The secret weapon against corrosion: zinc-rich paint technology

Source: Supplied. Simon Norton, director of the International Zinc Association (IZA) Africa.

As South Africa’s infrastructure faces harsh weather, coastal exposure and ageing assets, these advanced coatings are increasingly essential to extend structural lifespan, reduce maintenance costs, and strengthen long-term durability across building and infrastructure projects.

Zinc-rich paints are used when it is not possible to hot-dip galvanise steel, or during maintenance and upgrade projects where a high-performance anti-corrosion coating is required beneath the topcoat. Corrosion remains one of the most persistent threats to steel, particularly in coastal regions, industrial zones and high-humidity environments.

“Corrosion can significantly weaken steel over time, and without proper protection it places buildings, bridges and critical infrastructure at risk,” says Simon Norton, director of IZA Africa.

Sacrificial corrosion protection

Zinc-rich paints provide powerful sacrificial protection. As zinc is more reactive than iron, it corrodes first, safeguarding the underlying steel and preventing rust formation. Zinc-rich paints contain high concentrations of zinc dust or flake, typically between 50% and 80%, suspended in a resin binder.

This formulation not only allows the zinc to act sacrificially but also creates a barrier effect. As zinc particles react with moisture and oxygen, they form zinc oxide, which further blocks ingress of corrosive agents from reaching the underlying steel.

“These coatings deliver exceptional corrosion resistance,” explains Norton. “They are also versatile, with excellent adhesion to bare steel, galvanised surfaces and even previously coated steel, provided correct surface preparation is undertaken.”

Zinc-rich paints are well suited to a wide range of applications across building construction, including primary and secondary steelwork, and refurbishment projects. They are also widely used in maintenance and repair, particularly for touching up damaged galvanised coatings or addressing early-stage corrosion on ungalvanised steel structures.

Self-healing protection benefits

In addition to sacrificial and barrier protection, some zinc-rich paints offer self-healing properties.

When minor scratches expose the steel, the surrounding zinc reacts to form a protective zinc oxide layer that slows further corrosion. Norton adds that these paints are also resistant to cathodic disbonding, a problem associated with some traditional anti-corrosion coatings.

Choosing the correct zinc-rich paint requires consideration of zinc content, binder type, surface-preparation requirements and compliance with environmental regulations, including limits on volatile organic compounds. Proper application is equally important and typically involves two to three coats applied within the manufacturer’s specified environmental parameters.

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“High quality zinc coatings are only as effective as the preparation that precedes them,” notes Norton. “Steel surfaces must be thoroughly cleaned and treated to ensure proper adhesion. By following best practice, architects, engineers and contractors can significantly extend the lifespan of steel structures.”

IZA Africa encourages construction professionals to call the IZA Africa when selecting coatings for demanding environments and reminds the industry of the growing importance of durable materials within sustainable building frameworks.

“Zinc-rich paints are a vital component in protecting steel and ensuring that structures remain safe and sound for decades,” concludes Norton. “Understanding how these products work and how to apply them correctly is essential for anyone involved in the built environment.”