GI (galvanized, pure zinc) is the economy workhorse: easiest to weld and bend, lowest cost. GL/Aluzinc (55% aluminium-zinc) lasts 2–4× longer bare, ideal for unpainted roofing. PPGI is GI or GL pre-painted — choose it when appearance matters and you want the factory paint warranty. Coating weight is the lifespan dial: Z275 GI in a rural environment runs 20+ years to red rust. Nikasteel supplies Z60–Z350 GI, AZ150 GL and PPGI in 0.13–3.0 mm, MOQ 25 tons.
Every coated coil quote starts with three letters and a number: GI Z275, GL AZ150, PPGI 0.5×1000 RAL 9016. Buyers who understand what those codes mean get accurate lifespans, avoid paying for coating they don't need, and never argue with a contractor about warranty. Here is the practical guide.
The Four Coated Products
| Product | Coating | Substrate | Look | Common use |
|---|---|---|---|---|
| GI | Pure zinc, hot-dip | HR or CR strip | Spangled or minimised-spangle grey | Roofing, ducting, panels, tubes, purlins |
| GL / Aluzinc | 55% Al–43.4% Zn–1.6% Si | CR strip | Fine spangle, bright silver | Bare roofing, solar mounting, cladding |
| PPGI | GI or GL + paint (PE/HDP/PVDF) | CR strip | Any RAL colour, matte or gloss | Visible roofing, appliances, facades |
| Galvalume® | Brand name of GL (BIEC) | CR strip | As GL | As GL — licensed mills only |
Coating Weight = Lifespan Dial
| Class | GI (g/m² both sides) | GL (g/m²) | Typical first-maintenance, rural |
|---|---|---|---|
| Light | Z60–Z120 | AZ70–AZ100 | 5–10 years (interior/short-term) |
| Standard | Z180–Z275 | AZ150 | 15–25 years |
| Heavy | Z350–Z450 | AZ185–AZ255 | 30+ years / coastal-industrial |
Rules of thumb: coastal air cuts GI life roughly in half; industrial pollution similarly. GL tolerates bare exposure better than GI — its aluminium-rich phase forms a stable oxide that self-passes.
Formability and Welding
- GI welds and bends most easily; zinc burns off at the weld, so ventilate. Bending after coating cracks zinc at tight radii — order bending-quality (BQ) or post-galvanize the bend.
- GL is harder on tooling at deep draws; use bending-quality grades and lubricate. Roofing profiles roll beautifully.
- PPGI must be formed before it ships: the paint line is the last step. Specify T-bend rating (e.g. 2T–3T for PE, up to 6T for flexible systems) and pencil hardness when ordering.
Specifying PPGI Correctly
- Paint system: PE (polyester, 15–20 µm) for standard; HDP (35 µm) for coastal; PVDF (25 µm) for premium architecture; SMP for mid-life industrial.
- Coating class of substrate: PPGI on Z150 vs Z275 changes the cut-edge life even where paint covers faces.
- Reverse side: 5–7 µm backing coat standard; specify colour if visible.
- Gloss and colour: RAL or custom; gloss 20–80 GU. Confirm the colour stays within the mill's batch tolerance run.
Five Buying Rules
- Match coating to environment — see the lifespan table; do not buy Z120 for coastal roofing to save US$8/ton.
- Ask for passivation (CR3+ or chromium-free) and oiling on GI/GL to prevent white rust in transit — especially for sea freight to humid markets.
- Confirm spangle type if visible: regular, minimised or zero-spangle changes appearance under paint.
- Check coil IDs match MTCs — heat number, gauge, coating weight, and tensile data per EN 10204.
- For PPGI, ask for a painted sample panel from the actual production batch — not a colour card — before the balance ships.
See our GI coil and PPGI coil pages for live gauges and coating classes, or the HR vs CR guide for the substrate story.
Coated Coils, Quoted in 24 Hours
GI Z60–Z350, GL AZ150, PPGI PE/HDP/PVDF — 0.13–3.0 mm × 600–1500 mm, MOQ 25 tons, MTC EN 10204 3.1 with every shipment.
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