Why Is My Wall Damp? How to Find the Cause in a Delhi Home

Free checks: where the patch is, and when it gets worse

Do these before you let anyone open a wall. They cost nothing, most take minutes, and between them they point at one of the four sources far more reliably than a glance from a contractor.

• 1. Measure the height off the floor. Damp that stops in a fairly level band roughly knee height or lower, all along a wall, behaves like rising damp. Damp high in a ceiling corner comes from above. A patch floating in the middle of a wall with dry plaster all around it is usually a pipe.
• 2. Look at the shape. A soft-edged, roughly round patch that spreads outwards suggests a point source, such as a leak. A long even band suggests ground moisture or a slab. A wide film of moisture with black speckling in a corner, mostly on the surface, suggests condensation.
• 3. Feel it, and feel the wall a metre away. Damp plaster feels cooler and heavier. If the whole wall feels cold but only the corner is wet, that is a temperature story, not a plumbing one.
• 4. Walk around the wall. Note what backs onto it: a bathroom, the kitchen sink, an outside face, a stair shaft, or the neighbour’s bathroom in a shared wall. Note the floor you are on and whether there is a terrace above.
• 5. Tape a sheet of plastic over the patch. Tape a piece of clear plastic tightly to the wall on all four sides and leave it a day or two. Water droplets on the room side means moisture is coming out of the air — condensation. Water on the wall side, with the plastic dry, means moisture is coming through the wall.
• 6. Keep a two-week note. Write down when the patch looks worse. This one test does more than all the others put together, and the next section explains why.

If the patch already has black fuzzy growth on it, read black mould on walls alongside this page.

The timing test: when does it get worse? This is the most useful thing on the page. Damp from different sources responds to different triggers, so watching when it worsens separates them almost on its own.

• Worse a few hours to a day after rain, better in dry weather. That is water coming in from outside — a terrace slab, an exterior wall face, a cracked parapet, a blocked balcony drain, a window frame. Penetrating damp lags behind the rain rather than tracking it exactly, because the water has to travel through masonry.
• Worse after someone showers, runs a tap or uses the washing machine, and unrelated to weather. That is plumbing. Try not using the suspect bathroom for a full day and see whether the patch dries at the edges, then use it normally and watch it return.
• Worse overnight in winter, especially on an outside wall or in a corner, and better once windows are opened. That is condensation. It shows up on cold mornings from about November, eases in summer, and is worst in rooms that are closed up with the windows shut.
• The same in May as in August, no matter what anyone does. That is either a concealed leak running constantly or ground moisture. Neither cares about the weather, which is exactly what makes them identifiable.
• Only in the monsoon, every year, same place. Rain finding the same route in every year. It is being fixed with paint each time instead of being traced.

Is it a plumbing leak? The shared bathroom wall case

This is the classic Delhi flat problem and the one most often misdiagnosed as seepage. Your bedroom wall is very often the back of a bathroom — yours, or the flat next door, or the flat above.

• What it looks like. A patch that grows outward from a point, usually on the wall shared with a wet room, sometimes at mid-height where a concealed pipe runs. Plaster may sound hollow when tapped. Paint bubbles before it flakes.
• How to confirm it. The timing test above. Also check whether the damp is directly behind a shower, a mixer, a flush tank or a floor trap on the other side. Height on your side often matches fitting height on theirs.
• The neighbour problem. Failed waterproofing under someone else’s bathroom floor seeps sideways into your plaster while their bathroom looks perfectly normal. Nothing on their side looks wrong, which is why these conversations go badly. Take photographs with dates, and show the pattern over two weeks rather than one damp day.
• Water tanks and risers. An overflow from an overhead tank, or a leaking riser in a common shaft, can wet the same wall on several floors at once. If a neighbour above or below has the same patch, that is your answer and it is a building matter, not a flat one.
• Is it DIY? No. Tracing a concealed leak and opening plaster to reach it is a plumber’s job. If the source is a bathroom above or beside you, bathroom waterproofing explains what the real repair involves.

Is it rain coming in, or damp rising from the ground?

Both bring water through the masonry, but they arrive from opposite directions and behave differently, so they are easy to separate once you know what to look for.

• Penetrating damp comes in sideways or from above. Driven monsoon rain on an unsealed exterior wall, a terrace slab with tired waterproofing, a cracked parapet or chajja, a blocked balcony outlet, or a gap around a window frame or an AC pipe sleeve. It follows rain with a lag of hours or a day, and it appears on the face of the building that takes the weather.
• The top-floor version shows up in ceiling corners and along the tops of walls. See terrace waterproofing and living on the top floor in Delhi.
• Rising damp comes up from the ground. Ground floor and basement rooms only, in a band along the bottom of the wall that stops at a fairly consistent height. It is present all year, does not care about rain, and is often worst behind furniture pushed against an outside wall.
• Everyday water makes rising damp worse. Daily wet mopping right against the skirting, a planter standing on the floor, or a garden bed built up against an outside wall on the other side all feed it.
• Cracks are a route, not just a symptom. A crack on an exterior face lets rain in directly. Cracks in walls covers which ones matter.
• Is it DIY? Clearing a blocked balcony or terrace outlet is. Sealing a terrace, an exterior face or a structural crack is not, and doing it in the wrong season wastes the work — see the best time to paint and waterproof.

Is it condensation? The one that is not a leak at all

Condensation is the odd one out, and it is the one people spend the most money mistakenly waterproofing. The water was never in the wall. It came out of the air in the room and settled on a cold surface, the same way a bottle taken out of the fridge goes wet on the outside.

• What it looks like. Surface wetness rather than soaked plaster. Cold outside walls, corners, behind an almirah, behind a bed pushed against a wall, and around window reveals. Often black speckled mould on the surface with the paint still firmly attached underneath.
• When it happens. Delhi winter mornings, in closed rooms. It builds overnight and clears when the room is opened up. It largely disappears in summer, which is the opposite of seepage.
• What feeds it. Drying clothes indoors, cooking without an exhaust, bathing without a window or exhaust fan, and keeping every window shut through smog season. All of it puts water into the air, and the coldest wall in the flat collects it.
• The plastic sheet test settles it. Droplets on the room side of the taped plastic means the water is coming from the air.
• Is it DIY? Largely yes. Ventilate after bathing and cooking, use the exhaust fan and leave it running a few minutes longer, dry clothes on the balcony where the air outside allows, and pull furniture a few inches off cold outside walls so air can move behind it. If a cold outside wall is the culprit, why your wall feels hot or cold explains why that wall is the coldest one.

When to call someone, and what to tell them

Call once your timing note points at a source, or straight away if any of the following apply: plaster is soft or bulging, damp is spreading month on month, it is near a distribution board, socket or wiring, or a neighbour above or below has the same patch.

• Call a plumber if the patch is unaffected by weather, or clearly linked to a bathroom, kitchen or tank on the other side.
• Call a waterproofing contractor if it follows rain, if you are top floor with damp in ceiling corners, or if it returns every monsoon in the same place.
• Call an electrician first if damp is anywhere near a switchboard, socket or light point. Do not work around wet electrics yourself.
• Do not call a painter first, for any of these. Painting is the last step after the wall is dry, never the first.

Tell them this and they will arrive with the right equipment:

• Which floor you are on and whether there is a terrace above.
• What is on the other side of the wall.
• Height and rough size of the patch, and whether it is growing.
• Your two-week note: worse after rain, after someone bathes, or on winter mornings.
• Whether the plastic sheet showed droplets on the room side or the wall side.
• Whether the plaster is soft, and whether there is white powder, bubbling or mould.

Once the source is stopped, let the wall dry fully before anyone paints — that can take weeks, not days. Paint peeling off walls and paint bubbling on walls cover why repainting too early fails. Monsoon waterproofing tips covers what to check before the rain arrives.