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Is Galvanised Steel Rust-Proof for Saltwater-Exposed Sites
Want to know if galvanised steel is rust-proof when on saltwater-exposed sites? If you have worked near the sea, you will have seen how quickly moisture and salt accumulate on surfaces and how this can shorten the service life of unprotected steel. Coastal air typically contains higher humidity and salt particles, so marine corrosion can begin earlier and progress more quickly.
The Environment Agency’s Toe Structures Management Manual, based on ArcelorMittal guidance and Eurocode 3, sets typical corrosion rates for unprotected steel piles in seawater [1]. In high-attack tidal zones, seawater can remove about 1.9 mm of steel in 25 years and 7.5 mm in 100 years, with about half that loss when piles are permanently immersed. A galvanised coating adds a protective zinc coating that helps the steel resist these conditions and supports long-term coastal protection.
This article explains how zinc coatings, duplex systems and specification choices support long-term performance in marine environments.
How Coastal Environments Accelerate Corrosion on Bare Steel
Coastal areas create conditions that accelerate corrosion of unprotected steel. Higher humidity levels and regular dampness mean moisture remains on metal surfaces for longer. The Met Office provides long-term UK climate maps for temperature, rainfall and sunshine using the HadUK Grid dataset, with anomalies shown against the 30-year periods 1961 to 1990 and 1991 to 2020 [2].
These maps include all forms of precipitation such as rain, snow and hail and are updated annually as new data becomes available. By comparing seasonal and annual rainfall and sunshine maps, it is possible to identify areas that experience frequent wetting and fewer drying periods.
In coastal regions, more frequent rainfall and longer periods of dampness increase the time bare metal remains wet, which can accelerate corrosion if no protective system, such as galvanising, is in place.
What You Need to Check Before Specifying Coastal Steel
When planning coastal projects, it helps to assess how close the structure is to the shoreline, how often it will be exposed to spray and how much wind-driven salt the location receives. These factors influence the required level of protection and whether thicker galvanising or additional coatings should be considered for your coastal protection strategy.
How a Zinc Coating Protects Steel in Marine Conditions
Hot-dip galvanising protects steel by forming a metallurgically bonded zinc coating on its surface. The steel is dipped in molten zinc, so a series of zinc-iron alloy layers forms, creating a continuous barrier between the steel and the surrounding environment. This coating provides both barrier and sacrificial protection, which is especially valuable where salt and moisture are present along the coast.
The main standard for hot-dip galvanised coatings in the UK is EN ISO 1461. Guidance from the Galvanizers Association explains that this standard sets minimum coating thicknesses linked to steel section size [3]. For example, steel sections thicker than 6mm are required to achieve a typical mean coating thickness of around 85 microns, while thinner sections have slightly lower minimum values.
When working in marine and coastal locations, specifying a coating that meets or exceeds these minimum thicknesses helps provide a predictable service life. Thicker zinc layers generally supporting longer periods of corrosion protection.
When a Duplex Coating Gives Extra Confidence by the Sea
In some coastal locations, a galvanised coating on its own may be exposed to:
- Frequent salt spray
- Wind-driven sand
- Regular water contact
In these cases, a duplex system can help extend the steel's lifespan. A duplex coating combines hot-dip galvanising with a paint or powder topcoat, providing the steel with an additional protective finish.
The powder or paint layer reduces direct exposure of the zinc coating to the environment. If the outer coating is chipped in normal use, the zinc layer still provides protection underneath. This approach is common for railings, lighting columns, street furniture and access walkways near the sea. Here, both appearance and durability matter.
For projects that require specific sizes before coating, you can order galvanised steel sheet cut to your exact measurements and then apply a suitable topcoat as part of your finishing process.
Simple Ways to Keep Galvanised Steel Performing Near the Coast
Coastal projects benefit when the environment and the coating are considered together. Good design, installation, and ongoing galvanising maintenance help the zinc layer perform as intended, especially in areas close to the shoreline where salt and moisture accumulate more frequently.
Practical Steps for Day-to-Day Galvanising Maintenance
- Allow water to drain easily by avoiding design features that trap moisture.
- Seal cut edges or drilled areas with a suitable repair coating to maintain protection.
- Keep surfaces clean by rinsing off salt deposits during routine maintenance.
- Inspect fittings, joints and fasteners periodically and address any coating wear early.
- Choose compatible fixings and accessories to reduce the risk of contact corrosion.
These steps help the coating remain intact and reduce the likelihood of corrosion at the most exposed areas of the steel.
When to Choose Thicker Galvanising or a Duplex System
Some locations sit within the area most affected by salt spray and wind-driven moisture. In these areas, a thicker galvanised coating or a duplex system can provide better protection.
This is useful for structures placed close to the sea, like:
- Railings
- Stairways
- Platforms
- Lighting columns
- And more
Choosing the right material and coating level at the start helps the steel remain durable throughout its service life. Our specialised metal processing services supplies aluminium, stainless steel and brass alongside galvanised steel, all cut to your exact measurements.
Plan Stronger, Longer Lasting Coastal Installations
Galvanised steel can provide dependable performance in coastal areas when the coating thickness and maintenance plan match the level of salt and moisture on site. The zinc layer slows corrosion by shielding the steel from regular contact with damp, salt-laden air, and duplex systems or thicker coatings can support longer service life for structures located near the shoreline.
Click Metal supplies galvanised steel cut to your exact measurements for coastal projects such as railings, walkways and general fabrication. The team can discuss your location, exposure level, and planned use to help you select a suitable thickness or finish for your project.
Call 01794 526090 or enquire now to discuss your coastal project, check material options and order galvanised steel sized to your requirements.
External Sources
[2] https://www.metoffice.gov.uk/research/climate/maps-and-data/uk-actual-and-anomaly-maps
[3] https://galvanizing.org.uk/galvanizing-standards/iso-1461/
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