Hot-dip galvanising coats steel with zinc by dipping the cleaned part in molten zinc at about 450 °C. The zinc bonds with the steel in layers and protects it for many years outdoors, even where it is scratched. It is used on structures, towers, fencing, fasteners and fabricated frames.
Quick facts
- Process temperature
- About 445–460 °C molten zinc
- Coating thickness
- About 45–100 µm, more on thick steel
- Life outdoors
- Often 20 years or more, depending on the environment
- Coverage
- Inside and outside, including corners and hollow parts with vent holes
- Common standard
- IS 4759 / ISO 1461
- Usually priced
- Per kg of steel galvanised
How it is done
- Degreasing to remove oil and paint marks
- Pickling in acid to remove rust and mill scale
- Fluxing so the zinc wets the steel
- Dipping in molten zinc for a few minutes
- Cooling in air or water, then inspection of coating thickness
Galvanising or zinc plating?
| Hot-dip galvanising | Zinc electroplating | |
|---|---|---|
| Thickness | About 45–100 µm | About 5–25 µm |
| Outdoor life | Decades | Months to a few years |
| Finish | Grey, rougher, spangle possible | Bright, smooth, passivated colours |
| Suits | Structures, fabrication, outdoor parts | Small precise parts, fasteners, brackets |
What to tell the galvaniser
- Steel grade (silicon and phosphorus content change the coating)
- Weight and largest size of the parts
- Required coating thickness or standard
- Vent and drain holes in hollow sections (the galvaniser can advise)
- Threads or holes that must be cleaned or masked
- Whether parts will be painted afterwards (duplex system)
Need hot-dip galvanising done?
Post your requirement free. Workshops that take your kind of work see it and get in touch. You only talk to the ones that fit.
Get startedRelated
Materials
Questions
- How thick is hot-dip galvanising?
- Typically about 45–100 µm. Thicker steel sections pick up more zinc; ISO 1461 and IS 4759 set minimum average thickness by steel thickness.
- Can galvanised steel be painted or powder coated?
- Yes, after proper surface preparation (sweep blasting or a suitable primer). Galvanising plus paint is called a duplex system and lasts longer than either alone.
- Why do hollow parts need holes before galvanising?
- Air and moisture trapped inside expand violently in molten zinc, and zinc must flow in and out. Vent and drain holes make galvanising safe and the coating complete.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 16 October 2026.