The wire is the bone. The coating is the skin. We explain Hot-Dip Galvanized (Z), Zinc-Aluminum (ZA) and the new premium Zinc-Aluminum-Magnesium (ZM) — and what each one means for your fixed knot fence in Australian and New Zealand conditions.
Our entire range is coated and tested to AS/NZS 4534, the Australian / New Zealand standard for zinc-based coatings on steel wire. The product is then assembled and verified to AS 2423. The only thing that changes between our three options is the chemistry of the coating layer — and that one variable governs everything from corrosion life to knot integrity.
Pure zinc coating, sacrificial protection of the steel core. Class A and Class B coating mass options. The mainstream Australian rural fencing standard for the past 60 years.
Zinc alloyed with 10% aluminium. Approximately 3× the corrosion resistance of Type Z at equivalent coating mass — a ratio established by AS/NZS 4534 test data. The accepted upgrade for coastal Australian and most New Zealand conditions.
Zinc with ~10% aluminium and ~3% magnesium. Confirmed to exceed Zn-Al in corrosion resistance, with self-healing properties at knots and cut edges. Precise service-life multiples are still being established in ongoing field studies. The new international benchmark for premium fixed knot fence.
Same high-tensile steel core. Three very different protective skins. Coating mass shown is per square metre of wire surface (not "double-side" — that's a sheet-steel convention).
Type ZA corrosion resistance ratio (~3× Type Z) is based on AS/NZS 4534 test data and salt-spray testing per AS 2331.3.1 / ISO 9227. Type Z indicative service life (10–15 years) reflects widely cited field experience for inland AU/NZ conditions. Type ZM is confirmed to exceed ZA in corrosion resistance; precise field longevity data is still being established in ongoing studies. Real-world life depends on environment category (ISO 9223), coating class and installation practice.
Standard galvanized fence wire has exactly one defence: zinc dissolves first to shield the steel. Zinc-aluminium-magnesium stacks four independent mechanisms on the same wire — and that's why service life multiplies, rather than just adds.
Zinc sits lower than iron on the galvanic series (−0.76 V vs −0.44 V). At any breach in the coating, Zn corrodes first and the steel stays cathodic — the same mechanism that's protected galvanized fences for 60 years.
Aluminium in the coating reacts with air to form a hard, nanometre-thin Al₂O₃ film. Water, oxygen and chloride ions struggle to penetrate it — so the zinc beneath barely gets consumed. Corrosion rate drops 3–5× vs pure Zn.
Where the coating is scratched or cut, Mg²⁺, Zn²⁺ and Al³⁺ ions combine with OH⁻ to form a stable layered double-hydroxide mineral (hydrotalcite) that re-seals the exposed steel. This is what makes ZM "self-healing".
Cathodic corrosion normally drives local pH to 11–12, which then attacks zinc itself. Mg(OH)₂ buffers the surface around pH 10 — protecting the zinc from this self-loss and giving ZM its standout performance in alkaline ammonia environments (dairy, beef, poultry).
Cross-section of a Zn-Al-Mg coating on steel wire — left: intact coating with all four mechanisms active; right: a knot / cut breach triggers Layer 3 self-healing as Mg²⁺ and Zn²⁺ ions migrate to the wound and form a layered double-hydroxide film over the exposed steel.
| Mechanism | Type Z (HDG) | Type ZA (Zn-Al) | Type ZM (Zn-Al-Mg) |
|---|---|---|---|
| ① Sacrificial anode (Zn) | ✓ | ✓ | ✓ |
| ② Dense Al₂O₃ barrier | ✗ | partial | ✓ |
| ③ Self-healing LDH film (Mg) | ✗ | ✗ | ✓ |
| ④ pH buffer in alkaline environments (Mg) | ✗ | ✗ | ✓ |
| Mechanisms active | 1 / 4 | 2 / 4 | 4 / 4 |
Each additional mechanism multiplies corrosion resistance rather than just adding to it. This is why coating mass alone doesn't tell the full story — ZM's combined mechanisms give it a structural advantage over pure-zinc coatings well beyond what a simple mass comparison would suggest.
The knot is the proudest feature of this fence — and also the spot where the coating works hardest. Three wires meet, get bent through a tight radius, and any micro-crack in the coating exposes bare steel to the weather. This is where the three coatings diverge most.
Type Z fails at the knot first. Cold-forming the knot stretches the zinc layer beyond its elastic limit. Micro-cracks form, water seeps in, and red rust appears at the knot years before it appears on the wire itself.
Type ZA reduces that risk significantly. The denser Al-rich oxide is more crack-tolerant in the knot radius, and 10% aluminium slows the spread of corrosion from any breach point.
Type ZM actively repairs the knot. Where the coating is breached, magnesium combines with zinc and aluminium ions to form a stable layered-hydroxide film that re-seals the bare steel. This same chemistry is what protects cut edges and end-cuts. This self-healing property is widely regarded as a key reason ZM consistently outperforms ZA in real-world service, though precise longevity multiples are still being confirmed by ongoing field studies.
"High tensile" doesn't mean the same number in every market. Australian rural fencing has its own long-standing convention; the international premium spec sits one tier higher. We supply both, on any of the three coatings.
| Wire role | AU standard build (HT line + MT stay) | NZ / international premium (HT line + HT stay) |
|---|---|---|
| Line wire (horizontal) | HT 2.50 mm · 1100–1450 MPa · AS/NZS 4534 | HT 2.50 mm · 1370–1550 MPa · AS/NZS 4534 |
| Stay wire (vertical) | MT 2.50 mm · 750–1000 MPa · AS/NZS 4534 | HT 2.50 mm · 1240–1450 MPa · AS/NZS 4534 |
| Knot wire | Soft / annealed · 350–550 MPa | Soft / annealed · 350–550 MPa |
| Typical use | Mainstream AU rural distributors & merchants | NZ premium deer / dairy / equine; international export |
| Indicative price difference | Baseline | +10–15% per linear metre |
| Best fit | AU mainstream, sheep / beef, long boundaries | Deer / equine, high-impact stock, lifetime-cost projects |
Both builds comply with AS/NZS 4534 (coating) and AS 2423 (fencing product). The "AU standard" configuration is what most Australian distributors and rural merchants spec by default. The "premium" configuration matches the international fixed-knot benchmark used in deer farming, conservation perimeters and high-investment livestock projects.
No part of New Zealand is more than ~130 km from the coast, and NZ is the world leader in dairy and high-density beef on pasture. Your fence sees both chloride spray and alkaline ammonia — two of the most aggressive corrosion drivers known. The right coating choice isn't optional here, it's economic.
Acceptable only for genuinely inland blocks more than 20 km from coast and well away from livestock buildings. Expect to re-strain or replace at the 10–15 year mark.
A safe default for most North and South Island farms. Approximately triples the corrosion resistance of Type Z at a modest cost premium — the improvement ratio established by AS/NZS 4534 test data. Pairs well with treated posts on a longer replacement cycle.
The only coating engineered for both coastal salt and dairy ammonia. Self-healing knots and cut edges mean the fence outlasts the posts you stretch it to. Specify this for any coastal, dairy, deer or conservation project where lifetime cost matters more than upfront cost.
The questions that come up most often when buyers consider switching from Type Z to ZA, or from ZA to the new ZM coating.
See wire gauges, knot spacing, roll lengths and coating options on the product page — or send us your project brief and we'll recommend the right wire grade + coating tier for your site.