AS/NZS 4680: hot-dip galvanised coatings on fabricated ferrous articles
AS/NZS 4680:2025 sets the coating thickness, mass, and quality requirements for hot-dip galvanised coatings on fabricated ferrous articles in Australia and NZ.
Ask Chalkline about this →AS/NZS 4680:2025, Hot-dip galvanized coatings on fabricated iron and steel articles, is the joint Australian and New Zealand standard for batch hot-dip galvanising of fabricated steel components. It specifies the minimum coating mass, coating thickness, and test methods that every compliant HDG coating must meet (verified 2026-05-16, Standards Australia Store, AS/NZS 4680:2025).
The 2025 edition supersedes AS/NZS 4680:2006 and was published on 27 June 2025 (verified 2026-05-16, Intertek Inform, AS/NZS 4680:2025).
Scope
The standard covers HDG coatings applied by dipping fully-fabricated steel articles in a molten zinc bath:
- Structural steel (beams, columns, brackets)
- Steel sheet fabrications, assembled steel products
- Tubular fabrications, fabricated wire work
- Steel forgings, stampings, castings, nails, and small components
The article is fabricated first, then galvanised. The whole component, including the inside of welds and the hidden faces of plates, is coated in one bath.
What AS/NZS 4680 does not cover:
- Threaded fasteners: covered by AS/NZS 1214 (bolts, screws, nuts).
- Continuous galvanised hollow sections (pre-galvanised RHS, SHS): covered by AS/NZS 4792.
- Pre-galvanised sheet (Z600, Z350 zinc-coated steel sheet): covered by AS 1397.
Specifying “HDG to AS/NZS 4680” on an item from these other categories is a category error; check which standard actually applies.
Coating designations
AS/NZS 4680 ties coating thickness to the base steel thickness (thicker steel pulls a thicker coating out of the zinc bath). The standard designations (verified 2026-05-16, Galvanisers Association advisory note):
| Article (steel) thickness | Designation | Min coating mass | Min coating thickness |
|---|---|---|---|
| Over 1.5 mm to 3.0 mm | HDG390 | 390 g/m² | 55 µm |
| Over 3.0 mm to 6.0 mm | HDG500 | 500 g/m² | 70 µm |
| Over 6.0 mm | HDG600 | 600 g/m² | 85 µm |
The “HDG” prefix plus the coating mass (g/m²) is the standard shorthand specifiers use. “HDG600” means a coating averaging at least 600 g/m² (≈85 µm) on a single measured area.
Coatings thicker than 85 µm are not specified directly in AS/NZS 4680, but the general provisions still apply. For marine or industrial-corrosive environments, specify a thicker coating (e.g. “HDG900, 130 µm minimum”) as a project requirement on the drawings and confirm the galvaniser can achieve it on the article geometry.
Where AS/NZS 4680 shows up on a residential site
- Structural steel beams and columns: the engineer’s spec usually reads “HDG to AS/NZS 4680, 600 g/m² minimum” for any external or unprotected internal steel.
- Brackets and hold-down plates: tie-down brackets, post bases, and joist hangers in HDG finish must comply.
- Reinforcement and ferrules: site-fabricated cast-in items where corrosion protection matters.
- Wall ties and lintels: in some product categories the manufacturer specifies HDG per AS/NZS 4680 on the product datasheet.
What you check on delivery
- Coating designation matches the spec (HDG390 / HDG500 / HDG600).
- Surface is fully coated: no bare patches, no large dross inclusions, no excessive runs. Small touch-up paint applications are permitted within the standard’s tolerances.
- Threaded items not covered: AS/NZS 4680 doesn’t apply to bolts or coach screws. Those are AS/NZS 1214 (and the spinning operation after galvanising restores the thread fit, which AS/NZS 4680 does not address).
- Test certificate for major structural items: galvanisers can supply a coating mass test certificate per AS/NZS 4680 test methods (magnetic thickness gauge or strip-and-weigh).
Common builder issues
- Substitution with paint-grade or zinc-rich paint: a “galvanised look” paint is not AS/NZS 4680 compliant and won’t deliver the design service life. The drawings call HDG for a reason: typically 25-50 years to first maintenance on coastal or external exposure.
- Cut or drilled on site after galvanising: any cut, weld, or drill hole exposes bare steel. The standard allows site touch-up with zinc-rich paint at limited percentages of total coated area; over that limit, the article must be re-dipped.
- Wrong standard cited: HDG specified for a bolt should reference AS/NZS 1214, not AS/NZS 4680. HDG specified for an RHS section that came pre-galvanised may need AS/NZS 4792.
- HDG class 10.9 or 12.9 bolts: not permitted under AS/NZS 1214 due to hydrogen embrittlement risk. See AS 4291.1: property-class system for the underlying property-class detail.
References
- AS/NZS 4680:2025, Hot-dip galvanized coatings on fabricated iron and steel articles (verified 2026-05-16)
- Galvanisers Association of Australia, Advisory Note 28: Hot-dip galvanizing Standards (verified 2026-05-16)
Related
See also
Last updated: 2026-05-16. Verified: 2026-05-16.