What is the minimum zinc coating required for heavy structural steel thicker than 5mm?

610 g/m² (equivalent to approximately 85 microns) as per Table 1.

How is the mass of the zinc coating checked on site?

Typically using a magnetic thickness gauge for non-destructive testing, or chemically via the mass determination method specified in IS 6745.

How is coating adhesion tested?

By the pivoted hammer test as per IS 2629, ensuring the coating does not flake or peel off.

IS 4736

: 2003

Hot-Dip Galvanized Coatings on Structural Steel and Other Allied Products - Specification

CurrentFrequently UsedSpecificationMaterials Science · Aluminium and Non-Ferrous Metals

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This standard covers the specification for hot-dip galvanized coatings applied to structural steel shapes, plates, and bars to provide corrosion protection. It details the required zinc coating mass, thickness, adhesion, and appearance criteria based on the thickness of the base steel.

Specifies the general requirements for hot-dip galvanized coatings applied to fabricated structural steel and other products.

Quick Reference Values

Min zinc coating mass (steel thickness > 5 mm)610 g/m²

Min zinc coating mass (steel thickness 2 mm to < 5 mm)460 g/m²

Min zinc coating mass (steel thickness 1.2 mm to < 2 mm)340 g/m²

Equivalent thickness for 610 g/m² coating85 microns

Equivalent thickness for 460 g/m² coating65 microns

Purity of zinc required (as per IS 209)98.5%

Practical Notes

Surface preparation is critical; ensure steel is properly pickled and free from mill scale, rust, and grease before galvanizing to avoid bare patches.

Hot-dip galvanizing involves immersing steel in a zinc bath at around 450°C, which can cause distortion or warping in thin or asymmetrical structural sections.

This standard does not apply to threaded fasteners (nuts, bolts), which are covered under IS 1367 (Part 13).