Duplex Life Estimator
Paint over galvanizing doesn't just add its life to the zinc's — the two protect each other, and the combination outlasts the sum. Enter the zinc coating, the environment and the paint system you'd specify, and see the range.
Why duplex beats the sum of its parts
ISO 14713-1:2017 (clause 6.5) puts it plainly: the total life of a zinc coating plus an organic coating is usually significantly greater than the sum of the two lives. The mechanism runs both ways — the zinc stops the paint film under-rusting, and the paint keeps the zinc from corroding early. The multiplier itself isn't an ISO number; the 1.5–2.3 band used here is published guidance (Van Eijnsbergen).
The catch worth knowing
Longer total life doesn't mean you touch it less often. ISO 14713-1 notes that a galvanized coating alone may be recommended for 20 years or more to first maintenance, while the same coating under paint is recommended for only about 10 years — because the paint's appearance degrades first. Duplex buys durability, but the first maintenance visit is usually a repaint driven by looks, not by zinc loss. Do it while the zinc is still intact (ideally with 20–30 µm remaining) and the system keeps its advantage.
Members get the full comparison
- Duplex vs galvanizing-only vs paint-only, side by side
- Specification Summary PDF for the project file
- All 6 professional plant tools with exports
Questions
What is a duplex coating system?
Hot-dip galvanizing with an organic coating (paint or powder) applied over it. ISO 14713-1 uses the term for the combination; ISO 12944-5 and EN 13438 cover the organic coatings applied over galvanizing.
Why does duplex last longer than galvanizing plus paint added together?
Because they protect each other. ISO 14713-1 clause 6.5: the total life of zinc plus an organic coating is usually significantly greater than the sum of the two lives — the zinc reduces under-rusting of the paint film, the paint preserves the zinc from early corrosion. Published guidance puts the synergy at roughly 1.5–2.3× the sum.
When is first maintenance on a duplex system?
Often sooner than the zinc needs it — the paint's appearance drives the decision. ISO 14713-1 notes zinc alone may be recommended for 20 years or more to first maintenance, while the same coating under paint is recommended for only ~10 years, for reasons of paint appearance.
Is the 1.5–2.3 synergy factor an ISO value?
No. ISO 14713-1 confirms the synergistic effect but publishes no multiplier. The 1.5–2.3 band is published guidance (Van Eijnsbergen). Treat the output as a planning estimate, not a warranty.