Three specifications, three sets of units, one question: how much zinc is actually on the steel? The comparison an engineer needs and almost nobody has written.
The short answer: two of the three agree and one does not. IS 4759 and EN ISO 1461 both arrive at 610 g/m², about 85 microns, for heavy structural sections — by completely different routes, one stating a mass and the other a thickness. ASTM A123 asks for 100 microns on structural shapes over a quarter inch.
That 15-micron difference is roughly 18% more zinc. On a large tonnage it is real money, and it is the single most common reason an American specification and a European one cannot be quoted at the same rate. If a buyer says “galvanized to international standard” without naming one, that question is still open.
The case that covers most tower, gantry and fabrication work.
| IS 4759 | EN ISO 1461 | ASTM A123 | |
|---|---|---|---|
| Requirement | 610 g/m² | 85 µm mean, 70 µm local | 100 µm (Grade 100) |
| In the other unit | ≈ 85 µm | ≈ 610 / 505 g/m² | ≈ 714 g/m² |
| Stated as | Coating mass | Thickness — two figures | Thickness — one figure |
| Varies by | Steel thickness | Article thickness | Material category and thickness |
| Is there a local minimum? | Uniformity by dip test | Yes — 70 µm | Minimum average only |
| Uniformity method | IS 2633 copper sulphate dip | Local thickness on reference areas | Visual finish and adherence |
| Referee method | IS 6745 stripping | Weighing / magnetic | Weighing / magnetic |
The EN ISO 1461 local figure is the one that catches suppliers out. A coating can meet the 85 µm mean and still fail on a corner at 65 µm. IS 4759 goes after the same problem with a dip test rather than a second number; ASTM A123 is the most forgiving of the three on this specific point, because it states a minimum average and no local floor.
| Steel thickness | IS 4759 | EN ISO 1461 (local / mean) | ASTM A123 structural shapes |
|---|---|---|---|
| Over 6 mm | 610 g/m² (≈ 85 µm) | 70 / 85 µm | 100 µm over ¼ in |
| 3 to 6 mm | 460 g/m² (≈ 64 µm) | 55 / 70 µm | 75 µm, 1/8 to ¼ in |
| 1.5 to 3 mm | 395 g/m² (≈ 55 µm) | 45 / 55 µm | 65 µm, 1/16 to 1/8 in |
| Under 1.5 mm | — | 35 / 45 µm | 45 µm under 1/16 in |
The thickness bands do not line up exactly — the Indian standard splits at 5 mm and 3 mm, the European at 6 mm and 3 mm, and the American in fractions of an inch. On material near a boundary, check which band your section actually falls in under the standard being quoted.
We galvanize to the figure you name and issue the coating readings per batch, open to third-party inspection by SGS, Bureau Veritas, TÜV, DNV or Intertek at your cost. Our published standard range is 75–85 microns; a 610 g/m² or 85 µm mean requirement is met at or above the top of that range and certified, confirmed in writing at quotation against the section thicknesses in your drawing. A 100 µm ASTM A123 Grade 100 requirement is a heavier coating and is quoted as such rather than absorbed silently.
We do not hold any of these three as a certification, and neither does any other galvanizer. They are specifications a coating is supplied against.
Answered from our own line, not from the standard's cover page.
On heavy structural shapes, yes. A123 asks for a 100 micron minimum average where IS 4759's 610 g/m² works out at about 85 microns — roughly 18% more zinc. On uniformity the picture reverses: EN ISO 1461 sets a local minimum and IS 4759 requires a dip test, while A123 states only a minimum average.
For heavy sections they land on the same number: EN ISO 1461 requires an 85 micron mean above 6 mm, and IS 4759's 610 g/m² above 5 mm converts to about 85 microns. The difference is that EN ISO 1461 also sets a 70 micron local minimum that no single reference area may fall below.
The lowest coating thickness permitted on any single reference area of the article, as distinct from the average across it. It exists so that a thin corner cannot be hidden by a generous average, and it is what makes an EN ISO 1461 inspection more searching than an average-only one.
IS 4759 for Indian supply, EN ISO 1461 for European specifications, ASTM A123 plus ASTM A153 for American ones. Whichever you choose, state the grade or figure and the section thickness — the standard name alone does not specify a coating.
Yes. We galvanize to the figure named and certify the readings. What we will not do is claim to be certified to any of them, because no galvanizing plant is — they are product specifications, not plant certifications.
Tell us the standard, the coating requirement and the component, and we will confirm in writing what we can hold and how we will certify it. Galvanizing is on our own floor, so the answer comes from us and not from a sub-contractor.
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