By the sea, anti-corrosion treatment is sized on the corrosivity of the site: the strip within 500 m of the coast counts as a very aggressive marine atmosphere, classified C5-M under ISO 12944. On steel, the system that holds is a zinc-rich primer, an epoxy intermediate and then a polyurethane finish, for a total dry film thickness of 200 to 320 µm, checked with a gauge and not by eye. Exposed screws and hardware move to A4 stainless steel, meaning 316L, and mixed assemblies of galvanised steel, aluminium and copper are isolated with a washer or a gasket to avoid galvanic corrosion. A heat pump outdoor unit installed facing the spray is ordered in its marine version, failing which the exchanger pits within a few seasons and the warranty does not follow.
Understanding coastal corrosion: salt, humidity and wind
Why salty air speeds up metal oxidation
By the sea, salt settles as micro-droplets. With humidity, it forms a conductive film that facilitates electrochemical reactions. Chloride ions attack certain protective layers and promote pitting corrosion. The wet-then-dry cycles, very frequent near the ocean, accelerate the phenomenon further.
The most exposed areas on a coastal house
The most affected are surfaces directly facing sea spray and wind. Watch windward facades and all metal elements first.
- Roof fixings, edges, guardrails, gates
- Gutters, downpipes, grilles, outdoor light fixtures
- Joinery hardware, shutters, locks
- Outdoor air-conditioning or heat pump units
Spotting the early warning signs before damage sets in
Stay alert to the first traces. Blistering paint, rust streaks, black spots, or small craters on stainless steel are warning signs. On aluminium, a powdery white film can appear. An inspection after strong winds and a freshwater rinse often keep things from getting out of hand.
Diagnosing and preparing a coastal job site (2026 field method)
Taking stock: metals, fixings, substrates and critical points
By the sea, salt speeds up corrosion and reactions between metals. Start by identifying sea-spray zones, rust traces, mixed fixings (stainless steel, galvanized steel, aluminium) and critical points. Think about cuts, drill holes, guardrail joints, post bases. Test the adhesion of old coatings and check the moisture level of substrates. This survey can be documented from a phone, with Argile attaching photos, findings and measurements to the property file.
Choosing the right treatments by substrate: steel, aluminium, wood, concrete
Steel. Stripping or mechanical preparation, then an anti-corrosion system suited to the marine environment (zinc-rich primer, epoxy, finish). Aluminium. Degreasing, sanding, bonding primer, and isolating contact with copper or steel. Wood. Fungicide treatment, appropriate use class, microporous finish. Concrete. Removing chloride-affected zones, repair, then protection with a silane water repellent or coating.
Organizing site protection: storage, tarping, washing and drying
Protect the site from salt-laden wind. Store off the ground, under a breathable tarp, and avoid cardboard, which retains moisture. Plan a freshwater wash of parts before installation, then allow complete drying before bonding, painting or sealing. Keep a clean area for sealants and check the weather to limit rework.
Choosing salt-resistant materials and finishes for coastal jobs
Hardware and fixings: choose the right stainless steel and avoid galvanic couples
In coastal areas, "standard" screws rust quickly. Aim for 316L stainless steel (A4) hardware for exposed parts. And avoid mixing metals. Aluminium, steel, copper and zinc, in contact with moisture, create galvanic couples that accelerate corrosion. Insert insulating washers, sealants or gaskets, and keep metal-on-metal consistency.
Paints, primers and anti-corrosion systems: what lasts over time
What lasts is a complete system. On steel, base it on an epoxy primer, then a polyurethane finish, with careful preparation (degreasing, abrasion, dedusting). On galvanized steel or aluminium, choose compatible primers, and treat chips quickly. A small scratch, with salt, becomes an open door.
Joinery, guardrails, coping: durable options and points of caution
For joinery and coping, aluminium with certified thermal-lacquer coating is a safe bet if cuts and drill holes are protected. For guardrails, 316L stainless steel or well-protected aluminium limit rework. Watch for water traps, plan for slopes and drainage, and advise a freshwater rinse as maintenance.
Building to last: anti-corrosion execution details for coastal work
Waterproofing and water management: limiting stagnation and salty runoff
By the sea, salt gets to work as soon as water stands still. Always give a slope to sills, coping and thresholds. Plan for drip edges and continuous flashing. The goal is simple. Drain fast, with no water path toward the structure. Continuous slope.
Treating cuts, drill holes and welds: the mistakes that cost dearly
Corrosion often starts where steel has been left bare. After every cut or drill hole, deburr, degrease, then touch up the protection system suited to the substrate. On welds, treat the blued zones and spatter, then restore the protection thickness. Immediate touch-ups.
Ventilation and condensation: reducing indoor humidity that feeds corrosion
Less humidity, less attack. Check that the mechanical ventilation system is working, avoid "sealed" rooms without extraction, and address thermal bridges around joinery and fixings. In technical rooms, keep air circulating and avoid storing items in damp conditions. Fresh air.
Maintenance and warranties: securing the durability of coastal work
A simple maintenance plan: rinsing, inspections and touch-ups at the right time
By the sea, salt speeds up the wear of paints, renders and metal parts. Plan a regular freshwater rinse, especially after a windstorm, then a visual inspection every three months. Once a year, check fixings, seals, protection chips and early signs of oxidation. Touch up quickly, before corrosion takes hold.
- Rinse, let dry, check drainage points and areas of standing water.
- Do a localized touch-up with the protection system specified in the quote.
Writing your maintenance notice: protecting your liability and your reputation
Hand over a dated maintenance notice. It states the frequency, approved products (neutral pH, non-abrasive), points to watch, and what counts as routine maintenance. Remind clients that legal warranties exist, but that a lack of maintenance can worsen issues and complicate claims.
Explaining to the client what is normal and what should raise a flag (salt, traces, rust spots)
By the sea, salt traces or a white film after drying can be normal. On the other hand, warning signs should trigger a call. Rust spots, blisters, peeling paint, cracks, water infiltration. The earlier you intervene, the less you have to redo.
