Guide
Hot-Dip Galvanized Steel Grating Explained
By DONGFU GRATING Engineering Team · Published 2026-06-24 · Updated 2026-07-17
Hot-dip galvanized steel grating is carbon steel grating that is fully fabricated — welded, cut, banded and drilled — and then immersed in molten zinc at about 450 °C. Fabricating first is essential: the zinc seals every weld point, cut edge and hole in one continuous coating, which pre-galvanized or electro-galvanized alternatives cannot match. Coating quality is governed by the agreed standard, typically ASTM A123 or ISO 1461, which set minimum coating thicknesses by steel section thickness rather than one fixed micron figure. Responsible suppliers verify actual thickness with calibrated magnetic gauges and report results per batch in inspection documentation. Buyers should state the governing standard, ask how thickness is measured and reported, and store panels dry and ventilated to limit wet-storage staining. Very tall, thin bearing bars carry distortion risk in the zinc bath and are reviewed before production. Properly specified and verified, hot-dip galvanizing is the default corrosion protection for outdoor steel grating.
Why grating is galvanized after fabrication
Welding after galvanizing burns the zinc off at every weld, and cut edges expose bare steel. Fabricating the complete panel first — welding, cutting, banding, drilling — and then dipping it coats welds, edges and holes in one continuous layer. This is why "hot-dip galvanized after fabrication" is the standard phrasing on export grating specifications.
At about 450 °C the zinc metallurgically bonds to the steel, forming zinc-iron alloy layers topped by pure zinc. The coating protects as a barrier and also acts sacrificially at small scratches, which is what makes it the default finish for outdoor carbon steel grating.
HDG compared with other finishes
| Finish | Process | Corrosion protection | Typical use |
|---|---|---|---|
| Hot-dip galvanized | Fabricated panel dipped in molten zinc at ≈ 450 °C | High — the default for outdoor grating | Outdoor platforms, walkways, trench covers, coastal sites |
| Electro-galvanized (zinc plated) | Thin zinc layer applied electrolytically | Low — indoor or temporary duty only | Indoor, low-corrosion or short-term projects |
| Painted / powder coated | Primer and topcoat over prepared steel | Depends on coating system and environment | Color coding, safety yellow edges, architectural use |
| Mill finish (untreated) | No coating after fabrication | None — bare carbon steel rusts outdoors | Dry indoor areas, or customer post-processing |
Standards and how thickness is verified
- Grating can be galvanized and tested per ASTM A123 or ISO 1461, or a customer-specified standard — confirmed at order stage
- These standards set minimum coating thickness by steel section thickness, not one fixed micron number
- Actual coating thickness is measured with calibrated magnetic gauges, batch by batch
- Inspection reports with measured values are provided with the order — request them at inquiry stage
Common HDG issues and how they are managed
- Wet-storage staining (white rust): a cosmetic film that forms when fresh zinc stays damp in transit or storage. Prevent it with ventilated bundling and dry, ventilated site storage; it weathers away and does not significantly reduce protection.
- Distortion: very tall, thin bearing bars — for example 3 mm thick at 50 mm depth or more — can warp in the hot zinc bath. Such high-thin designs are reviewed before production; added thickness or press-locked construction may be advised.
- Small blind openings under about 50 mm can bridge with zinc. Flag them on drawings so our technicians can review venting and drainage.
What to include in your galvanizing specification
- The governing standard — ASTM A123 / ISO 1461, a project standard, or "advise me"
- Panel designs flagged for distortion review where bearing bars are tall and thin
- Drainage and venting details for hollow sections or small openings
- Storage and site handling expectations for long sea freight
- Inspection documentation required with shipment
Common Mistakes to Avoid
- Specifying one fixed micron figure instead of a standard — thickness requirements vary by steel section, so standards like ASTM A123 define the minimums
- Expecting electro-galvanized grating to perform outdoors like HDG — it is an indoor-duty coating
- Designing 3 mm thick bars at 50 mm depth or more for HDG without a distortion review
- Storing freshly galvanized panels flat-stacked and wrapped airtight in humid conditions, then finding white rust at site
- Welding or cutting galvanized panels on site without touching up the coating