Sep 14, 2026 · 10 min read

PPGL vs PPGI for Roofing and Wall Cladding

For most exterior roofing and wall cladding exposed to rain, humidity, salt or industrial atmosphere, PPGL (prepainted galvalume / zinc-aluminium coated steel) is usually the stronger default choice, because its aluminium-rich metallic coating tends to resist atmospheric corrosion better than a plain zinc coating of similar mass. Choose PPGI (prepainted galvanized steel) when the environment is mild, the cut-edge and forming behaviour of zinc suits your process, or when project specifications, budget or availability point that way. The right answer is never absolute: it depends on substrate, coating mass, paint system, environment, forming method and maintenance. This article gives you a decision matrix, a specification table, an RFQ checklist and the mistakes that most often cause disputes.

What PPGL and PPGI Actually Are

Both products start as cold-rolled steel coil, receive a metallic coating, then receive a paint system (typically primer plus topcoat, sometimes with a back coat). The difference is the metallic coating underneath the paint.

PPGI: prepainted galvanized steel

PPGI uses a zinc coating, normally applied by hot-dip galvanizing. Zinc protects steel in two ways: it acts as a barrier, and it sacrifices itself preferentially at scratches and cut edges (galvanic or cathodic protection). Zinc coating mass is commonly expressed in g/m² (both sides combined) or as a coating class. Refer to PPGI coil for product-level details, and confirm the exact coating designation your contract requires.

PPGL: prepainted galvalume steel

PPGL uses a zinc-aluminium metallic coating, typically around 55% aluminium, 43.4% zinc and 1.6% silicon by weight in the common alloy, although compositions and trade names vary by producer. The aluminium-rich phase gives good resistance to atmospheric corrosion and to high-temperature oxidation, while the zinc fraction still provides some sacrificial protection at damaged areas. See galvalume steel coil for coating and finish options. Because the coating is not pure zinc, cut-edge protection is generally weaker than PPGI at the same coating mass, and this matters for narrow, heavily sheared profiles.

PPGL vs PPGI: The Decision Matrix

Use the table below as a starting point, then confirm every value against your project specification, the applicable standard edition and the supplier’s dated offer. It is general industry guidance, not a substitute for contract-specific requirements.

Decision factor	PPGI (zinc-coated)	PPGL (zinc-aluminium coated)
Typical atmospheric corrosion resistance	Good in mild to moderate environments	Generally better in many atmospheric exposures, especially where aluminium oxide films are stable
Cut-edge / scratch protection	Stronger sacrificial protection from zinc	Weaker sacrificial action; edges and drilled holes need attention
High-temperature exposure	Zinc can be more affected by sustained heat	Often preferred where moderate heat and oxidation resistance matter
Alkaline or acidic contact	Zinc is sensitive to strong acids and alkalis	Also sensitive; neither coating is a chemical barrier on its own
Coastal / salt-laden air	Usable with adequate coating mass and paint system	Commonly specified where salt exposure is significant
Forming and bending	Well established for roll forming	Requires correct paint flexibility and bend radius control
Welding and joining	Zinc fumes are a health and process consideration	Different fume and joint behaviour; fasteners and sealants must be compatible
Relative cost	Often lower at equal coating mass	Often higher, driven by alloy and process
Best-fit projects	Mild inland roofs, walls, general cladding, cost-sensitive work	Long-life roofing, coastal, industrial and higher-exposure cladding

If your project is inland with low pollution, both can work. If it is coastal, industrial or otherwise aggressive, PPGL is the more common starting specification — but only when the coating mass, paint system and detailing support it.

How to Specify: Substrate, Coating, Paint and Profile

The metallic coating is only one layer. A weak paint system over a heavy metallic coating, or the reverse, will not deliver the performance you expect. Specify all four layers together.

1. Steel substrate

Confirm grade, yield strength, thickness and tolerance. Structural roofing and long-span profiles may need higher strength or tighter thickness control than simple wall cladding. Thickness tolerances affect load capacity and fastener performance.

2. Metallic coating

State the coating type and mass, and the test method. For galvanized material, coating mass is usually quoted in g/m²; for zinc-aluminium, the same convention applies but the alloy differs. Ask whether the figure is per side or both sides combined, and whether it is nominal or minimum. Confirm the required standard edition and exact contract values rather than relying on a generic grade name.

3. Paint system

Common systems include polyester (PE), silicon-modified polyester (SMP), polyvinylidene fluoride (PVDF) and polyurethane, in various thicknesses. Polyester is widely used for general cladding; PVDF is often specified where colour and gloss retention matter over long exposure. State topcoat and primer thickness, back-coat requirement, gloss level, colour tolerance and the test standard for adhesion, impact, bend and salt spray. Remember that salt-spray hours are a comparative laboratory indicator, not a service-life prediction.

4. Profile and detailing

Roof pitch, purlin spacing, rib geometry, end laps, ridge and valley details, and fastener type all influence performance. Dissimilar metals in contact can cause galvanic corrosion; use compatible fasteners, washers and sealants. Cut edges, drilled holes and site-cut sheets should be treated or protected according to the project’s corrosion strategy.

Environment: The Factor Buyers Underestimate

Two identical coils can perform very differently in different locations. Consider:

Distance from the sea and prevailing wind direction, which affect chloride deposition.
Industrial emissions such as sulphur compounds and particulates.
Rainfall and washing: regular rain can help remove deposits; sheltered or unwashed surfaces may accumulate corrosives.
Temperature and thermal cycling, which stress the paint film and fixings.
Contact with soil, concrete, timber or chemicals, which can accelerate attack.
Maintenance access: if inspection and cleaning are difficult, specify more conservatively.

For aggressive environments, a corrosion category assessment — for example using the ISO 9223 framework — can help you align coating and paint choices with exposure. Confirm the required edition and the exact values your contract adopts.

Cost Drivers and How to Compare Quotes

Do not compare PPGL and PPGI on a single price per tonne. Compare on a like-for-like basis, because the following variables change cost significantly:

Steel substrate grade, thickness and tolerance.
Metallic coating type and mass.
Paint chemistry, topcoat and primer thickness, back coat.
Colour, gloss and special finishes.
Coil width, inner diameter, coil weight and tolerance.
Order quantity, delivery terms, packing and documentation.
Testing, certification and third-party inspection requirements.
Market conditions for steel, zinc, aluminium and energy at the time of order.

Because these inputs move, request a dated written quotation that states the specification, quantity, delivery terms, validity period and any price-adjustment mechanism. That is more useful than any indicative figure in an article. If you need to align a specification before pricing, you can contact us with your project details.

RFQ Checklist for PPGL and PPGI Coils

Send this list to every supplier so that offers are genuinely comparable.

Product: PPGL or PPGI, and the intended application (roof, wall, both).
Standard: the standard name, edition and the exact property values required.
Substrate: grade, yield strength, thickness and tolerance.
Metallic coating: type, alloy designation if applicable, mass in g/m², per side or both sides, nominal or minimum.
Paint system: chemistry, primer and topcoat thickness, back coat, gloss, colour reference and tolerance.
Dimensions: coil width, thickness, inner diameter, coil weight range.
Mechanical requirements: bend, impact, adhesion, pencil hardness, if applicable.
Corrosion testing: salt spray or other tests, with method and acceptance criteria.
Surface: finish type (regular, matt, embossed, printed), and any protective film.
Documentation: mill test certificate, coating mass report, paint report, packing list.
Inspection: whether third-party inspection is required, and by whom.
Commercial: quantity, delivery terms, destination, packing, lead-time expectation and quote validity.

Common Mistakes That Cause Disputes

Specifying “PPGL” or “PPGI” without coating mass. The name alone says nothing about corrosion performance.
Mixing per-side and both-sides coating figures. A 100 g/m² figure can mean very different things depending on convention.
Ignoring cut-edge protection. PPGL edges and holes may need extra attention; plan for it before fabrication.
Choosing colour and gloss by eye. Use a defined colour reference and tolerance, and agree on the measurement method.
Assuming salt-spray hours equal years of service. They do not; they are a laboratory comparison under specific conditions.
Forgetting the back coat. The reverse side may be visible or exposed to condensation.
Using incompatible fasteners or flashings. Mixed metals and trapped moisture accelerate corrosion.
Accepting a quote without a specification. If the offer does not state coating mass and paint system, you cannot compare it.
Storing coils poorly. Moisture between wraps can cause white rust or staining before fabrication.
Cutting and forming without protecting edges. Site practice affects performance as much as the coil itself.

Frequently Asked Questions

Is PPGL always better than PPGI for roofing?

No. PPGL is often preferred in aggressive atmospheric environments, but PPGI can be entirely adequate in mild, inland conditions, and it offers stronger sacrificial protection at cut edges. The correct choice depends on exposure, coating mass, paint system, detailing and maintenance.

Can I use PPGL and PPGI on the same building?

It is possible, but be careful about galvanic effects where different metals and coatings meet, especially in the presence of moisture. Confirm compatibility of sheets, flashings, fasteners and sealants with your designer.

How long will a PPGL or PPGI roof last?

There is no single figure. Actual performance depends on substrate, metallic coating type and mass, paint system, environment, forming, fixing details and maintenance. Suppliers may offer indicative guidance, but treat it as conditional and confirm what is guaranteed in your contract.

Does a thicker paint coat compensate for a thinner metallic coating?

Not fully. The paint film is the first barrier, but once it is damaged, the metallic coating governs how the steel responds. Specify both layers to suit the environment rather than trading one against the other.

What coating mass should I ask for?

There is no universal answer. It depends on your exposure category, expected maintenance and design life. Ask your designer or specifier, and require the supplier to state the mass, test method and whether it is nominal or minimum.

Which is easier to form and roll?

Both are routinely roll formed. Success depends on paint flexibility, bend radius, tooling condition and temperature. Confirm the minimum bend radius and run a trial if the profile is complex.

Making the Decision

Start with the environment and the consequences of failure, not with the product name. If exposure is aggressive and long service is expected, PPGL with a suitable coating mass and paint system is usually the more conservative specification. If exposure is mild and cost or cut-edge behaviour dominates, PPGI may be the practical choice. In both cases, the specification — not the label — determines performance.

Write down the substrate, metallic coating, paint system, dimensions, tests and documentation you need. Then ask for a dated quotation against that specification so every offer can be compared on equal terms. If you would like to discuss a PPGL or PPGI requirement for roofing or wall cladding, send your specification and quantity through our contact page and we will respond to the details you provide.