Transmission towers sit outdoors, under constant weather, carrying some of the country’s most critical infrastructure. While the galvanising does a great job protecting the steel, it does not last forever. Left untreated, corrosion eventually arrives and it doesn’t just affect appearance, it steadily weakens the steel structure itself. Proper preparation and applying a protective coating system is how that process gets stopped before it becomes a structural problem.
CAKE Group is currently undertaking a tower recoating project for Transpower on the Huntly-Otahuhu A-line, working through a run of 10 towers along the corridor. Recoat projects are when we are painting the tower for a second time as the coating system eventually breaks down over time. This keeps the galvanising and underlying steel protected.
What does transmission tower painting involve?
Tower painting isn’t a single top-up coat. It’s a staged process, because different parts of the same tower can be in very different condition. Some steel may only need light attention, while corroded sections need to be brought back to bare metal, meeting exact preparation standards before anything gets painted.
The process on this project follows these stages:
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Stage 01
Spot preparation
Corroded or damaged areas are prepared using either wet abrasive blasting or hand mechanical preparation, depending on the sensitivity of the site and surrounding area.
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Stage 02
Spot zinc coat
A zinc-rich coating is applied to the prepared steel, providing the primary layer of corrosion protection, replacing the job of the galvanising layer.
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Stage 03
Spot undercoat
An undercoat is applied over the zinc to build the system before the final layer.
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Stage 04
Full top coat
The tower receives a full top coat across the structure, tying the spot-repaired areas in with the rest of the tower.
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Stage 05
Anti-climb reinstatement
Before handover, anti-climb protection wires are reinstated so the tower is returned to Transpower fully compliant and secure.
This spot-and-full-coat approach means towers can be brought back to standard without unnecessary full strip-backs on sections that don’t need it, but it also means the crew has to make accurate calls, tower by tower, about where full preparation is actually required.
Why this kind of work is treated as high-risk
Painting on live transmission infrastructure isn’t a standard commercial coatings job. The towers are energised and the lines are usually on and “live” when working. This is always at height and spread across varied terrain, and any work has to be planned and executed without compromising the line’s operation or the safety of the people carrying it out.
Because of this, CAKE works closely with Transpower’s health and safety coordinators and project managers throughout delivery, rather than treating H&S sign-off as a separate, later step. That collaboration runs alongside the technical process, not after it.
Coordinating work across regions
Projects like this aren’t delivered from one site. With towers spread across different parts of the whole country, keeping the work consistent means maintaining a defined process that travels with the crew from tower to tower, and holding monthly meetings with Transpower to stay aligned on progress, access, and any site-specific issues as they come up.
This is the less visible side of tower work, the coordination that keeps a multi-tower, multi-region project moving as one job rather than ten disconnected ones.
Corrosion protection as ongoing infrastructure maintenance
Corrosion is a genuinely global cost, not just a New Zealand one. The NACE International IMPACT study puts the global cost of corrosion at roughly 3.4% of global GDP.
Structures exposed to weather, like transmission towers, are exactly the kind of asset that number is measuring. Protective coating work like this is what keeps that cost from compounding on infrastructure that can’t afford unplanned downtime.
FAQs
What is tower painting?
Tower painting is the process of preparing and applying protective coating systems to steel transmission towers to slow the progress of corrosion and to extend the working life of the structure.
Why can’t a tower just get a fresh top coat without prep?
Coating over corrosion doesn’t stop it. It seals moisture and contamination in and can create an even worse outcome. Corroded sections need to be properly prepared (via wet abrasive blasting or mechanical preparation) down to a suitable surface before any new coating system will hold.
Is transmission tower painting dangerous work?
It’s classed as high-risk work due to the height, live infrastructure, and site conditions involved, which is why it’s carried out in direct coordination with the asset owner’s health and safety team throughout, not just at sign-off.
How is a multi-tower project like this managed?
Through a consistent, active management process applied tower by tower, and regular alignment meetings with the client and other stakeholders, such as landowners, to keep work coordinated across public and private property.