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Monsoon mould and damp walls: what cleaning can and cannot fix

From October to December walls sweat, wardrobes smell and black spots appear. Which a deep clean solves, which are a leak in disguise, and what to do meanwhile.

4 min read · Updated 19 August 2026

A deep clean will remove the mould you can see, the musty smell it causes, and the damp film on tiles, glass and furniture. It will not stop the mould coming back if the wall is still wet. In Nellore the monsoon runs October to December, humidity stays high most of the year, and on the coastal side the air is salty as well as wet, so the real question about any damp patch is: is this the weather, or is this a leak? Cleaning fixes the first. Only plumbing or waterproofing fixes the second.

Here is how to tell them apart and what to do about each.

Weather damp: what cleaning fixes

This is mould from humidity and still air. It looks like scattered black, grey or greenish spots, usually:

  • On the lower part of outer walls, in corners, and behind wardrobes and cots pushed against them
  • In bathroom grout and around the basin
  • On the ceiling above the shower
  • On leather shoes, belts and bags in a closed cupboard
  • On the rubber seal of the fridge and the washing machine door

A deep clean treats these directly: surfaces are wiped down with a mild bleach or anti-fungal solution, grout is scrubbed, wardrobes are emptied and wiped inside, the fridge seal is cleaned, and the room is aired and dried. Soft furnishings are vacuumed. The smell goes with the growth.

If the wall is dry to the touch and the spots are on the surface of the paint, this will hold — as long as you keep air moving afterwards.

Leak damp: what cleaning cannot fix

This looks different once you know what to look for:

  • A patch that is darker in the middle and spreads outward, often with a tide-mark edge
  • Paint that bubbles, flakes or feels soft
  • White powdery crystals on the plaster (salts brought out by water)
  • A patch directly under a bathroom, a balcony, or the overhead tank, or on the ceiling of a top floor
  • A patch that stays wet in the dry season

This is water coming through the wall — rain seeping through an outside crack or a terrace that was never waterproofed, a leaking pipe inside the wall, a bathroom upstairs with failed tile grout, or a tank overflow running down the outside. Cleaning brightens it for a week. Then it is back, because the water is still coming.

Get the source found first: a plumber for pipes and bathrooms, a waterproofing or painting contractor for terraces and outside walls. Clean after.

The Nellore monsoon routine

What keeps weather damp from turning into a problem between October and December:

  1. Move the air. Open windows for an hour whenever it is not actually raining. A ceiling fan on low in a closed room helps more than most people expect.
  2. Pull furniture off outer walls. Two inches of gap behind the wardrobe and the cot is enough for air to circulate.
  3. Run bathroom exhausts after every use and keep the door open the rest of the time.
  4. Empty the wardrobe of anything leather or rarely used and wipe shelves monthly. A few silica gel packets or a bowl of rice in the corner helps.
  5. Dry clothes on the balcony or under the fan, not in the bedroom. Drying indoors adds litres of water to the air.
  6. Wipe the fridge door seal fortnightly.
  7. Check the balcony drain and terrace outlets before the first heavy rain. A blocked outlet is how rain ends up in your ceiling.

What never to do

  • Do not paint over mould. It grows back through the new paint within a season.
  • Do not mix bleach with acid (toilet cleaner) or with ammonia. The fumes are dangerous. One product, rinsed off, then the other if you must.
  • Do not scrub distemper walls wet. They mark. A dry brush and then repainting is the answer there.
  • Do not run a heater or keep a room sealed to "dry it out" — the moisture has nowhere to go.

When to call someone

Book a deep clean when the house smells musty, the spots are surface-level and scattered, and you want everything reset in a day. Call a plumber or waterproofing contractor first when the patch is spreading, bubbling, directly under a wet area, or still there in March. Mould in a room where someone with breathing trouble sleeps is a reason to act on either, soon.

Questions people ask

Is the black growth on my bedroom wall dangerous?
It is mould, and it is worth removing rather than living with, especially in a room where someone sleeps. Small patches on a painted wall can be cleaned. Large or recurring patches mean the wall is staying wet, and the fix is stopping the water, not just cleaning the surface.
Why does mould come back a week after I clean it?
Because the wall is still damp. Surface cleaning removes the growth but not the moisture that feeds it. If the patch is on an outer wall, behind a wardrobe, or under a bathroom, the cause is usually rain seepage, a pipe leak, or no air movement. Fix that and the cleaning holds.
Can I use bleach on mould myself?
On tiles and washable paint, a diluted solution (a capful in a mug of water) brushed on, left ten minutes and rinsed is fine. Open the windows, wear gloves, and never mix it with any other cleaner. Do not use it on distemper or on bare plaster — it marks and does not reach into the wall anyway.

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