-contact surfaces afterwards. According to the service information, the promotion includes a free CHEMGENE spray bottle and WELLGIENIC wet tissues, and a tax invoice is available. If a musty smell lingers after moisture is fixed, add the residential ozone disinfection service.

10 Reasons to Add Disinfection Spraying After Mold Cleanup

A finishing step after tear-out that reduces germs on remaining structures.
ULV droplets reach behind cupboards, under stairs and open ceiling frames.
Less need for strong bleach with harsh fumes.
Medical-grade disinfectant described as covering fungi, bacteria and viruses.
Trained technicians who know where mold tends to return.
Planning around occupants, such as a child's bedroom in an asthma household.
Suitable for shops and offices reopening with confidence; see the disinfection service page.
A clear re-entry time to plan reopening.
Ozone add-on for musty air.
Easy contact: call 065-556-6294 or LINE @whd268 to book a site survey.

Before and After Disinfection Spraying

Before spraying

Black spots and green patches on lower walls
A strong musty smell on entering
White fuzz on cupboards and shelves
Frequent sneezing and coughing
Doubt about whether mold will return

After spraying

Heavily moldy materials removed
Remaining surfaces cleaned and disinfected
An ongoing humidity-control plan
Less musty smell once moisture is fixed
Owners know how to monitor mold long term

Example Case: A Ground-Floor Accounting Office That Had to Reopen Within a Week

(An example case to explain the process, not a real customer review.) Oat owns a small accounting office on the ground floor of a three-storey commercial building. The floor was flooded for several days, and files, plywood partitions and carpet all grew mold. He needed to reopen in time for his clients' filing deadlines.

After the survey, the WHD team suggested sending salvageable important documents to a document recovery specialist, discarding the carpet and plywood partitions, cutting out the damp lower gypsum walls and running dehumidifiers for several days until the walls were dry. Only then did the team spray the whole ground floor, including the exposed wall framing, desks and the bathroom. Once the re-entry time had passed, the contractor installed new walls straight away, and staff returned with dehumidifiers still running.

Checklist Before and After Spraying

Before spraying

Wear an N95 mask, rubber gloves and goggles.
Keep people with asthma, children, older adults and immunocompromised people elsewhere.
Discard carpets, mattresses, upholstery and porous items soaked or heavily moldy.
Cut gypsum walls above the water line and beyond the damp edge.
Wash hard surfaces with water and detergent.
Ventilate and use fans and dehumidifiers until materials are dry.

After spraying

Re-enter at the time given and ventilate.
Keep humidity low with dehumidifiers.
Service air conditioners before use.
Check corners and behind furniture weekly in the first month.
Do not paint or wallpaper until walls are fully dry.
See a doctor for worsening asthma or a persistent cough.

FAQ: Molds After Floods and Disinfection Spraying

Do I need to identify the mold first?
Generally no, according to CDC. Every type is handled the same way. This ranking explains risk; it does not replace laboratory testing.

Can I spray without removing walls?
Not recommended. Heavily moldy porous materials should be removed first; spraying comes after removal, cleaning and drying.

Is black mold more dangerous than other colours?
Colour does not reliably show type or danger. Handle all indoor mold with the same principles.

Does CHEMGENE kill every kind of mold?
Product information says it covers fungi but does not name individual molds. Ask WHD for species-specific test data.

How long does a shop need to close?
It depends on the size of the area and the tear-out and repair work. For the spraying itself, the service information says to wait about 30 minutes afterwards, but always follow the time the technicians give on the day.

Will mold come back after spraying?
If humidity stays high or leaks continue, yes. Moisture control matters most long term.

Let WHD Finish Your Post-Flood Mold Cleanup

Having ranked the molds after floods, they all share one weakness: moisture. Let WHD plan with you from survey to disinfection spraying after tear-out and drying, to help eliminate and prevent mold on surfaces in your home, shop or building.

Book a Survey and Disinfection Spraying

Call 065-556-6294 · LINE @whd268

Related Services and References

#MoldsRanked #MoldAfterFlood #FloodGerms #DisinfectionService #PostFloodDisinfection #FloodCleanup #MoldRemoval #Chemgene

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