What is HDGI? Hot-Dip Galvanised Iron Explained
ENSOL Engineering TeamPublished 2026-02-011 min read
HDGI — hot-dip galvanised iron/steel — is steel that has been dipped in a bath of molten zinc after fabrication, forming a metallurgically bonded zinc-iron coating over every surface, including cut edges, welds and internal faces. It is the most durable of the common coatings ENSOL offers and is preferred for ground-mount and coastal structures.
How hot-dip galvanising works
The fabricated member is cleaned (degreased and acid-pickled), fluxed, then immersed in molten zinc at around 450 °C. Zinc reacts with the steel surface to form a series of zinc-iron alloy layers topped by pure zinc.
Because the part is dipped whole, the coating covers edges, holes and welds that in-line coatings leave exposed.
Why HDGI lasts
The coating protects in two ways: as a barrier, and sacrificially — zinc corrodes in preference to the steel it protects. The thicker the zinc, the longer the life, so HDGI's heavy coating gives the longest maintenance-free service, up to about 25 years depending on the environment.
In humid, industrial or coastal atmospheres this edge-to-edge, high-mass protection is decisive.
Where HDGI is the right choice
ENSOL recommends HDGI for ground-mount solar structures, coastal and high-humidity sites, and any structure where long life with minimal maintenance matters most. For sheltered rooftop work, lighter pre-galvanised sections are often sufficient.