Galvanized vs PVC vs Galfan: Which Wire Coating Actually Lasts
Compare hot-dip galvanized, Galfan and PVC coated wire by service life, not price: ISO 9223 corrosion rates, coating-mass-to-years formula, cost per year of service, and five goods-in tests.
The only question that matters
Every wire coating argument comes down to one number: how many years until the steel is exposed. Not "which is best" — a 275 g/m² galvanized wire beats a 0.3 mm PVC coating over 60 g/m² zinc, and a 0.5 mm PVC coating over 240 g/m² zinc beats both. The coating system is a stack, and the stack is only as good as its weakest layer.
Here is how the three commercial options actually behave, and how to calculate the life you are buying.
How zinc protects steel
Zinc protects in two ways, and both matter:
As a barrier. The zinc layer is physically between the steel and the atmosphere. At 240 g/m², the coating is roughly 34 µm thick over the wire surface.
As a sacrificial anode. Zinc is less noble than steel, so at a scratch or a cut end, the zinc around the exposed steel corrodes preferentially and protects it. This is why a galvanized wire survives a scratch that would start rust on a painted one.
That second mechanism is the whole reason hot-dip galvanizing is specified for wire mesh and paint is not. A cut end on hot-dipped wire has 10–20 mm of sacrificial protection around it. A cut end on painted wire has a rust initiation site.
Hot-dip versus electro-galvanized: not the same product
| Electro-galvanized | Hot-dip galvanized | |
|---|---|---|
| Coating mass | 10–40 g/m² | 200–400 g/m² |
| Thickness | 1.5–6 µm | 28–56 µm |
| Bond | Mechanical, weak | Metallurgical alloy layer |
| Protection at cut ends | Almost none | 10–20 mm |
| Life, C3 inland | 4–8 years | 25–40 years |
| Relative cost | 0.85× | 1.00× |
Electro-galvanized wire is a legitimate product for indoor applications — mesh guards, shelving, filtration. It is not a legitimate product for outdoor fencing, gabion or slope protection, and the price difference is only about 15%.
The confusion arises because both are called "galvanized" and both look silver when new. Electro-galvanized is bright and uniform; hot-dip has a slightly rougher, more crystalline surface and often a visible spangle. On woven mesh, the give-away is the cut ends: hot-dip shows a zinc-rich edge, electro-galvanized shows bare steel within a season.
Galfan: what 5% aluminium actually buys you
Galfan is a zinc alloy with 5% aluminium and a trace of mischmetal (rare-earth elements). The aluminium changes the corrosion product that forms on the surface: instead of the bulky, semi-adherent zinc oxide, it forms a thinner, more protective layer that resists chloride attack.
The practical result, in the same coating mass:
| Environment | Hot-dip zinc life | Galfan life | Ratio |
|---|---|---|---|
| Rural / C2 | 30–40 years | 45–60 years | 1.5× |
| Urban / C3 | 25–40 years | 40–55 years | 1.6× |
| Industrial / C4 | 12–20 years | 22–35 years | 1.8× |
| Coastal / C4–C5 | 10–18 years | 18–30 years | 1.7× |
The improvement is largest exactly where it is needed most — in chloride and sulphur environments. Galfan costs about 12–18% more than hot-dip zinc for the same coating mass, which is one of the best ratios in the industry: a 15% premium for 60–80% more life.
The catch is availability. Galfan requires a dedicated continuous galvanizing line, and not every Chinese mesh plant has one. If a supplier offers "Galfan" at the same price as hot-dip, ask for the coating composition certificate — Zn-5%Al has a specific metallurgical signature, and pure zinc sold as Galfan is not uncommon.
PVC: what the plastic does and does not do
A PVC coating is a physical barrier, 0.4–0.6 mm thick, bonded over a galvanized core. It provides:
- A colour (green, black, grey, and RAL shades)
- Abrasion resistance, useful on gabion facing stone and on fences subject to vehicle contact
- A second barrier against chloride in coastal and marine environments
- A smoother surface that sheds water and dirt
It does not provide:
- Any protection at all if the core is thin. PVC over electro-galvanized wire is worse than plain hot-dip, because the plastic traps moisture at every scratch and prevents the zinc from passivating.
- UV permanence in bright colours. Green and black are the most stable formulations; reds and yellows fade measurably in 5–8 years in high-UV climates.
- Repairability. A gouged PVC coating cannot be repaired in the field to the original performance. Hot-dip galvanizing can be patch-repaired with zinc-rich paint.
The specification that matters is the core: 240 g/m² hot-dip zinc underneath, PVC thickness 0.4 mm standard and 0.5–0.6 mm marine grade, adhesion tested to EN ISO 2409 or ASTM D3359.
Corrosion rate by environment
The ISO 9223 corrosivity categories give the zinc loss rate, which is what lets you convert coating mass into years:
| Category | Environment | Zinc loss (µm/year) | Zinc loss (g/m²/year) |
|---|---|---|---|
| C1 | Heated, dry interior | < 0.1 | < 0.7 |
| C2 | Rural, low pollution | 0.1–0.7 | 0.7–5 |
| C3 | Urban, moderate SO₂ | 0.7–2.1 | 5–15 |
| C4 | Industrial, coastal | 2.1–4.2 | 15–30 |
| C5 | Severe industrial, marine | 4.2–8.4 | 30–60 |
| CX | Offshore, tropical marine | > 8.4 | > 60 |
The conversion: zinc density is 7.14 g/cm³, so 1 µm of coating = 7.14 g/m².
The life calculation
Years = coating mass (g/m²) ÷ annual loss (g/m²/year)
A 240 g/m² coating in a C3 urban environment losing 10 g/m²/year gives 24 years. The same coating in C5 coastal conditions losing 45 g/m²/year gives 5.3 years.
This is why the same product is sold with claims ranging from "5 years" to "50 years" — both can be honest, in different environments. The number that matters is the coating mass, and it is the number most often missing from a quotation.
One nuance: the calculation is conservative because zinc loss slows as the coating thins and the corrosion products build up. Real service life in C3 typically runs 20–40% above the straight-line figure. Do not count on the bonus; size for the straight line.
Cost per year of service
| System | Coating mass | Cost index | Life, C3 | Cost per year |
|---|---|---|---|---|
| Electro-galvanized | 30 g/m² | 85 | 5 years | 17.0 |
| Hot-dip standard | 240 g/m² | 100 | 25 years | 4.0 |
| Hot-dip heavy | 275 g/m² | 108 | 30 years | 3.6 |
| Galfan | 255 g/m² | 115 | 40 years | 2.9 |
| PVC over 240 g/m² | 240 g/m² + 0.4 mm | 135 | 40 years | 3.4 |
| PVC over 240 g/m², marine | 240 g/m² + 0.6 mm | 145 | 50 years | 2.9 |
Read that last column, not the third. Electro-galvanized is 15% cheaper to buy and four times more expensive per year of service. This is the single most useful table in any wire specification argument.
Writing the specification so it can be enforced
Four standards carry almost all the enforcement weight:
- ISO 1461 — hot-dip galvanized coatings on fabricated steel. Defines minimum coating mass by thickness.
- ASTM A975 — zinc-coated and PVC-coated double-twist hexagonal mesh (gabion). Defines coating classes from 40 to 290 g/m².
- EN 10223-3 — European standard for hexagonal steel wire mesh for engineering purposes.
- ASTM A641 — zinc-coated carbon steel wire, the base material standard.
Specify coating mass in g/m² with the test method, not a class letter. "ASTM A975 Class 3" means 240 g/m² only if both parties agree on the class table, and in practice they often do not.
Five tests you can run at goods-in
You do not need a laboratory to catch most coating problems:
- Weigh-count. Cut a one-metre length of wire, weigh it, strip the zinc in hydrochloric acid (inhibited), weigh again. The difference divided by surface area is the coating mass. Crude, but it settles arguments.
- Micrometer. Measure wire diameter before and after stripping. A 240 g/m² coating adds about 34 µm to the diameter — if stripping changes the diameter by 6 µm, you have been sold electro-galvanized.
- Copper sulphate dip. Immerse a sample in copper sulphate solution for one minute. A hot-dip coating resists four dips; a thin coating shows copper plating on the first.
- Bend test. Bend a wire 180° around its own diameter. Hot-dip coating should crack but not flake off. Flaking means a brittle, over-thick or poorly bonded coating.
- Salt spray report. Ask for ASTM B117 results — but read the hours against the coating mass. 500 hours on a 40 g/m² coating is less impressive than 1,000 hours on 240 g/m², and suppliers quote hours without mass.
For gabion and slope protection, our coating options run from 240 g/m² standard hot-dip through 275 g/m² heavy, Galfan, and PVC over 240 g/m². Every shipment ships with a coating mass certificate per ASTM A975 — because the number on the certificate is the only thing that survives 20 years in the ground.
Frequently asked questions
Which coating lasts longest?
PVC over 240 g/m² hot-dip zinc, at 40–50 years in most environments. If PVC is not acceptable for aesthetic or abrasion reasons, Galfan at 40 years is the next best.
Is Galfan worth the extra cost?
In coastal, industrial and high-chloride environments, yes — a 15% premium for 60–80% more service life. In a dry rural environment the advantage narrows and standard hot-dip is the rational choice.
Can I use electro-galvanized mesh outdoors if I paint it?
You can, but you are relying entirely on the paint, and paint on wire mesh fails at every cut end and every flex point. For anything expected to last more than 8 years outdoors, hot-dip is the cheaper answer over the life of the installation.
How do I know the zinc mass without a lab?
Ask for the mill certificate and check it against a micrometer reading before and after stripping one sample. If the coating is under 20 µm, it is not 240 g/m², whatever the paperwork says.
Does thicker zinc always mean longer life?
Up to about 300 g/m², yes, roughly linearly. Beyond that the coating becomes brittle and can flake during weaving or bending, which creates bare spots that corrode faster than a thinner, well-bonded coating. 240–275 g/m² is the practical optimum for woven mesh.
