The Coating Selection Map: Matching Surface Treatment to Environment
Surface treatment selection is environment matching, not preference. A map from mildest to harshest duty keeps specifications honest and budgets sane.
Bottom line: for most Surface Treatment applications the decision comes down to load, environment and assembly method — the Surface Treatment guide walks through the selection.
The map
- C1–C2 (indoor, dry/urban): trivalent blue or black zinc, 96–200 h NSS — consumer electronics, office equipment.
- C3 (industrial/semi-outdoor): sealed zinc or zinc-nickel, 240–480 h — machinery, automotive interior-adjacent, telecom indoor cabinets.
- C4 (coastal/road salt): zinc-nickel or zinc-flake, 480–720 h — automotive chassis, outdoor enclosures, rail.
- C5 (marine/offshore): zinc-flake high-build, duplex systems, or A4/6-moly stainless — coastal structures, marine equipment.
- Chemical/food/medical: passivated stainless or PEEK — where chemistry, not weather, is the enemy.
Beyond corrosion: friction and appearance
The same map must respect torque behavior (zinc-flake topcoats stabilize friction) and cosmetics (PVD and anodizing for visible joints). Topprecision applies the full finish spectrum in controlled partner lines, publishes environment-class data per finish, and reviews customer exposure profiles to pick the least expensive compliant option — not the most expensive habit.
Coating selection by environment
| Coating | Salt spray (hours) | Hydrogen risk | Best environment |
|---|---|---|---|
| Zinc plating (clear) | 48–96 | Yes (high-strength) | Indoor, general |
| Zinc-nick (12–15% Ni) | 200–500 | Moderate | Automotive underbody |
| Dacromet / Geomet | 500–1000+ | None | Wind, solar, outdoor steel |
| Hot-dip galvanized | 1000+ | None | Structural, coastal |
| Mechanical galvanized | 300–600 | Low | 10.9/12.9 grade outdoor |
Need corrosion protection for your fasteners?
Toprecision applies zinc, zinc-nick, Dacromet/Geomet, hot-dip galvanizing, PTFE, DLC and PVD coatings in-house, with ISO 9227 salt-spray testing up to 1000+ hours. Send the environment and required salt-spray hours — we will recommend the coating and supply test reports. Request coating selection support.
