Zinc Arc Spraying — Galvanising Alternative

What Is Zinc Arc Wire Spraying?

Zinc arc wire spraying — also called zinc metallising or thermal spray metallising — is a corrosion protection process used across Auckland for structural steel, marine fittings, and industrial equipment. Two zinc wires are fed into a spray gun and melted by an electric arc. Compressed air then atomises the molten zinc and propels it onto the steel surface at high velocity. The zinc particles flatten on impact and build up into a dense, bonded coating.

The result is a tough zinc layer that provides sacrificial corrosion protection. If the coating gets scratched or damaged, the surrounding zinc corrodes preferentially instead of the steel underneath. This is the same principle that makes galvanising work — but zinc arc spraying does it without a dip tank.

The steel must be properly prepared first. We abrasive blast all surfaces to a minimum of SA 2.5 (near-white metal) before spraying. Good surface preparation is the single biggest factor in coating performance, and it is something we take seriously.

Zinc Arc Spraying vs Hot Dip Galvanising

Hot dip galvanising has been the default corrosion protection method for structural steel in New Zealand for decades. It works — but it has real limitations that zinc arc spraying avoids. If you have been specifying galvanising out of habit, it is worth understanding the differences.

Factor	Zinc Arc Spraying	Hot Dip Galvanising
Size limits	No size restrictions — can handle any piece	Limited by bath dimensions; oversized items need double-dipping or cannot be done
Heat / distortion	Minimal heat input — no immersion in molten metal	Full immersion at high temperature can cause warping, especially on thin or asymmetric sections
Finish quality	Consistent, even coating; good base for overcoating	Can produce drips, runs, and rough spots; uneven thickness at edges and corners
Paintability	Excellent adhesion for powder coating or paint topcoats	Requires additional surface preparation (etch primer or sweep blast) before painting
Coating thickness control	Precise control to specification	Variable — determined by steel chemistry, immersion time, and bath conditions
Turnaround	Blast and spray in one facility — no transport to a galvaniser	Requires transport to and from galvanising plant; scheduling dependent on galvaniser
Repair / touch-up	Damaged areas can be re-blasted and re-sprayed on site	Touch-up limited to zinc-rich paint; re-galvanising requires full re-dip

For many applications — particularly structural steel, large fabrications, and anything that will be overcoated — zinc arc spraying is the smarter choice. It gives you the same sacrificial zinc protection without the constraints of a dip tank. Read more in our detailed comparison of zinc spraying vs galvanising.

Benefits of Zinc Arc Spraying

There are good reasons zinc arc spraying is increasingly specified by engineers and fabricators across New Zealand:

• No bath size limits: If you can fit it in our workshop, we can coat it. There is no maximum size constraint like a galvanising bath imposes. Large beams, trusses, and structural members are no problem.
• Less heat distortion: Because the steel is not immersed in molten zinc, there is far less risk of warping. This matters on thin sections, hollow sections, and anything where dimensional accuracy is important.
• Better finish for overcoating: The slightly rough profile left by zinc arc spraying provides an ideal key for powder coating or wet paint. Duplex systems (zinc plus topcoat) last significantly longer than either coating alone.
• Sacrificial protection: Like galvanising, the zinc coating corrodes preferentially to protect the steel. Even if the coating gets scratched, the surrounding zinc will protect the exposed steel.
• Handles large structural pieces: Portal frames, long beams, bridge components, and oversized fabrications that would not fit in a galvanising bath can all be zinc sprayed without issue.
• Controllable thickness: Coating thickness is applied to specification — whether that is 100 microns for general use or 200+ microns for severe marine environments. You get what the engineer specifies, consistently.
• Touch-up and repair: If coating gets damaged during transport or installation, it can be locally re-blasted and re-sprayed. No need to strip and re-do the whole item.

Applications

Zinc arc spraying is specified across a wide range of industries and project types in New Zealand:

• Structural steel: Portal frames, columns, beams, purlins, and connections for commercial and industrial buildings. Particularly useful where steel will be overcoated for aesthetics.
• Bridges and infrastructure: Bridge steelwork, pedestrian bridges, transmission towers, pipeline supports, and other critical infrastructure where long service life is required.
• Marine and coastal: Wharves, jetties, boat lifts, marine hardware, and any steelwork in salt spray zones. New Zealand's coastal environment is aggressive — zinc arc spraying provides the protection these environments demand.
• Commercial buildings: Structural steel for retail, office, and public buildings. Zinc spray plus powder coat gives a durable, attractive finish that holds up for decades.
• Industrial and processing: Equipment frames, platforms, walkways, handrails, tanks, and processing equipment in corrosive industrial environments.
• Water and wastewater: Pipe supports, access platforms, structural steelwork for treatment plants and pump stations.

Zinc Arc Spraying for Steel Fabricators

If you are a steel fabricator, zinc arc spraying solves problems that galvanising creates. Large structural pieces that would need double-dipping or simply would not fit in a bath can be zinc sprayed without any size constraints. There is no waiting on the galvaniser's schedule and no risk of distortion on your carefully fabricated sections.

At Coating Lab, we run the full corrosion protection and finishing process under one roof: abrasive blasting, zinc arc spraying, and powder coating. That means your steel goes from raw fabrication to fully finished in a single facility. Blast, zinc spray, then powder coat — one delivery, one pickup, and no double-handling between separate suppliers.

This integrated approach is particularly valuable for projects where the specification calls for a duplex system (zinc plus topcoat). We control the entire process from surface preparation through to final finish, which means better quality and fewer delays. Talk to us about your next project — we work directly with fabricators across Auckland and can handle structural steel of all sizes.

Our Process

1. Surface Preparation: Abrasive blasting to white metal (SA 2.5 or SA 3) to ensure proper coating adhesion
2. Zinc Arc Spraying: Zinc wire melted and sprayed to the specified thickness using arc spray equipment
3. Sealing: Optional sealer coat applied to fill porosity in the zinc layer
4. Topcoat: Optional powder coat or paint topcoat for aesthetics or additional protection (duplex system)
5. Inspection: Coating thickness and adhesion verified to specification

Specifications and Standards

We work to recognised standards including:

• AS/NZS 2312 — Guide to the protection of structural steel against atmospheric corrosion
• ISO 2063 — Thermal spraying metallic coatings
• Client specifications and engineering requirements

Frequently Asked Questions