Most steel windows in Kerala are now made from galvanised (GI) steel rather than plain mild steel (MS). Here is what the difference is, and where it still matters.
MS and GI in one line each
- MS (mild steel) is bare steel. It rusts as soon as the paint is scratched or worn.
- GI (galvanised iron/steel) is the same steel with a zinc coating applied at the steel mill. Zinc corrodes first and protects the steel, even at small scratches.
What "120 GSM" means
The zinc coating is measured in grams per square metre (GSM), counting both faces. Z120 carries 120 g/m²; Z275 carries 275 g/m² and lasts longer in harsh conditions. For most Kerala homes Z120 with a good paint system is sound; for sites within a few kilometres of the sea, choose Z275.
The weak spot: welds and cut edges
Welding burns the zinc off around every joint, and cut edges are bare steel. That is where rust starts on galvanised windows. Each weld should be cleaned and coated with zinc-rich paint, and the whole window primed — LINEA treats every weld and finishes with epoxy primer before dispatch.
Painting and upkeep
Galvanised windows still need paint: an epoxy primer and a good top coat, renewed every few years on the weather side. Keep drainage slots in the sill clear so water does not stand in the frame.
Where MS still makes sense
Thick plates and solid bars — hinge reinforcement plates, some grills — are often mild steel. That is fine when they are fully primed and painted.