Light fittings by the sea: salty air and corrosion

Salty coastal air can ruin an ordinary outdoor fitting within a few seasons. A practical guide to materials, coatings, fixings and maintenance.

Fittings installed at a seaside cottage on the Caspian, a promenade café or a balcony facing the water face a tougher test than those in town. Sea wind carries salt as spray and mist, the salt settles on metal surfaces, and together with moisture it speeds up corrosion. The results are blisters on the housing, rust on fixing screws and blackened contacts inside.

How salt accelerates corrosion

Metal needs moisture and oxygen to corrode, and salt helps in two ways. First, salt crystals draw moisture from the air and keep a thin film of electrolyte on the surface even when it looks dry. Second, chloride ions locally break down the natural protective oxide layer on aluminium and stainless steel. The result is pitting: a spot that looks like a small blemish from outside turns into a deep pit underneath.

Where different metals meet, such as an ordinary steel screw in an aluminium housing, salty moisture also drives galvanic corrosion. The more active metal, usually the aluminium, is eaten away quickly around the screw.

Housing material and coating

When choosing a fitting for a coastal area, pay attention to the following:

• An aluminium housing must have a good-quality finish, usually powder coating or anodising. Corrosion starts wherever the finish is cracked or scratched.
• Stainless steel comes in different grades. Grades with added molybdenum, such as type 316, resist chloride environments better than ordinary type 304.
• Polycarbonate and other plastic housings do not rust, but plastic without UV stabilisation yellows and turns brittle under strong coastal sunlight.
• Some coatings have their corrosion resistance rated to a standard. ISO 12944 classifies environments by corrosivity, and the seaside falls into the higher categories. If a manufacturer provides this information, favour it.

Fixings and cable entries

Often the housing survives but the screws holding it to the wall, the bracket or the bolts at the base of a post rust away. A few years later the fitting starts to sway in the wind, or the screws cannot be undone for maintenance.

• Choose fixings in a corrosion-resistant metal compatible with the housing.
• Put insulating plastic washers or spacers between dissimilar metals.
• Applying an anti-seize or anti-corrosion compound when fitting screws makes them easier to remove later.
• At cable entries, UV-resistant plastic or nickel-plated glands last longer than bare metal ones.

Protection rating and condensation

For coastal fittings, IP65 or higher makes sense, because wind drives spray from every direction and under pressure. Tightness has a downside, though: a housing that warms by day and cools at night can trap salty moisture inside. Good coastal fittings have a membrane breather that equalises pressure without letting water in.

Rubber gaskets also harden prematurely in salt and sun. Silicone gaskets usually stay flexible longer in these conditions.

Location affects the outcome as well. A wall facing the sea and exposed to the wind receives many times more salt than the back of the building. Where possible, placing a fitting under the eaves or on the sheltered side extends its life. Ground-mounted lights face extra trouble from sea sand and salty puddles, so they belong in well-drained spots where water does not collect. Glass covers also turn cloudy under a salt film that absorbs part of the light, which makes washing a matter of light quality as well as corrosion protection.

Maintenance schedule

On the coast, the cheapest and most effective protection is regular washing.

• Rinse fittings with fresh water, especially after windy periods, to remove the salt film. Do not aim a high-pressure jet straight at the gaskets or cable entry.
• Once or twice a year, check the finish for scratches, blisters and rust spots, and touch up small damage in good time with paint recommended by the manufacturer.
• Inspect screws and brackets and replace any rusted component without delay.
• When a fitting has to be opened, switch off the circuit first. White salt traces or a green deposit inside mean the contacts need cleaning and the gasket needs replacing.

Electrical safety on the coast also needs extra attention: earthing metal fittings and protecting the circuit with an RCD matter even more here than in ordinary conditions. Powerful Zəfər İşığı LED lamps exist for lighting larger outdoor areas; by the sea, the fitting they go into must be chosen for these conditions.