The Complete Guide to Galvanization
ENSOL Engineering TeamUpdated 2026-02-253 min read
Galvanization protects steel from corrosion with a zinc coating. This guide compares the common coatings (GP, GL, ZAM, HDGI), explains the hot-dip process, and helps match a coating to the environment.
Key takeaways
- Zinc protects steel as a barrier and sacrificially.
- GP is thin (sheltered use); HDGI is thick, edge-to-edge (ground-mount, coastal).
- ZAM self-heals cut edges; GL is a strong aluminium-zinc barrier.
- Coating thickness, verified to IS 4759 / ISO 1461, drives life.
The common coatings
GP (pre-galvanised) is thin with exposed edges; GL (Galvalume) is a ~55% aluminium-zinc barrier; ZAM adds magnesium for self-healing edges; and HDGI (hot-dip) gives the thickest, full-coverage protection.
The hot-dip process
Steel is degreased, pickled and fluxed, then immersed in molten zinc at ~450 °C to form bonded zinc-iron layers. Coating thickness is inspected against IS 4759 / ISO 1461, with NABL-verified checks.
Choosing a coating
Match the coating to the environment's corrosivity: sheltered rooftops can use GP or GL; ground-mount and coastal sites need HDGI or ZAM. Specify and verify coating thickness rather than choosing on price alone.