News
9 Feb, 2026

Zinc-Al-Mag Vs. Galvanised Steel Top Hats

zam coated tophats

Selecting the correct sub‑framing is vital to ensuring a building’s long‑term durability, structural integrity and code compliance. While galvanised and Zinc-Aluminium-Magnesium (Zn-Al-Mg) coatings are both established corrosion‑protection systems, their performance diverges, particularly in environments with moisture, salt, or airborne pollutants.

Learn more about Zn-Al-Mg coatings

This article breaks down the science, performance and practical differences to help project teams make informed, evidence‑based decisions.

Composition & Manufacturing: How Each Coating Works

 
Category Zinc‑Al‑Mag  Galvanised Coating
Manufacturing Process Continuous hot‑dip into a molten Zn‑Al‑Mg alloy.
Continuous hot‑dip into molten zinc.
Coating Composition
 Zinc–aluminium–magnesium alloy formed as a single, homogeneous layer. Pure zinc coating.
Protection Mechanism
Sacrificial protection + enhanced barrier film created by the Al‑Mg alloy.
Sacrificial zinc protection only.
 
The chemistry of a coating determines how well it performs over decades of exposure. A Zn‑Al‑Mg alloy forms a unified, stable protective layer, allowing the coating to remain effective even when cut, drilled or exposed during installation. In contrast, galvanised coatings rely solely on a zinc layer, which is more easily disrupted and offers less protection once the surface is breached. This fundamental structural difference underpins the durability, edge stability and long‑term performance advantages seen in Vitrafix Zinc‑Al‑Mag Top Hats.

 

Durability & Corrosion Resistance

Category Zinc‑Al‑Mag Coating Galvanised Coating
Corrosion Rate Demonstrates significantly slower corrosion progression, particularly in chloride‑rich, industrial and high‑humidity zones. Performs reliably in mild to moderate conditions but corrodes faster in coastal or pollutant‑exposed environments.
Red Rust Formation Delayed. Dense corrosion film forms rapidly and remains stable over time. Earlier onset in harsh environments, especially at cut edges.
Coastal Performance Highly suited. Shows strong resistance where salt exposure accelerates corrosion. Limited. Zinc alone breaks down more quickly in coastal atmospheres.
Industrial Performance Strong. Handles airborne pollutants and wet‑dry cycling effectively. Moderate. Prone to faster degradation in pollutant‑laden environments.
 
Durability depends on how a coating responds to moisture cycles, salt, pollutants and trapped condensation within facade cavities. The Zn‑Al‑Mg coating forms a dense, stable corrosion layer that slows deterioration across all exposure categories, including those that accelerate corrosion in traditional zinc coatings. This delayed red rust formation and improved resistance at vulnerable points help maintain the facade's structural integrity over its design life.
 

 

Installation, Practicality & Maintenance

Category Zinc‑Al‑Mag Coating Galvanised Coating
Cut‑Edge Protection Excellent. Aluminium and magnesium stabilise corrosion, spreading over exposed edges and limiting undercutting. Moderate. Cut edges are more vulnerable to red rust, especially in salt‑ or pollutant‑rich environments.
Maintenance Requirements Generally lower due to slower corrosion and better edge stability. Higher over time, especially in aggressive climates.
Suitability for Thin Gauges
Performs reliably on thinner steel sections.
Less suitable where thin sections meet demanding exposure.

 

On-site work, such as cutting, drilling, and fastening, inevitably exposes steel to the elements. Vitrafix Zinc‑Al‑Mag Top Hats naturally protect these areas, limiting early corrosion and reducing the need for additional treatments. Galvanised coatings offer less inherent stability once the zinc layer is disrupted, increasing the risk of localised deterioration and maintenance requirements. The consistent behaviour of Zn-Al-Mg coatings at these weak points contributes to a longer‑lasting, more reliable facade assembly.

 

 

Life, Compliance & Value

Category Zinc‑Al‑Mag Coating Galvanised Coating
Service Life (Indicative) Long‑term engineering assessments indicate extended service life, including approximately 27.8 years in C4 zones for Zn-Al-Mg coatings. Service life varies by environment; it is shorter in C3–C5 zones compared to Zinc‑Al‑Mag Top Hats.
Whole‑of‑Life Value Higher value in demanding environments due to extended durability and lower maintenance. Strong in mild environments; less cost‑effective in harsh exposure categories.
Compliance (AS 1397) Classified under ZM coatings (e.g. ZM120, ZM200, ZM275). Meets durability criteria in the standard. Classified under Z coatings (e.g. Z275). Long‑established and widely used.
Long‑term performance and standards compliance depend on a coating’s ability to retain its properties over time. Vitrafix Zinc‑Al‑Mag Top Hats provide a more stable protective layer, supporting extended service life and predictable durability, helping meet AS 1397 requirements with greater certainty. This longer retention of performance reduces whole‑of‑life costs and offers a more reliable pathway to compliance in higher‑risk exposure categories.
 
 

Conclusion

Galvanised steel remains a proven and reliable choice for many applications, supported by decades of successful use. Vitrafix Zinc‑Al‑Mag Top Hats build on that foundation, advancing the protective performance of metallic coatings through its stabilised alloy structure. Its enhanced durability, improved edge protection and longer service life make it particularly suitable for Australian conditions, especially in coastal and industrial environments where corrosion risks are elevated.

Selecting Vitrafix Zinc‑Al‑Mag Top Hats enables facade systems to perform more consistently over time while supporting compliance, durability, and sustainability objectives. When integrated into Fairview’s complete wall systems, it contributes to a robust, fully compliant solution that delivers long‑term value and confidence.

Learn more about Vitrafix Zinc-Al-Mag Top Hats