Know your Microns –
Galvanized Steel Coating Thickness
It is remarkable to think that a coating, just thicker than a sheet of A4 paper, can protect a steel structure for the better part of one hundred years.
It’s remarkable to consider that a coating just thicker than a sheet of A4 paper can protect a steel structure for nearly a century. But that’s the reality of hot dip galvanizing—where a microscopic layer of zinc delivers robust, reliable corrosion resistance, even in the harshest environments.
What is the thickness of a galvanized coating?
When it comes to the specification of hot dip galvanizing, most contractors know that to be standards compliant, for example 7mm steel requires an average coating thickness of ‘85 microns’.
It refers to the standard average coating thickness required on steel greater than 6mm to meet EN ISO 1461—the benchmark for hot dip galvanizing in construction.
But how does that microscopic coating translate into performance? And what does ‘85 microns’, actually look like?
- A human hair is about 50 microns in diameter.
- The naked eye struggles to perceive objects smaller than 40 microns.
- Cling film is around 10–12 microns thick.
- A typical bacterium is 1–10 microns long.
Hot Dip Galvanizing Thickness and Steel Thickness
More Than Surface Deep: How Galvanized Coatings Work
Coating Thickness by Steel Size
But thickness isn’t the only factor. Steel chemistry—particularly its silicon content—also affects reactivity during galvanizing. Higher silicon levels increase the reaction between steel and zinc, leading to a thicker coating. Understanding this interaction helps designers and fabricators anticipate coating outcomes more accurately.
Weathering the Elements: Predictable, Long-Term Protection
The corrosion rate of a galvanized coating is generally linear.
Galvanized coatings weather over time, but they do so in a predictable, linear fashion. In drier, inland UK locations, corrosion rates are less than 1 micron per year. This consistency offers a major advantage over other protective coatings, which may fail suddenly or unpredictably.
And thanks to improved air quality—particularly lower sulphur dioxide levels—galvanized coatings in the UK and Ireland are performing better than ever. The legacy of clean air regulations is longer-lasting steel.
Why Knowing Your Microns Matters
Specifiers and engineers who understand coating thickness can make smarter, more sustainable decisions. A few microns can translate to decades of extra performance—and significant savings in maintenance, materials, and environmental impact.
In the end, galvanizing is proof that in the world of infrastructure, size isn’t everything.
A microscopic coating can make a monumental difference.
85 microns. One decision. A century of protection.
Know your microns—and design for the future.
Moreover, in the UK and Ireland, as sulphur dioxide levels have fallen, corrosion protection has been extended. It does indeed pay to know your microns.
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