The standard behind the 610 g/m² line in almost every state utility purchase specification. Here is the table, the conversion into microns, and what we certify against it.
IS 4759 specifies the minimum mass of zinc that must remain on hot-dip galvanized structural steel, expressed in grams per square metre of surface. It is the requirement clause — IS 2629 governs how the coating is applied, IS 4759 governs how much of it there has to be.
The figure most buyers quote is 610 g/m², which applies to sections over 5 mm thick. Because it is written as a mass and inspected as a thickness, the conversion matters: at a zinc density of 7.14 g/m² per micron, 610 g/m² is approximately 85 microns.
Minimum mass of zinc coating by article thickness.
| Steel thickness | Minimum coating mass | Approx. equivalent thickness |
|---|---|---|
| Over 5 mm | 610 g/m² | ≈ 85 microns |
| 3 mm to 5 mm | 460 g/m² | ≈ 64 microns |
| 1.5 mm to 3 mm | 395 g/m² | ≈ 55 microns |
Conversion uses 7.14 g/m² of zinc per micron of coating — divide the mass by 7.14 to get the thickness. The standard states the requirement as mass; a DFT gauge reads thickness, which is why the two numbers appear side by side on our inspection reports.
Read this before writing 610 g/m² into an order.
A mass average can pass while a corner fails. That is what the dip test is for.
Answered from our own line, not from the standard's cover page.
Approximately 85 microns. Zinc runs about 7.14 g/m² per micron of coating, so 610 divided by 7.14 gives roughly 85. A DFT gauge reads thickness while the standard states mass, so both numbers belong on the inspection report.
It is set by the steel thickness, not by the product: over 5 mm calls for 610 g/m², 3 to 5 mm for 460 g/m², and 1.5 to 3 mm for 395 g/m². Send the drawing and we will confirm the grade against each section in it.
Yes, and we confirm it in writing at quotation against your section thicknesses. Our published standard range is 75–85 microns; a 610 g/m² requirement is met at the top of that range or above, and we certify the mass rather than only the gauge reading.
By the stripping method in IS 6745 — the specimen is weighed, the zinc dissolved in inhibited acid, and the specimen reweighed, giving mass per unit area directly. Thickness by DFT gauge is the faster production check; stripping is the referee method.
They serve the same purpose but express it differently. IS 4759 states a coating mass in g/m²; ASTM A123 states coating grades in microns by material category and steel thickness. We treat them as equivalent practice and quote against whichever the buyer specifies — we do not claim to hold either as a certification.
Yes. Mill test certificates for the steel and a galvanizing inspection report for the coating travel with the consignment, along with the packing list and, for export, the certificate of origin.
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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