Overseas buyers routinely receive quotes that mix PPGI and PPGL under the generic label "colour-coated steel." The two products share the same paint chemistries but sit on different metallic substrates, and that difference drives service life, weldability, and price. This guide gives you the procurement decision, not a metallurgy lecture.
What It Is
PPGI (Pre-Painted Galvanized Iron) is cold-rolled steel coil hot-dip coated with zinc (GI substrate), then coil-coated with a primer, top coat, and back coat.
PPGL (Pre-Painted Galvalume / Aluzinc) uses the same coil-coating paint system on a hot-dip aluminium-zinc alloy substrate (commonly around 55% Al / 43.4% Zn / 1.6% Si by mass, referenced under standards such as ASTM A792 or EN 10346 AZ designations — verify against the current issue of the applicable standard).
Both are supplied as coils, sheets, or slit strip. To compare offers fairly, separate three layers of performance:
- Metallic coating (Zn vs Al-Zn, coating weight in g/m²).
- Paint system (primer + top coat + back coat chemistry and thickness).
- Finished-product / design factors (panel geometry, drainage, cut-edge and fastener detailing, joining method).
Each layer contributes independently — a "better substrate" cannot compensate for an inadequate paint spec or a poor panel design.
Standards Notice
Designations across ASTM (A653 / A792), EN 10346, JIS (G3312 / G3321), and GB/T (12754 / 12755) are not automatically interchangeable. Grade names, coating designations, minimum coating weights, and acceptance criteria differ between systems, and each standard is updated periodically.
Before ordering, confirm with the mill or supplier that the specific grade, coating weight, and acceptance test they quote correspond to the standard cited in your project specification. Do not rely on a nominal cross-reference table alone.
When Each One Typically Fits
These are default starting points, not absolute rules. Always confirm against the project specification, applicable standard, and service environment.
PPGL is often a reasonable starting point when: - The panel is installed on a roof or facade with limited cut-edge exposure and adequate drainage. - Long atmospheric service life on flat surfaces is a priority and the environment is dry to moderately humid. - Higher solar reflectivity of the Al-Zn substrate is desirable.
PPGI is often a reasonable starting point when: - The end use is interior (partitions, ceiling, appliance skins) or decorative. - The assembly involves welding, heavy forming, on-site cutting, or field repainting. - The applicable national standard, code, or tender document explicitly requires a galvanized substrate. - Cut edges, perforations, and fastener penetrations are frequent and cathodic protection is preferred.
In every case, the paint system (PE / HDP / SMP / PVDF) and the finished-panel design (profile, laps, fasteners, edge trim, drainage) should be specified alongside the substrate — not after it.
What to Compare
When evaluating offers, place them side-by-side on these dimensions before comparing price. Separate metallic-coating, paint-system, and finished-product factors so you can see where each supplier is actually differentiating.
Metallic coating - Substrate type: GI (Zn) vs GL / AZ (Al-Zn). - Coating weight in g/m² total both sides (e.g. Z100, Z275, AZ70, AZ150) — a higher number means more metal per m². - Base steel grade and applicable standard (e.g. EN 10346 DX51D, JIS G3312 CGCC / G3321 CGLCC, ASTM A653 / A792, GB/T 12754 / 12755). Confirm the standard issue year.
Paint system - Chemistry: polyester (PE), HDP, SMP, PVDF. - Top coat, primer, and back coat thickness in microns (published PE and PVDF ranges vary by supplier — request the specific spec). - Gloss level, colour reference (RAL / NCS / supplier chart), and colour tolerance. - Test data referenced against the offered spec: salt spray hours (e.g. ASTM B117), T-bend, impact, adhesion, QUV.
Finished-product / commercial - Base thickness, width, length, and tolerances. - Coil ID / OD, coil weight, packaging, and marking. - MOQ, Incoterms, port of loading, lead time, payment terms. - Paint-film warranty statement: covered failure modes, exclusions, and required maintenance — read it in full before accepting.
Do not accept generic phrases like "anti-corrosion coating" without the substrate designation, coating weight, and paint spec.
What to Request from Suppliers
Ask every shortlisted supplier for the same evidence, referenced to the exact spec you intend to order — not a generic company brochure:
- Technical datasheet for the specific substrate + paint system offered.
- Mill Test Certificate (MTC) citing the applicable standard and issue year.
- Written paint-film warranty with defined failure modes, exclusions, and any environment or maintenance conditions.
- Salt-spray, T-bend, impact, and adhesion test results on the offered spec.
- Physical colour swatch matching the specified RAL / NCS reference.
- Packing photos from a recent comparable shipment.
- Loading port, typical vessel schedule, and available Incoterms options.
Send the same substrate, coating weight, paint system, colour, and quantity to every supplier — otherwise you are comparing different products.
What to Do Next
Fix the metallic-coating spec, paint system, colour, and finished-panel requirements in writing. Then send the RFQ template below to at least three verified MercatusX suppliers, compare on total landed cost and documented performance evidence — not $/ton alone — and confirm the offered grade against your project standard before placing the order.
PPGI vs PPGL — factors to compare (not a verdict)
| Factor | PPGI (Pre-Painted GI) | PPGL (Pre-Painted Galvalume / AZ) |
|---|---|---|
| Metallic coating | Pure zinc (Zn) | Aluminium-zinc alloy (~55% Al / ~43.4% Zn / ~1.6% Si) |
| Common coating designations | Z100, Z180, Z275 (g/m², total both sides) | AZ50, AZ70, AZ100, AZ150 (g/m², total both sides) |
| Reference standards (verify issue year) | EN 10346, ASTM A653, JIS G3312, GB/T 12754 | EN 10346 (AZ), ASTM A792, JIS G3321, GB/T 12755 |
| Cut-edge / scratch protection | Sacrificial (cathodic) protection from zinc | Primarily barrier protection; cathodic contribution generally lower |
| Flat-surface atmospheric behaviour | Well established in a wide range of environments | Often specified where flat-surface longevity in dry/moderate climates is a priority — validate against supplier test data for your environment |
| Heat reflectivity of substrate | Lower | Higher (lighter Al-Zn surface) |
| Weldability / heavy forming | More tolerant | Less tolerant; consult supplier guidelines |
| On-site repainting | Generally easier | Requires a primer suitable for Al-Zn substrates |
| Typical starting-point uses (verify per project) | Appliances, interior panels, decorative sheet, some roofing applications | Roofing, facades, long-span panels where cut-edge exposure is limited |
| Relative unit price | Often lower at equivalent paint spec | Often at a premium at equivalent paint spec |
Typical spec ranges seen in export offers (verify per order)
| Attribute | Typical range |
|---|---|
| Base thickness | 0.18 – 1.20 mm |
| Width | 600 – 1250 mm |
| Zinc coating (PPGI) | Z40 – Z275 g/m² total both sides |
| Al-Zn coating (PPGL) | AZ30 – AZ150 g/m² total both sides |
| Primer thickness | 5 – 7 μm |
| Top coat thickness | 15 – 25 μm (PE), 25 – 35 μm (PVDF) |
| Back coat thickness | 5 – 10 μm |
| Paint systems | Polyester (PE), HDP, SMP, PVDF |
| Coil ID | 508 mm or 610 mm |
| Coil weight | 3 – 8 t (project dependent) |
Buyer checklist
- State the substrate explicitly: PPGI (Zxxx) or PPGL (AZxx) — never accept 'colour-coated steel' alone.
- Fix the metallic coating weight in g/m² total both sides (e.g. Z100, AZ70) and require it on the MTC.
- Specify the paint system, top coat and back coat thickness, and gloss level separately from the substrate.
- Cite the applicable base steel grade and standard including issue year (e.g. EN 10346:latest DX51D+AZ, ASTM A792 CS Type B).
- Confirm with the supplier that quoted designations map correctly to the standard in your project specification — do not assume cross-standard equivalence.
- Provide RAL / NCS colour reference and require a physical sample approved in writing before mass production.
- Require a written paint-film warranty naming covered failure modes, exclusions, and any maintenance / environment conditions.
- Require test evidence (salt spray, T-bend, impact, adhesion) on the offered spec — not brochure figures.
- Confirm thickness, width, and length tolerances in writing.
- Confirm coil ID, packaging (VCI paper, wooden pallet, sea-worthy packing), and marking.
- State intended application, forming/joining process, and service environment in the RFQ so the supplier can flag unsuitable specs.
- Confirm Incoterms, port of loading, lead time, and payment terms before comparing $/ton.
Common buyer mistakes
- Comparing PPGI and PPGL prices without matching coating weight and paint thickness.
- Treating 'Galvalume' and 'galvanized' as interchangeable — they behave differently at cut edges.
- Trusting a generic brochure salt-spray number instead of test data on the offered spec.
- Choosing PPGL for heavily perforated or welded assemblies where cathodic protection matters.
- Skipping the physical colour sample and relying only on a RAL code across different paint systems.
- Ignoring back-coat thickness and packaging spec, then losing coils to transit damage.
Frequently asked questions
Is PPGL always better than PPGI for roofing?
Not always. For flat, well-drained roofs with limited cut-edge exposure, PPGL at an appropriate AZ coating weight typically offers longer atmospheric life. For panels with many cut edges, perforations, or welded joints, PPGI's stronger cathodic protection at damage sites can outperform PPGL. The environment and detailing matter more than the substrate name.
What coating weight should I specify?
There is no single answer — it depends on climate, warranty target, and cost tolerance. Ask each supplier to recommend a coating weight for your climate and warranty, and require them to justify it against their own test data and warranty terms.
Can I paint PPGL and PPGI with the same top coat?
The same paint chemistries (PE, HDP, SMP, PVDF) are used on both substrates, but the primer chemistry differs. Always confirm the exact paint system on the datasheet — do not assume 'PVDF is PVDF' across suppliers.
Which is easier to fabricate on site?
PPGI is generally more forgiving to bend, weld, and repaint. PPGL is more sensitive to heavy forming and requires an Al-Zn compatible primer for on-site touch-up.
How do I compare offers fairly?
Fix the substrate, coating weight, base grade, paint system, top/back coat thickness, colour, and tolerance in writing. Send the same spec to every supplier. Only then compare price, lead time, and payment terms.
What standards should the MTC reference?
Common export references are EN 10346, ASTM A653 (GI), ASTM A792 (GL/AZ), JIS G3312 (CGCC), JIS G3321 (CGLCC), and GB/T 12754/12755. The MTC should quote the standard the offer is priced against.
Does PPGL cost more than PPGI?
Usually yes at equivalent paint spec, but the premium varies with aluminium and zinc prices. Always ask both PPGI and PPGL suppliers to quote the same paint spec so the substrate premium is visible in the numbers.
Ready-to-use RFQ template
Copy this template into an email to a supplier, or send it directly through MercatusX.
**RFQ — Pre-Painted Steel Coil (PPGI / PPGL)** *Substrate and metallic coating* - Product: [PPGI or PPGL] - Base standard, grade, and issue year: [e.g. EN 10346:latest DX51D+Z, or ASTM A792 CS Type B AZ] - Metallic coating weight: [e.g. Z100 or AZ70, g/m² total both sides] *Paint system* - Paint chemistry: [PE / HDP / SMP / PVDF] - Top coat thickness: [μm] - Back coat thickness: [μm] - Colour reference: [RAL / NCS / supplier chart + gloss level] *Geometry and tolerances* - Base thickness × width × length / coil: [e.g. 0.45 mm × 1000 mm × coil] - Thickness tolerance: [e.g. ± 0.02 mm] - Coil ID / coil weight: [e.g. 508 mm ID / 5 t max] *Intended use and environment* (so the supplier can flag unsuitable specs) - Application: [e.g. metal roofing, wall cladding, sandwich panel skin, appliance body, ceiling panel] - Forming / joining process: [e.g. roll-forming, stamping, bending, welding, rivet / self-drilling screw] - Service environment: [e.g. inland industrial, coastal (distance to sea), tropical high-humidity, cold-dry, high-UV — describe realistically] - Design service life expected by client: [years, informational only — no supplier warranty implied] *Inspection and acceptance criteria* - MTC required, citing the standard and issue year quoted above - Test evidence on the offered spec: salt spray (e.g. ASTM B117, hours as offered), T-bend, impact, adhesion, gloss retention — no brochure substitutes - Physical colour swatch approved in writing prior to mass production - Visual acceptance criteria: coating uniformity, edge quality, no cracks / peeling / colour deviation beyond agreed tolerance - Dimensional acceptance: thickness, width, length, camber, waviness within agreed tolerances - Pre-shipment inspection: [self / third-party, e.g. SGS, BV, TÜV] — specify scope - Written paint-film warranty letter: covered failure modes, exclusions, environmental / maintenance conditions *Commercial* - Quantity / MOQ: [e.g. 100 t] - Packaging: [sea-worthy, VCI paper, wooden pallet, eye-to-sky / eye-to-wall] - Destination port: [e.g. Jeddah, KSA] - Incoterms: [e.g. CIF Jeddah] - Payment terms: [e.g. 30% TT advance, 70% against copy of B/L] - Required documents: [MTC, packing list, CO, paint-film warranty letter] - Required delivery: [target ETD / ETA]
Related market intelligence
Check the latest Chinese export prices, supply movements and demand signals before you request a quotation.
Verified suppliers
Every RFQ submitted through MercatusX is matched to verified Chinese mills and trading partners. You receive comparable, procurement-ready quotations — not cold sales pitches.
There is no universally better option between PPGI and PPGL — the right choice depends on the applicable standard, service environment, forming and joining process, and paint-system requirements. Fix the substrate, coating weight, paint system, colour, and finished-panel requirements in writing, then send the RFQ template to at least three verified MercatusX suppliers and compare on documented performance and total landed cost.