Two protections, two different jobs
A common mistake is assuming good paint is enough to protect an outdoor guardrail. In reality, galvanizing and powder coating meet two distinct needs: galvanizing protects the metal itself against corrosion, powder coating protects and colours the surface. One doesn't replace the other — their combination is what gives lasting protection.
Galvanizing: protection through the material
Hot-dip galvanizing involves immersing steel in a bath of molten zinc. The result isn't a simple surface layer: the zinc forms a metallurgical bond with the steel, which keeps protecting it even if the surface is scratched (the surrounding zinc sacrifices itself first, a phenomenon called cathodic protection). The NF EN ISO 1461 standard (2022 edition) sets the minimum zinc thickness depending on the steel's thickness — from 35 µm for the thinnest pieces to 85 µm for the thickest.
Powder coating: colour and UV resistance
Powder coating is a powder paint, applied by electrostatic spray then oven-cured. It brings colour and good UV resistance, but alone, on bare steel, it doesn't durably protect against outdoor corrosion: a micro-crack in the paint film is enough to expose the metal to moisture. That's why, for outdoor use, it's applied over already-galvanized steel rather than bare steel.
How long does galvanized protection last?
An 85 µm zinc thickness gives an average maintenance-free lifespan of roughly 40 to 70 years depending on environment — more in low-corrosivity settings, less near the coast or in industrial areas. One caveat though: many decorative wrought-iron balusters are under 6mm thick, and therefore sit in the standard's lower tiers (35 to 70 µm), not the maximum tier — a nuance worth keeping in mind rather than an unqualified "100 years" claim.
Does an indoor guardrail need both?
Generally not. An indoor stair guardrail, sheltered from moisture and weather, is most often fine with powder coating alone or a blackened finish — galvanizing becomes mainly relevant for any structure directly exposed to the weather (balcony, terrace, facade window). See our installation and finishes page for the detail on the three options.
Frequently asked questions
Can you powder-coat without galvanizing first, for outdoors?
It's technically possible, but not recommended for a structure durably exposed to the weather: anti-corrosion protection then relies solely on the paint film's integrity, which eventually cracks over time.
Does galvanizing change the metal's appearance?
Yes, zinc gives a characteristic matte grey look, visible before powder coating is applied — it's an intermediate step, not the structure's final finish.
How long before a galvanized and powder-coated guardrail needs repainting?
The powder coating itself may need an aesthetic refresh before the zinc's anti-corrosion protection is compromised — the exact timeframe depends on exposure and upkeep, assessed case by case.