Coatings Knowledge
METALLIZING VS. GALVANIZING
Both processes protect steel with sacrificial zinc. The right choice comes down to the size of the structure, where the work has to happen, and how much control the specification demands.
The short answer: hot-dip galvanizing suits high volumes of small parts that fit in a kettle. Thermal spray metallizing is the choice for large structures, field work, distortion-sensitive fabrications, and projects that need a specified coating thickness or same-day topcoating — which is why DOTs increasingly specify metallizing for steel bridges.
HOW EACH PROCESS WORKS
Thermal Spray Metallizing
The steel is abrasive blasted to a near-white finish, then zinc, aluminum, or 85/15 zinc-aluminum wire is melted by an electric arc and propelled onto the surface. The substrate stays near ambient temperature, the coating bonds mechanically, and the structure can be handled or sealed immediately. Applied in the shop or in the field under SSPC-CS 23.00 / AWS C2.23.
Hot-Dip Galvanizing
Fabricated steel is cleaned, fluxed, and immersed in a bath of molten zinc at roughly 830–850°F. The zinc reacts with the steel to form bonded zinc-iron alloy layers per ASTM A123. It is a batch process performed at a galvanizing plant, so part size is limited by the kettle and finished parts must be shipped back to the site.
SIDE-BY-SIDE COMPARISON
| Factor | Thermal Spray Metallizing | Hot-Dip Galvanizing |
|---|---|---|
| Process | Zinc, aluminum, or 85/15 zinc-aluminum wire is melted by electric arc and sprayed onto abrasive-blasted steel | Steel is dipped in a bath of molten zinc at roughly 830–850°F |
| Size limits | None — applied to structures of any size, in the shop or in the field | Limited by kettle dimensions; oversized members must be double-dipped or redesigned |
| Heat distortion | Substrate stays near ambient temperature — no warping of thin or asymmetric sections | Immersion in molten zinc can distort thin plates and welded assemblies |
| Thickness control | Applicator-controlled; sprayed to the thickness the specification requires | Governed largely by steel chemistry and immersion time (ASTM A123) |
| Field application | Yes — existing structures, bridges, and repairs can be metallized in place | No — parts must be transported to a galvanizing plant |
| Handling and topcoating | No cure time; the coating can be handled and sealed or topcoated immediately | Surface must weather or be prepared before paint will adhere reliably |
| Corrosion protection | Sacrificial galvanic protection; duplex (sealed) systems support 100-year bridge service-life targets | Sacrificial galvanic protection with a metallurgically bonded zinc-iron alloy layer |
WHEN METALLIZING IS THE RIGHT CALL
- Bridge girders, sheet piling, and structural members too large for a galvanizing kettle
- Thin, welded, or asymmetric fabrications where kettle heat would cause distortion
- Existing structures that must be protected in place — no disassembly or transport
- Projects on a schedule: metallized steel can be sealed, topcoated, and shipped the same day
- Specifications calling for a defined coating thickness or a duplex metallizing-plus-seal-coat system
WHEN GALVANIZING MAKES SENSE
- High volumes of small, standardized parts — bolts, grating, hardware
- Components that fit a kettle and tolerate immersion heat without distortion
- Applications where a metallurgically bonded zinc-iron layer is specifically required
THE DUPLEX ADVANTAGE
Metallizing pairs naturally with a seal coat or full paint system applied the same day — a duplex system. The metallized layer provides sacrificial galvanic protection while the sealer blocks moisture from reaching it, extending service life well beyond either system alone. Duplex metallizing systems are the basis for the 100-year service-life targets now common on steel bridge projects.
Regal Industrial applies 99.9% zinc, 85/15 zinc-aluminum, and 1150/1350 aluminum wire as an SSPC-QP6 certified metallizing contractor, with shop metallizing at our facilities and field metallizing crews for structures that can't come to us. Learn more about our thermal spray metallizing services.
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