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Zincalume

Zincalume is BlueScope's 55% Al / 43.5% Zn / 1.5% Si coated steel for roof and wall cladding. AZ150 and AZ200 grades. The base under Colorbond's painted finish.

By Chalkline. Last updated 14 May 2026. Verified 14 May 2026.

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Zincalume is the BlueScope Steel brand name for aluminium-zinc-coated steel sheet used as roof and wall cladding. The coating is 55% aluminium, 43.5% zinc, 1.5% silicon, hot-dipped onto a steel base. The coating gives Zincalume better corrosion resistance than plain galvanised (zinc-only) steel, particularly in coastal and inland weather environments, while remaining lower cost than stainless or aluminium alternatives.

Standard coating grades per AS 1397:

  • AZ150: 150 g/m² of AZ coating (total, both sides). The volume default for residential roofing in non-marine environments.
  • AZ200: 200 g/m² of AZ coating. Used in moderate-marine zones, more exposed locations, longer-life requirements.

Where Zincalume fits in the product family:

  • Zincalume sheet, unpainted: silvery-grey finish, dulls to a soft matte over years of weather. Used directly where the aesthetic is acceptable (sheds, agricultural, industrial).
  • Colorbond: Zincalume base with a baked-on painted finish in the BlueScope Colorbond colour range. The painted finish provides additional corrosion protection and selectable colour. The Colorbond brand assumes a Zincalume substrate.

Compatibility and corrosion. Zincalume is reactive with several common building metals, and contact with them causes galvanic corrosion that eats through the AZ coating:

  • Copper: most common defect cause. Copper flashing, copper-water-tank overflow, copper antenna brackets on Zincalume roofs all cause progressive holes within years.
  • Lead: similar mechanism; old lead flashings on retrofit roofs are a common issue.
  • Bare (uncoated) steel in direct contact: galvanic action eats both metals, but Zincalume faster.
  • Treated timber (ACQ in particular): the copper actives in ACQ are aggressive on Zincalume. Isolate framing with DPC or use Zincalume-rated fixings.

Compatible materials: Zincalume, Colorbond, aluminium, stainless steel (with care), zinc, galvanised steel.

Coastal exposure. Zincalume corrosion resistance depends on exposure:

  • Very severe marine (within ~100 m of breaking surf, exposed): AZ150 is not warranted; use Colorbond Ultra (AM150 coating) or stainless.
  • Severe marine (~100 m to ~1 km of surf): AZ200 Colorbond is typical.
  • Moderate marine (~1 to 10 km of surf): AZ150 Zincalume or Colorbond is acceptable.
  • Inland: AZ150 is standard.

For builders.

  1. Spec the coating grade with the location. AZ150 default; AZ200 or Colorbond Ultra for marine.
  2. Audit flashings on retrofits. Old copper or lead flashings on a Zincalume reroof must be removed; leaving them in place voids the warranty and causes documented failures.
  3. Isolate from ACQ-treated framing. A layer of DPC between the framing and the Zincalume sheet, or use Zincalume-rated fixings throughout. Letterbox-mounted Zincalume flashings into ACQ-treated outdoor posts is a known failure pattern.

Also known as: Zincalume steel, AZ150 / AZ200 steel, aluminium-zinc coated steel.

Category: Materials / metal roofing / coatings.

See also

Last updated: 2026-05-14. Verified: 2026-05-14.

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