Hot-Dip Galvanizing: Does Thicker Mean Better?
Apr 17, 2026
Introduction
If hot-dip galvanizing is chosen as the surface treatment for steel-structured photovoltaic carports, what is the appropriate zinc coating thickness? And is thicker always better?
Of course, the required coating thickness also depends on the installation location.
Environmental Factors Matter
In coastal areas, the air and humidity are more corrosive to the coating than in other regions.
In areas with good air quality, rainwater causes much less corrosion to the coating.
There are also corresponding standards for coating selection based on regional conditions.
Standard Requirements: GB vs. EN
|
Workpiece Type |
GB/T 13912-2020 (China) |
EN ISO 1461:2022 (Europe) |
|
Cast iron (thickness ≥ 6mm) |
Local thickness: ≥ 70μm |
Average thickness: ≥ 80μm |
|
Cast iron (thickness < 6mm) |
Local thickness: ≥ 60μm |
Average thickness: ≥ 70μm |
Key observation: For average coating thickness, the EN standard is slightly higher than GB. For local thickness (i.e., uniformity), GB is more demanding than EN. Therefore, for products destined for the European market, simply increasing the average thickness requirement will fully satisfy the standard while achieving a more uniform galvanized layer.
What About More Aggressive Environments, Such as Coastal Areas?
Under EN standards, there is no direct thickness requirement. Instead, the classification is based on corrosivity categories and the expected service life of the hot-dip galvanized coating:
|
Corrosivity Category |
Description for Coastal Areas |
Expected Service Life (85μm coating) |
|
C4 (High) |
Coastal areas with moderate salinity. Typically several hundred meters to a few kilometers from the coastline, affected by some marine salt spray. |
Approximately 20 – 40 years |
|
C5 (Very High) |
Coastal areas with high salinity. Very close to the coastline, directly exposed to sea winds and heavy salt spray, such as waterfront facilities and ports. |
Approximately 10 – 20 years |
|
CX (Extreme) |
Extreme marine environments. Primarily for offshore facilities (e.g., offshore platforms, lighthouses), under long-term high salt spray and high humidity conditions. |
Approximately 3 – 10 years |
A Practical Rule of Thumb
In real-world projects, we use a simple rule to distinguish these three zones:
- C4: If you can see the sea while standing on land.
- C5: If you are on land, but seawater could potentially splash onto the steel structure.
- CX: If you are not on land (i.e., offshore).
So, What Thickness Is Recommended?
Based on the above:
- For normal environments, requiring an average coating thickness of ≥ 80μm is sufficient.
- For areas with salt spray concerns (coastal areas), requiring a thickness of ≥ 85μm is the optimal choice.
Is Thicker Always Better for Extreme Environments?
No.
The galvanized coating is a layer that grows on the steel surface through a chemical reaction. If it becomes too thick, the most likely problem is coating rupture - that is, the adhesion of the galvanized layer decreases, leading to flaking and peeling in sheets.
Conclusion
For normal environments, a coating thickness of 80μm or more is adequate. For areas with salt spray concerns, 85μm or more is the optimal choice. Beyond that, thicker does not mean better - it may actually compromise adhesion and long-term performance.
