Exterior paint in coastal salt air and 40°C sun: what lasts

Exterior paint near the Nellore coast has to survive three separate attacks: ultraviolet light from a sun that pushes air temperatures past 40°C from March to June, salt carried inland on the sea breeze, and heavy wind-driven rain from October to December. Each of these breaks paint down in a different way, and a product chosen for only one of them fails at the others.

What lasts is a proper exterior acrylic emulsion over correctly prepared, genuinely dry masonry, with every joint, crack and edge sealed before the first coat. The finish matters less than what is under it — but the finish still matters, and interior paint on an outside wall is money thrown away here.

What each factor actually does

UV. Sunlight breaks down the binder that holds pigment in the film. The first sign is chalking: run your palm down a south or west wall and it comes away powdered. Once a wall is chalking, colour is fading and the film is thinning.

Salt. Salt-laden air settles on the surface and works into pores and hairline cracks. It draws moisture, it attacks steel — grilles, railings, window frames, exposed reinforcement — and rust stains bleed through paint from beneath. It also leaves white crystalline deposits on the surface that stop the next coat bonding if they are not washed off.

Rain. Driving north-east monsoon rain finds any unsealed joint. Water behind the film is what causes blistering and peeling, as opposed to the gradual thinning that UV causes.

Heat cycling. A wall at 50°C surface temperature in the afternoon and 27°C at night expands and contracts every single day. A brittle or over-thick film cracks under that; a flexible one absorbs it.

Where exterior failure usually starts

Failures are almost never in the middle of a clean wall. Check these first:

• The parapet and its coping — the most exposed surface on the building.
• Window and door frame joints, and sill undersides.
• Around AC outdoor unit brackets and drain pipes, where steel meets masonry.
• Balcony railings and grilles, where rust bleeds down the wall below.
• The bottom half metre of the wall, splashed by rain off the ground.
• North-facing walls that never dry fully and grow green or black algae.

Any of these, left untreated, will pull a new paint job apart while the rest of the wall is still fine.

Preparation that makes the difference

For coastal exteriors the sequence is longer than most people expect, and skipping any of it shortens the life of the job:

1. Wash the wall properly — not a wipe. Salt deposits, algae and chalk have to come off, or the new coat is bonding to loose powder.
2. Treat algae and fungus where present, then rinse and dry.
3. Rake out and fill cracks. Hairline crazing takes an exterior putty or crack filler; anything wider needs opening up and filling in depth.
4. Deal with rusted steel before painting near it. Rust that is painted over keeps going and comes back through in a season.
5. Prime. An exterior primer suited to the substrate is what the topcoat grips.
6. Two full topcoats, applied at the right spread rate. Thinning paint down to make it go further is the most common way a five-year system becomes a two-year one.

The sun, and the working day

On a hot wall, paint skins over before it can level or bond. In April and May a crew should be following the shade — east walls in the morning, west and south in the late afternoon — rather than painting whichever wall is convenient. It slows the job by a day or two and it is the difference between an even finish and one covered in lap marks.

What you can do, and what to leave alone

You can wash reachable walls, clear algae from a shaded corner, keep rainwater outlets clear, and look over the parapet and window joints after rain to see where water tracks. What is not worth doing yourself is anything at height — parapets, upper-floor walls, terrace edges. Exterior painting on a ladder above the ground floor is how people get hurt, and a wall done badly at height is expensive to redo.

Call someone in when you can see chalking across a whole elevation, when paint is peeling in sheets rather than flakes, when rust streaks are running down from railings, or when a wall is still dark two days after rain has stopped. Waterproofing treatment on the rate card is ₹2,499; paint and materials are charged at MRP and shown to you before work starts.