It seems logical to assume that a thicker galvanized steel coil would last longer. However, under certain conditions, thicker coils may actually rust faster than thinner ones. The key reason lies in how galvanization interacts with steel thickness and environmental exposure.
Uneven Zinc Coating on Thicker Steel
Galvanized steel is coated with a protective layer of zinc to prevent corrosion. But when steel coils are thicker, achieving uniform zinc coverage becomes more difficult during the hot-dip or electro-galvanizing process. Areas with thinner zinc layers become early targets for rust, especially around edges and bends.
Internal Stress and Microcracks
Thicker steel retains more internal stress during manufacturing. When the coil is bent, cut, or formed, this stress can lead to tiny surface cracks that breach the zinc coating. These microcracks expose the steel substrate to moisture and air, accelerating corrosion.
Slower Drying Time Traps Moisture
Thicker galvanized coils used in humid environments or poorly ventilated storage can hold moisture longer between layers. If stored horizontally or tightly wound, water can become trapped, creating a localized humid microclimate. This condition promotes rust even if the coil is technically protected.
Zinc Layer Breakdown in Aggressive Environments
In coastal or industrial zones, airborne salts or chemical pollutants react aggressively with zinc. On thicker coils, once the outer zinc starts degrading, it takes longer for moisture to evaporate due to the bulkiness of the material. The result is prolonged exposure and a faster path to corrosion.
Common Misconceptions About Coil Thickness
Many buyers mistakenly focus only on steel thickness for durability without considering zinc coating weight (measured in g/m²). A thick coil with low zinc coating offers less corrosion protection than a thin coil with a heavy, even zinc layer.
How to Prevent Premature Rust on Thick Coils
To maximize the lifespan of thicker galvanized coils:
Ensure high zinc coating weight (Z275 or higher)
Request quality certification on coating uniformity
Avoid stacking coils in humid or poorly ventilated areas
Use passivation or oiling treatments for added surface protection
Inspect for damage during forming or transport
When Thicker Steel Is Still the Right Choice
Thicker galvanized steel coils are still essential in structural applications where strength and load-bearing are critical. But to prevent early rust, surface treatment and storage must be carefully managed.
Thicker does not always mean stronger against corrosion. Pay attention to coating quality, environmental exposure, and handling to get the most from galvanized steel.