Damp patches and seepage: why painting over them never works

Painting over a damp patch buys you a few weeks. The patch is not a stain, it is the visible end of water that is arriving from somewhere, and paint is a thin film with no ability to hold water back. The new coat traps the moisture, the moisture pushes the coat off the plaster, and by the next monsoon the patch is back — larger, because the trapped water spread sideways while it was hidden.

So the first job is not paint. It is finding where the water is coming from. Until that is answered, any money spent on finish coats is spent twice.

Reading the patch

The shape and position of a damp patch usually tells you the source.

• A patch on the ceiling or the top of a wall, worse after rain. Terrace or roof. Ponding water, a failed slab joint, a cracked parapet, or a blocked rainwater outlet that lets water stand.
• A horizontal band a foot or two above the floor, present all year. Rising damp — groundwater drawn up through the plinth. Common in older ground-floor rooms and in walls where the outside ground level has been raised by later paving.
• A patch shared between a bathroom wall and the room next door. A leak in a concealed pipe, or grout and waterproofing failure in the wet area.
• A vertical stripe running down an internal wall. Usually a pipe or a channel in the wall behind it.
• A patch on an external wall only during the north-east monsoon. Wind-driven rain finding a hairline crack, an unsealed window frame joint, or plaster that has lost its bond.

In Nellore the October to December rain does the diagnosis for you. Walk the house during a heavy spell and note where patches appear and how quickly. That is far more useful than looking at a dry wall in May.

What has to happen before any paint

The repair order does not change:

1. Stop the water. Seal the terrace or the crack, fix the pipe, clear the outlet, repoint the parapet. This is the actual repair, and it happens outside or inside the structure, not on the paint surface.
2. Let the wall dry. Weeks, not days. Painting a wall that still holds water re-creates the original problem.
3. Remove everything loose. Scrape back to sound plaster. If plaster sounds hollow when tapped, it has lost its bond and must come off — paint over hollow plaster falls off with the plaster.
4. Treat and re-plaster where needed, then apply a suitable primer.
5. Then the finish coats.

Skip step one and the rest is decoration.

What you can check yourself

• Look at the terrace after rain. Standing water that does not drain within a few hours means a slope or outlet problem, and it is the single most common source of top-floor damp.
• Check that rainwater outlets and downpipes are not blocked with leaves or a bird's nest.
• Run a finger along the joint where window and door frames meet the wall outside. An open, crumbling gap there lets wind-driven rain straight in.
• Tap the wall around the patch. A hollow, drummy sound means the plaster has gone.
• Look at the wall from outside for the first time in years. A hairline crack running down from a window corner is a classic entry point.

What not to do: do not chase a suspected pipe leak by breaking into a wall yourself, and do not go up on a wet terrace parapet to inspect it. Both are jobs for someone with the right footing and tools.

When to call someone in

Call if the patch is growing, if it comes back every monsoon in the same place, if plaster is powdery or falling, if there is black growth on the surface, or if the wall next to a bathroom or kitchen is soft. Those are signs that the water is still arriving, and someone needs to trace it before a brush is opened.

Waterproofing on our rate card is ₹2,499 for a terrace or bathroom anti-seep treatment. If a room has to be repainted after the repair, a single room is ₹3,499, and a 1BHK interior in primer plus two coats is ₹8,999. Materials are charged at MRP and shown to you before work begins. A quote given without anyone having looked at where the water is coming from is a quote for the wrong job.