Mould and fungus
Why walls turn black and green in the monsoon, and what to do.
Every Bengaluru monsoon, walls that looked fine in the dry months start showing black spots and green patches. Mould is easy to see and easy to wipe, and the real question is what's keeping the wall wet enough to grow it.
Reviewed 21 September 2026 by PremiumWalls operations.
At a glance
Why does mould keep coming back on my walls every monsoon?
Mould grows where a wall stays damp and the air barely moves. Humid monsoon air, a hidden leak, seepage through an outer wall or a closed-up corner can all supply that. Cleaning removes what you can see but leaves the moisture, so it returns. Lasting results need the source of the damp found and fixed, then anti-fungal treatment and repainting.
Mould and Fungus on Walls in the Monsoon
What's actually growing on the wall
Mould and fungus are living growths that feed on the dust, paint film and organic traces on a wall, provided there's enough moisture. Black, green, grey and sometimes brownish patches are all common. They tend to start in corners, behind furniture, around windows and on outer walls that stay cool and shaded.
Why the monsoon brings it out
Long spells of humid air mean walls can't dry properly, and windows tend to stay shut against the rain. Moisture then lingers in the wall and in the room. Add a slow seep through an outer wall or a leak from a neighbouring bathroom, and a wall that copes in the dry months gives up in the wet.
Three causes worth checking
It's usually one or more of these.
- Moisture entering from outside, through cracks, a terrace or parapet, or a damp exterior wall.
- A hidden leak from a pipe, bathroom, kitchen or air-conditioner drain.
- Poor ventilation, so moisture from cooking, bathing and drying clothes has nowhere to go.
Cleaning versus treating the cause
Wiping off surface mould makes the wall look better and is sensible for hygiene. It doesn't touch the damp behind it, and growth usually starts again once the humidity does. Treating the cause means tracing the moisture and dealing with it, which is why we look at the wall's surroundings before recommending anything.
What anti-fungal treatment does and doesn't do
An anti-fungal treatment is applied to a cleaned surface to kill existing growth and discourage new growth on the wall. It doesn't stop water entering the wall. If the moisture is still there, treatment on its own can be overwhelmed, so it works as part of the repair and not as a substitute for one.
Keeping it from returning
After the repair, a bit of habit helps. Open windows when the weather allows, run exhaust fans in bathrooms and kitchens, keep furniture a little away from outer walls and don't dry wet clothes in closed rooms. Any new patch that shows up should be looked at early, before it spreads across a whole wall.
Mould and Fungus on Walls in the Monsoon — your questions.
Can I just repaint over the mould?
Painting over mould that hasn't been cleaned and treated usually fails, because the growth carries on underneath and shows through or lifts the paint. The wall needs cleaning, treating and drying first, and the cause of the damp dealt with.
Is black mould on walls dangerous?
Mould can irritate the airways and worsen breathing problems for some people, particularly children, older people and anyone with asthma or allergies. If someone at home is affected, take it seriously and get the cause fixed without delay.
Why is it worse on the outer walls?
Outer walls are cooler and meet rain and humid air directly, so they hold moisture longer than inner walls. Cracks or a failing exterior finish let more water in, which feeds growth on the inside face.
Should I treat it before or after the monsoon?
Inspecting can happen any time, and finding the source during the rains can be easier. Repairs and repainting need dry surfaces, so the main work usually waits for a dry spell. A free colour and wall inspection with a written itemised quotation is where we'd start.
Let us look at your walls first.
Tell us about the property and we will set up a free colour and wall inspection. You get a written, itemised quotation afterwards, with no obligation to go ahead.
- We call you back the same day to get a picture of the property and the surfaces.
- We agree a time and come out for the free inspection.
- You get the written scope and itemised quotation.
- Nothing starts until you approve it.