Steel Finishes & Corrosion Protection QLD | NCC 2022
The right finish for structural steel comes down to one question: how much moisture and salt will the steel be exposed to over its life. In Queensland that matters more than almost anywhere in the country, because so much of South East Queensland sits close to breaking surf or sheltered bays, where salt air drives corrosion hard. Under NCC 2022, the coating on a steel beam is matched to its corrosivity zone and where it sits in the build. This guide explains how that works, and how Network Steel matches the finish to the exposure so your steel lasts and your project passes sign-off.
What changed under NCC 2022?
The corrosion protection rules for structural steel in homes were updated. Clause 6.3.9 of the ABCB Housing Provisions Standard replaced the old Clause 3.4.4.4, with more detailed corrosion protection tables and more options. The environmental categories now align with AS 4312, the standard that maps atmospheric corrosivity zones across Australia, and the code sets a minimum durability design life of 15 years. The changes apply to projects submitted to council or a certifier for construction approval after 1 May 2024.
What corrosivity zone is my build in?
Your corrosivity zone depends on how close the site is to the coast or a sheltered bay. The categories run from C1 to C5-M, and the closer you are to breaking surf, the more aggressive the environment.
| Corrosivity category | Typical location |
|---|---|
| C1 (Very Low) | Dry indoors |
| C2 (Low) | Remote inland, or more than 1km from a sheltered bay |
| C3 (Medium) | More than 1km from breaking surf, or more than 50m from a sheltered bay |
| C4 (High) | More than 200m from breaking surf, or within 50m of a sheltered bay |
| C5-M (Marine, Very High) | 100m to 200m inland from breaking surf, or within 100m of breaking surf |
A lot of SEQ falls into C4 and C5-M. A bayside build at Cleveland or Raby Bay, or a beachfront project on the Sunshine Coast or Gold Coast, sits in the most demanding zones, which is exactly where the coating choice matters most.
Does internal steel need the same protection as external steel?
Two things decide the coating: whether the steel is internal or external, and whether it is in contact with masonry. Once a building is closed in, genuinely internal steel sits in a low-exposure environment. But steel does not start out internal. On site it is often exposed to the weather and salt air for weeks before the house is closed in, and in higher corrosivity zones that exposure alone is enough to justify galvanising, even for steel that will end up inside. That is why Network Steel takes a conservative approach: internal steel gets the compliant coating in the lower zones, and is hot dip galvanised in the high and very high zones (C4 and C5-M).
Galvanised or painted? Network Steel's coating approach
Here is how the coating is matched to the application under NCC 2022. HDG is hot dip galvanising at 600 g/m². The most exposed zones add an epoxy topcoat over the galvanising for extra protection. Each corrosivity category also carries a durability rating, from R1 and R2 at the low end up to R4 for the high and very high zones.
| Application | C2 (Low) | C3 (Medium) | C4 (High) | C5-M (Very High) |
|---|---|---|---|---|
| Internal or concealed, not in contact with masonry | Compliant coating | Compliant coating | HDG 600 | HDG 600 |
| External or exposed, not in contact with masonry | HDG 600 | HDG 600 | HDG 600 + epoxy | HDG 600 + epoxy |
| Internal or concealed, in contact with masonry | Compliant coating | HDG 600 | HDG 600 | HDG 600 |
| External or exposed, in contact with masonry | HDG 600 | HDG 600 | HDG 600 + epoxy | HDG 600 + epoxy |
Posts can also use a pre-galvanised (Duragal) option in place of the compliant coating in the lower zones.
Why does Network Steel galvanise internal steel on coastal jobs?
Because "internal" steel is not internal on day one. On coastal and marine sites, steel often sits exposed on site for a period before the building is closed in and it is deemed internal. For those jobs, Network Steel takes the more conservative path and galvanises, so the steel is protected during the exposed phase and there are no corrosion surprises later. On a beachfront or bayside build, that is cheap insurance against a callback.
The finishes in practice
| Finish | Best suited to | What it delivers |
|---|---|---|
| Compliant coating system | Internal and lower-exposure steel | 25+ years to first maintenance, documented for certifiers |
| Hot dip galvanised (HDG 600) | External steel, steel in contact with masonry, higher corrosivity zones | Durable zinc coating for exposed and coastal conditions |
| HDG plus epoxy topcoat | The most aggressive C4 and C5-M exposed marine zones | Maximum corrosion protection close to breaking surf |
FAQ
How do I know my project's corrosion category?
Your engineer assigns the corrosivity category based on the site's distance from breaking surf and sheltered bays, and records it in the engineering documentation.
What counts as internal versus external steel?
Internal or concealed steel is generally above the damp proof course and enclosed within the building once construction is complete. External or exposed steel faces the weather. The two are coated differently because they face very different exposure.
Is a standard primer enough under NCC 2022?
No. A light zinc phosphate primer of around 15 microns is not compliant with the updated code and can need first maintenance in under five years. Network Steel's compliant coating system is built to exceed the 15-year minimum durability design life, delivering 25 or more years to first maintenance.
Should coastal steel always be galvanised?
Exposed and marine-zone steel is hot dip galvanised, and the most aggressive C5-M conditions add an epoxy topcoat. In the high and very high corrosivity zones, Network Steel also galvanises steel destined to be internal, because it sits exposed on site before the building is closed in.
Does the compliant coating add to lead time?
No. The compliant coating system does not add lead time compared with the previous primer.
Can Network Steel certify the coating system?
Yes. Network Steel can provide certification on the compliant coating system so it is documented for your certifier.
Not sure which finish your project needs? Speak to our team, or book a corrosion consult with our Product Technical Manager, Brooke Madeley.
