GP (galvanised plain) sheets are steel sheets coated with zinc to stop rust. The most important number on a GP order is the coating mass, written as Z followed by a number.
What the number means
The number is the total weight of zinc in grams per square metre, counted on both sides together. So Z275 means about 275 g of zinc per m² of sheet, roughly 137 g on each side. In India, galvanised sheets and coils are covered by IS 277.
| Coating | Zinc (g/m², both sides) | Typical use |
|---|---|---|
| Z90 to Z120 | 90 to 120 | Indoor parts, panels, ducting in dry areas, items that will be painted |
| Z180 | 180 | General purpose, light outdoor exposure |
| Z275 | 275 | Outdoor use, roofing, structures, humid and coastal areas |
More zinc, longer life
Zinc protects steel by corroding first. Roughly speaking, doubling the coating mass doubles the time before the base steel starts to rust in the same environment. Coastal air, industrial fumes and standing water use up zinc faster, so choose a heavier coating there.
Spangle
- Regular spangle shows the familiar flower-like crystal pattern. It is common for general use.
- Zero (minimised) spangle has a smooth, even surface that paints and powder coats better. It is preferred for appliances, panels and furniture.
GP, GI and Galvalume
In the Indian market, GP usually means flat galvanised sheet or coil, and GI often refers to corrugated galvanised roofing sheet. Galvalume (aluminium-zinc coated, with designations such as AZ150) gives longer life outdoors and is popular for roofing and cladding.
How to order
Give us the thickness, width, coating (for example Z120 or Z275), spangle type and quantity. If the sheet will be painted, mention it so we can suggest a zero spangle option.