Galvanised steel is sold by its zinc coating, written as Z120, Z180, Z275 and so on. The number is the zinc in grams per square metre, counting both faces of the sheet. More zinc means longer protection — but it also costs more, so it pays to match it to where you live.
What the numbers mean
- Z120 — 120 g/m² in total, about 60 g on each face: roughly 8–9 microns of zinc per side.
- Z275 — 275 g/m² in total, about 137 g on each face: roughly 19 microns per side — more than twice the zinc.
Zinc protects steel by corroding slowly in its place, so the protection lasts roughly in proportion to the amount of zinc. Twice the zinc gives roughly twice the life in the same conditions.
Which one for your house?
- Inland Kerala (most of Palakkad, inland Malappuram and Thrissur): Z120 with an epoxy primer and a good top coat is a sound, economical choice.
- Within a few kilometres of the sea: salt in the air attacks zinc much faster — choose Z275 and a marine-grade paint system.
- Bathrooms and kitchens: the paint matters more than the zinc grade — keep it intact.
What zinc does not do
No galvanised window is rust-proof forever. Welds burn the zinc away and cut edges are bare, which is why every LINEA weld gets zinc-rich repair and the whole window is epoxy-primed. Keep the paint unbroken and the zinc does the rest.
LINEA's standard is TATA Galvano Z120; Z275 is available for coastal sites — ask for both prices on the same quotation.