Coastal and marine exposure

Why salt spray gets under paint on coastal metalwork

Airborne salt settles on railings, gates and balustrades within a few hundred metres of the shore and keeps working long after the rain has stopped. It draws moisture to the metal surface even through an intact-looking film, which is why coastal ironwork rusts from underneath before the topcoat shows a mark.

Corroded balustrade railing being ground back to bare metal on a seafront balcony

How the corrosion actually starts

Salt is hygroscopic, meaning it pulls moisture from the air even on dry days. Once a few crystals sit on bare or thinly primed steel, they hold a film of damp against the metal permanently, and rust begins under the paint rather than on its surface. By the time bubbling is visible, the corrosion is already established beneath it.

Preparation has to remove salt, not just old paint

Grinding back to bright metal is only half the job if salt residue is left on the surface or trapped in pitting. We wash down with fresh water before any mechanical preparation and again immediately before priming, because a primer applied over residual chloride will fail early regardless of its quality.

Fresh-water rinse before grinding and again before priming
Pitted areas ground back further than a cosmetic pass would need
Primer applied the same day preparation is finished

Choosing a system built for chloride exposure

A zinc-rich or epoxy primer with a polyurethane topcoat holds up far better on an exposed railing than a general-purpose metal paint, and it is worth the extra cost on anything within sight of the water.

Zinc-rich primers give sacrificial protection where the film is scratched
Polyurethane topcoats resist UV chalking better than alkyd finishes
Recoat intervals shortened on the seaward face compared with sheltered sides

How we work on this

We rinse and re-rinse metalwork before mechanical preparation to remove chloride, not just loose paint.
We specify zinc-rich or epoxy primers on exposed steel rather than defaulting to a general metal paint.
We grade each railing or gate on an exposed elevation separately from sheltered runs on the same property.

Questions we are asked about this

Why does my railing rust even though the paint looks fine?

Corrosion often starts under an intact film once salt has drawn moisture to the metal. The paint can look sound for months while rust spreads beneath it, then fail suddenly at a weld or fixing point.

Does washing metalwork down help between repaints?

Yes, a periodic fresh-water rinse removes surface salt before it has time to work into any small breaks in the film, and it costs nothing beyond the time to do it.

Is galvanising better than paint near the coast?

Galvanising resists corrosion well but still benefits from an overpaint system in a marine setting, since galvanising alone can white-rust in salt air over time.