Hot-dip galvanising vs. Paint
When selecting a surface treatment for steel structures, we often face a dilemma between hot-dip galvanising and conventional coating systems. Both methods have their place in practice, but the choice depends on the specific environment, maintenance requirements and aesthetics. In this text, we summarise the technical principles, service life and economic aspects you should consider before making a decision.
Principle of hot-dip galvanising according to EN ISO 1461
Hot-dip galvanising is a diffusion process in which the steel structure is immersed in molten zinc. Alloy layers of zinc and iron form on the surface, covered by a layer of pure zinc; this is not merely a coating but a metallurgical bond with the material. Standard EN ISO 1461 specifies the minimum coating thickness according to the thickness of the steel component. The advantage is that zinc protects the structure even if the surface is damaged (scratches, cuts), as the zinc sacrifices itself and protects the steel electrochemically.
Outdoor lifespan: zinc versus paint
For outdoor applications, hot-dip galvanising is often the preferred choice for long-term protection. The zinc layer provides corrosion protection for decades without requiring regular maintenance. In contrast, coating systems, whether epoxy or polyurethane paints, gradually degrade under the influence of UV radiation, moisture and temperature fluctuations. Paint may peel, flake or lose its gloss. While zinc offers active protection, paint protects only passively as a barrier. Once this barrier cracks, corrosion spreads beneath the coating, a process that is difficult to stop without completely removing the old layer.
Duplex system: combining advantages
If you need to combine the long service life of zinc with specific colour requirements, the solution is a duplex system. This consists of hot-dip galvanising followed by the application of a coating (typically an epoxy primer and a polyurethane topcoat). This system offers the best combination: zinc ensures long-term corrosion protection, while the paint provides aesthetic appeal and additional barrier protection. It is the ideal choice for bridges, industrial buildings or facades where visual identity and minimal maintenance are paramount.
When is paint the right choice
Painting systems remain indispensable indoors where structures are not exposed to aggressive outdoor conditions. Paint allows for precise adherence to colour codes (RAL) and specific textures, which is crucial for office spaces, shopping centres or residential interiors. On top of that, painting is suitable where hot-dip galvanising would be technically complicated or economically disadvantageous, for example with very large and heavy components that cannot be easily immersed in a bath, or with structures requiring high dimensional accuracy that could be compromised by the zinc layer.
Impact on price
The cost of surface treatment depends on the scope, complexity of components and the required standard. Hot-dip galvanising has higher initial costs but lower total lifecycle costs due to minimal maintenance. Painting systems are often cheaper initially but require regular renewals, which increases the overall cost in the long term. Duplex systems carry the highest price but offer the highest level of protection and aesthetics. Specific price differences depend on the amount of steel and structural complexity; therefore, we recommend requesting a quotation so we can provide precise costs for your specific project.