Tool
Fence coating calculator: what grade suits my site?
The SIMO Securon fence coating calculator places your site in a corrosion category under ISO 9223, from its distance to the sea, the air around it and the weather. It then works out the least coating, in GSM, of galvanised zinc, Zn-Al 95/5 or Zn-Al 90/10 for the life you need, and recommends the grade.
- Tell us about your land.
- See the fence it needs, with posts and rolls worked out.
- Get your price on WhatsApp from the SIMO Securon team.
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6Your fence coating
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We check the category from your PIN code, then recommend the fence, the coating and the posts, and send the price.
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What happens next
- An engineer checks your site from the PIN code and calls or WhatsApps you within 2 to 3 working hours.
- We recommend the fence, the coating and the posts, and send the price.
- For a site near the sea or chemicals, we arrange a site review.
How the fence coating calculator works
A metallic coating protects steel wire by being used up instead of the steel. How long it lasts is simple arithmetic: the coating mass divided by how fast the site uses it up. The calculator does that sum in four steps.
- It places your site in a corrosivity category under ISO 9223. The standard describes typical environments for each category; the calculator takes the most severe of your three answers (the sea, the air around the site and the weather). Manure, fertiliser or standing water at the fence line moves the site one category up, because the standard’s categories describe the open air, not the ground the fence stands in.
- It takes the zinc lost each year at the worst end of that category, from the standard’s first-year corrosion rates: in C3, 5 to 15 g/m² of zinc a year. Designing to the worst end means the coating lasts even where your site is harsher than average for its category.
- It multiplies by the years you need, and divides by how long each coating lasts against zinc. Galvanised zinc counts once. Zn-Al 95/5 counts twice: field studies reported by GalvInfo found it at least twice as resistant outdoors as galvanised at the same coating mass, and EN 10223-6 treats it as lasting like a heavier zinc coating. Zn-Al 90/10 counts 2.5 times: that is SIMO Securon’s design basis for its own coating, the figure at which its grades reach their rated lives at the worst end of C3. No standard gives a figure for 90/10, so treat it as SIMO’s.
- It recommends a grade, or a site review. A SIMO Securon grade is recommended only when its rated life covers your years and its own metallic coating meets the minimum. From C4 up, it recommends a polymer coating over the metal and a site review, because the grades’ rated lives apply up to C3.
If you are not sure how long the fence must last, choose “Not sure”. Four questions (how long you will use the site, when you would replace the fence, what you can spend now, and what matters more) give a figure, and the calculator says how it got there.
Corrosivity categories in India under ISO 9223
ISO 9223 sets six categories by how fast standard samples of zinc, steel, copper and aluminium corrode in their first year outdoors. The table gives the zinc figure for each, with the kind of site in India that usually falls in it. A measured classification, from samples exposed at the site for a year, always beats an estimate.
| Category | Corrosivity | Typical sites in India | Zinc lost a year (g/m²) |
|---|---|---|---|
| C1 | Very low | Dry, heated interiors. Rare for a fence in India. | up to 0.7 |
| C2 | Low | Dry or semi-arid inland areas with clean air. | 0.7 to 5 |
| C3 | Medium | Most of inland India: farms, villages, towns and light industry under a normal monsoon, and sites 5 to 20 km from the sea. | 5 to 15 |
| C4 | High | Within about 5 km of the sea, or within 1 km of heavy industry. | 15 to 30 |
| C5 | Very high | Within about 1 km of the sea, a creek or a salt pan. Inside a chemical or process plant, which ISO 9223 does not cover, the calculator assumes at least C5. | 30 to 60 |
| CX | Extreme | The shoreline, where sea spray reaches the fence. | 60 to 180 |
The least coating for a 20-year fence, by category
The same sum for a fence that must last 20 years, designed to the worst end of each category. For 10 years, halve the figures; for 35, multiply by 1.75 and round up.
| Category | Galvanised (zinc) | Zn-Al 95/5 | Zn-Al 90/10 |
|---|---|---|---|
| C2 (low) | 100 | 50 | 40 |
| C3 (medium) | 300* | 150 | 120 |
| C4 (high) | 600* | 300* | 240 |
| C5 (very high) | 1,200* | 600* | 480* |
| CX (extreme) | 3,600* | 1,800* | 1,440* |
* More than fence wire normally carries: IS 4826 goes up to 290 GSM, on 4 to 5 mm wire. Add a polymer coating instead.
Two things stand out. Galvanised zinc alone cannot give 20 years at the worst end of C3 on fence wire, and from C4 up even Zn-Al would have to be heavier than fence wire normally carries. Conventional galvanised chain link as commonly sold carries 40 to 60 GSM of zinc: it costs less upfront, and in C3 that coating lasts a few years at the worst end of the category.
Near the sea or chemicals: add a polymer coating
From C4 up, salt and chemicals use up zinc too fast for a metallic coating alone to be practical. The answer is a polymer coating over the metal: a UV-protected PVC or similar coating keeps salt and chemicals off the zinc or Zn-Al, and the metal underneath protects any cut or scratch. In India’s sun, the polymer must be UV-protected, or it becomes brittle and cracks.
- What SIMO Securon offers: SIMO Securon does not make PVC-coated knotted fence. Our engineers advise on the right material and source it, and for large requirements SIMO can make a UV-protected knotted fence.
- At C5 and CX (within about a kilometre of the sea, or inside a chemical plant), have the site surveyed before choosing: our engineers check the salt and chemicals that reach the fence.
- Inside chemical and process plants, ISO 9223 does not apply: the calculator assumes at least C5 and asks for a site review.
SIMO Securon grades by coating
The calculator recommends the lightest SIMO Securon grade that meets your need, and says when the next grade up gives more margin. SIMO Securon Pi carries Zinc, 80 to 100 GSM, with topcoat, Zeta Nova Zn-Al 90/10, 120 GSM and Alpha Zn-Al 90/10, 240 GSM minimum. Pi is recommended only where its zinc alone meets the minimum, so mostly on dry, clean sites; its rated life also counts its topcoat.
| Specification | Pi | Zeta Nova | Alpha |
|---|---|---|---|
| Coating | Zinc, 80 to 100 GSM, with topcoat | Zn-Al 90/10, 120 GSM | Zn-Al 90/10, 240 GSM minimum |
| Salt spray | About 200 hours to red rust (estimated from the coating specification) | 1,200 hours without red rust (tested) | 2,000 hours without red rust (tested) |
| Rated life | 10 years | 20 years | 35+ years |
How the rated lives are worked out is on quality and testing; more on zinc-aluminium coatings in Zn-Al coatings explained. Once you know the grade, the fencing cost calculator works out the posts, rolls and toppings.
More about the fence coating calculator
Why design to the worst end of the category?
Each ISO 9223 category spans a range: in C3, 5 to 15 g/m² of zinc a year, a factor of three. Without measuring your site you cannot know where in that range it falls, so the calculator assumes the worst end. A site at the mild end will see its coating last longer; it will not see it fail sooner.
What the calculator does not cover
Coating life also depends on things no table can see: wire cut or welded on site, which exposes bare steel; fertiliser or manure heaped against the fence; posts that rust and stain the wire; and damage from machines or animals. Correct installation keeps these away. The calculator uses first-year corrosion rates, which ISO 14713-1 also uses to estimate coating life; corrosion often slows after the first years, which adds margin.
Where the figures come from
The categories and zinc loss rates are from ISO 9223:2012; the method, coating mass divided by the rate, is the one ISO 14713-1 uses for zinc coatings. The heaviest zinc coating for fence wire, 290 GSM, is from IS 4826. Zn-Al 95/5 is counted at twice zinc from GalvInfo’s published field studies and EN 10223-6; Zn-Al 90/10 at 2.5 times is SIMO Securon’s own design basis. The calculator estimates; an engineer confirms the category for your site from its PIN code.
FAQ
Fence coating calculator questions
How much zinc coating does a fence need?
It depends on the site and how long the fence must last: multiply the years by the zinc your site's ISO 9223 category uses up each year. Most of inland India is C3, at 5 to 15 g/m² of zinc a year. Designing to the worst end, a 20-year fence needs 300 GSM of zinc, 150 GSM of Zn-Al 95/5 or 120 GSM of Zn-Al 90/10.
What is a corrosivity category?
ISO 9223 sorts outdoor air into six corrosivity categories, from C1 (very low) to CX (extreme), by how fast standard metal samples corrode in their first year. Salt from the sea, sulphur from industry and how long the metal stays wet decide it. The calculator estimates your category from those three, as the standard allows.
Is Zn-Al better than galvanised wire?
For the same coating mass, yes. The calculator counts Zn-Al 95/5 as lasting twice as long as zinc, from published field studies and EN 10223-6. For Zn-Al 90/10 it uses 2.5 times: SIMO Securon's design basis for its own coating, because no standard gives a figure for 90/10.
Why does a site near the sea need a polymer coating?
From C4 up, salt and chemicals use up zinc so fast that the metal alone would have to be heavier than fence wire normally carries, which is 290 GSM under IS 4826. A UV-protected polymer coating, such as PVC, keeps them off the metal. SIMO Securon's engineers advise on the material and source it; for large requirements, SIMO can make a UV-protected knotted fence.
Does the calculator give a price?
No. It gives the coating your site needs and the grade SIMO Securon recommends. Send the form under the result: an engineer checks your site from its PIN code, recommends the fence and sends the price.
Sources
- ISO 9223:2012: Corrosion of metals and alloys. Corrosivity of atmospheres. Classification, determination and estimation (opens in a new tab), ISO
- ISO 14713-1:2017: Zinc coatings. Guidelines and recommendations for the protection against corrosion of iron and steel in structures. Part 1: General principles of design and corrosion resistance (opens in a new tab), ISO
- GalvInfoNote 1.9: Zinc-5% Aluminum Alloy-Coated Steel Sheet (Rev 1.2, December 2017) (opens in a new tab), GalvInfo Center, International Zinc Association
Rather talk it through?
Send your site's PIN code on WhatsApp, or call us. Our engineers check how far it is from the sea and from industry, and recommend the fence and its coating.