Black or grey-green spots have appeared in the corners of the bedroom, along the ceiling edge or low on a wall behind the bed. You wipe them off and they return. Before you buy a bottle of anti-fungal paint, work out what is feeding them. Mould needs moisture. The only question is whether that moisture is coming through the building (a leak) or out of the room's own air (condensation).

Leak or condensation: why it matters

Condensation is fixed by airflow and habits. A leak is fixed by repairing the point where water enters. Treat a leak like condensation and you will clean the same corner every monsoon while the wall stays wet behind the paint.

A ten-minute diagnostic

  1. Check the timing. Does it get worse a day or two after rain, even on mornings that feel dry? That points to a leak. If it is worst on cool mornings and clears slightly by afternoon, think condensation.
  2. Look at the shape. A leak tends to leave a stain with an edge or tide mark, often brown or yellow, with mould on top. Condensation is usually a scattering of small dark dots, mostly in corners and behind furniture.
  3. Find which wall it is. Mould on an outer wall or top-floor ceiling can be a leak from the wall or terrace. Mould on inner walls with no stain suggests condensation or poor airflow.
  4. Touch it. A cold, slightly clammy surface that dries through the day suggests condensation. A patch that stays damp, feels soft, or has bubbling or flaking paint suggests water coming through.
  5. Look outside and above. On the other side of that wall, check for cracked plaster, a gap around a window frame, a leaking AC drain or a terrace directly above. Our guides on window frame gaps and AC drain leaks show what to look for.
  6. Check the room's habits. Wardrobe pushed flat against an external wall, closed windows all day, wet clothes dried indoors or a bathroom door left open all feed condensation.

Tip: photograph the corner with the date each morning for a week, and note any rain. Patterns show up quickly.

If the answer looks like a leak

Top-floor bedroom corners usually mean the terrace above, especially near the parapet, so see our guide to the parapet wall base leak. A bedroom directly under another flat can be a different story, covered in ceiling leak from the flat above. A wardrobe that smells damp against an external wall is covered in wardrobe damp smell. In each case the fix is at the entry point, not on the wall surface.

DIY clean or call someone?

Clean it yourself if

  • The patch is small and looks like scattered dots with no stain or peeling paint.
  • The wall is dry to the touch and stays dry after rain.
  • Better ventilation and moving furniture a few inches off the wall makes it stop returning.

Wear a mask and gloves, keep the window open, and wipe with a mild detergent solution on a damp cloth. Dry the area thoroughly afterwards. Do not mix cleaning chemicals.

Call for an inspection if

  • The mould returns within days or weeks after cleaning.
  • There is a stain with an edge, bubbling paint or a soft, powdery plaster.
  • It grows after rain or spreads along the ceiling.
  • The affected area is bigger than a few hand-widths.

What not to do

  • Do not paint over it. Paint seals moisture in, and the patch reappears and peels. Dry the wall and fix the source first.
  • Do not scrub dry mould vigorously. Dampen it first so you are not throwing spores into the air.
  • Do not use a heater or fan as the fix for a leak. It may dry the surface while water keeps arriving behind it.

Health note. Damp and mould can irritate some people, particularly those with breathing sensitivities. This is general information, not medical advice. If someone at home is affected, speak to a doctor, and treat the damp at its source.

Where LoklFix fits

We trace the moisture to its source, whether that is the terrace, an outer wall, a window, a pipe or condensation, before suggesting any work. If it is just airflow, we will tell you.

Mould back after you cleaned it? Send photos on WhatsApp, or call +91-8123083393 for a free inspection this week.

Frequently asked questions

Can I just wipe off the mould and repaint?+

Wiping a small patch is fine, but repainting without finding the moisture source means the mould usually returns under the new paint. Fix the cause first, let the wall dry fully, then repaint.

Why is mould only in the corners?+

Corners have less air movement and are often cooler, especially where two external walls meet, so moist air settles and condenses there. Corners near a terrace, parapet or bathroom can also be where a leak shows first.

Is bedroom mould harmful?+

Damp and mould can irritate some people, particularly those with breathing sensitivities. This is general information and not medical advice. If anyone in the house is affected, speak to a doctor and fix the damp at its source.