For most building panels, the practical answer is this: choose a matte-to-satin finish around 30% gloss at 60° when you want to reduce glare, hide surface waviness and fingerprints, and accept slightly lower reflectivity; choose a semi-gloss finish around 70% gloss at 60° when you want a brighter, more saturated colour and a more reflective architectural look, and you accept that surface defects and oil marks will be more visible. Custom gloss levels are specified when a project has a colour-match, brand-identity or end-use requirement that 30% or 70% cannot satisfy. The final choice is always a contract decision: confirm the gloss value, the measurement geometry, the tolerance band and the test method with your supplier before ordering.
Gloss is not a cosmetic afterthought in prepainted galvanised iron (PPGI). It interacts with paint chemistry, film thickness, curing, forming and weathering. This guide explains what gloss actually measures, how 30% and 70% behave on real buildings, and how to write a specification that your supplier can actually meet.
What “Gloss Level” Actually Means on PPGI
Gloss is a measure of how much light a surface reflects at a defined angle. In coil coating, the number is normally expressed as a percentage of a reference standard measured with a glossmeter.
The 60° geometry is the default reference
Most coil-coating specifications quote gloss at 60° incidence. Some paint systems or automotive-derived specifications also quote 20° (for high-gloss surfaces) or 85° (for matte surfaces). A “30 gloss” and a “70 gloss” are only comparable if both were measured at the same angle with the same instrument type and the same calibration standard. If a quotation says “matte” or “glossy” without a number and an angle, you do not yet have a specification.
Gloss is a paint-system property, not a steel property
The substrate and metallic coating influence appearance indirectly — through surface roughness and through how evenly the paint wets and cures — but the gloss reading itself comes from the topcoat. That means gloss is controlled by resin chemistry, pigment volume concentration, matting agents, film build and oven cure. A supplier cannot simply “polish” a coil to change gloss.
How 30% Gloss Behaves on Building Panels
A 30% gloss finish — often described as matte or satin depending on the supplier’s terminology — is a common choice for roofing and wall cladding where visual calm matters more than shine.
- Lower glare: Large roof areas reflect less sunlight into neighbouring buildings, roads or windows.
- Better tolerance of surface waviness: Diffuse reflection makes minor oil-canning and roll-forming marks less conspicuous than they are on a mirror-like surface.
- Fingerprint and handling marks are less obvious during installation, which can matter on visible façades.
- Colour perception shifts: A matte surface typically appears slightly darker and less saturated than the same colour in a higher gloss, because less specular light reaches the eye.
- Cleaning behaviour differs: Matte surfaces scatter light, so a thin film of dust or chalk may be less visible, but some matte topcoats can be harder to wipe completely clean because of micro-roughness.
Matte systems are widely used in architectural, industrial and infrastructure cladding. Whether a specific 30% product is suitable for a given project depends on the full paint system, not the gloss number alone.
How 70% Gloss Behaves on Building Panels
A 70% gloss finish is a semi-gloss to gloss appearance. It is common where colour impact and a “new” look are priorities.
- Higher colour saturation and depth: Specular reflection makes strong colours — deep blues, reds, greens — appear richer.
- More reflective: Useful in some interior or sheltered applications, but on large roofs it can create glare and heat-related visual discomfort.
- Less forgiving of defects: Dents, scratches, roller marks, oil-canning and uneven film build are more visible because they disrupt a more directional reflection.
- Cleaning and inspection: Smooth, high-gloss surfaces can be easier to wipe, which is relevant for food, pharmaceutical or cleanroom-adjacent cladding — subject to the full coating system being approved for that environment.
Gloss level does not by itself determine weatherability, corrosion resistance or colour retention. Those depend on the resin system (for example polyester, silicon-modified polyester, PVDF), pigment selection, primer, metallic coating mass and the environment.
Decision Table: Matching Gloss to Application
Use this as a starting framework, then confirm exact values in your purchase specification. The “typical gloss range” column is general industry guidance, not a guarantee for any specific product.
| Application / priority | Typical gloss range (60°) | Why it is often chosen | What to confirm in the contract |
|---|---|---|---|
| Large exposed roofs, glare-sensitive sites | Approx. 20–40% (matte/satin) | Reduces reflected glare; hides waviness | Gloss value, angle, tolerance, test method |
| Architectural façades, brand colours | Approx. 30–50% | Balances colour depth with low glare | Colour target and gloss target together |
| General industrial cladding | Approx. 40–70% | Widely available; good colour appearance | Batch-to-batch gloss consistency |
| Interior panels, retail, display | Approx. 60–80%+ | Bright, clean, high-impact look | Scratch and handling protection |
| Colour-critical replacement panels | Match existing | Avoids visible patchwork on a façade | Measured gloss and colour of existing panel |
Where the table says “approx.”, treat the numbers as a conversation starter. Suppliers publish their own standard gloss bands, and those bands are what you should specify against.
Custom Gloss Levels: When 30 or 70 Is Not Enough
Custom gloss is usually requested for one of four reasons:
- Colour matching on a refurbishment. Existing panels may read at, say, 45%, and a 30% or 70% replacement will stand out.
- Brand or design specification. An architect or brand owner may define a precise appearance target.
- Functional requirements. Some end uses need low reflectivity for optical or safety reasons; others need a smoother, more cleanable surface.
- Consistency across multiple suppliers. A single tight gloss band makes it easier to compare quotations.
Custom gloss normally means the paint supplier formulates a specific topcoat. That affects minimum order quantity, lead time, colour-matching effort and sometimes cost. It also means the gloss band should be agreed in writing, with a tolerance, before production. See the product pages for PPGI coil and GI coil for the base material context, and confirm paint-system details with your supplier.
Gloss and the Rest of the Coating System
Gloss cannot be specified in isolation. It sits inside a stack of decisions that together determine appearance and durability.
Substrate and metallic coating
The steel grade, thickness and the zinc or zinc-alloy coating mass affect stiffness, corrosion protection and surface uniformity. A rougher metallic surface can telegraph through the paint and influence measured gloss. Buyers often review galvanised steel coil specifications alongside the paint system.
Pre-treatment and primer
Pre-treatment chemistry and primer adhesion are foundational. Poor adhesion can lead to coating loss regardless of gloss level.
Topcoat chemistry and film thickness
Polyester, silicon-modified polyester, polyurethane and PVDF systems behave differently in colour retention, chalking and gloss retention. Film thickness affects both protection and appearance.
Cure and forming
Under-cure or over-cure changes gloss and flexibility. Aggressive roll forming or bending can crack or mar the coating, and the marks show more on higher-gloss surfaces.
RFQ Checklist for Gloss-Specified PPGI
Include these points in your request for quotation so that offers are comparable:
- Gloss target and measurement angle (for example, “35% ± 5 at 60°”).
- Test method and instrument standard to be used, and whether the supplier or a third party tests.
- Colour target, referenced to a physical sample, RAL or other system, plus acceptable colour difference.
- Paint system type and nominal dry film thickness for primer, topcoat and back coat.
- Substrate grade, thickness and tolerance.
- Metallic coating type and mass per unit area.
- Coil dimensions, inner diameter, coil weight and eye-to-sky or eye-to-wall orientation.
- Surface treatment, if any (for example, protective film type and removability window).
- Mechanical property requirements and forming intent.
- Inspection documents, test certificates and sampling plan.
- Packaging, marking, moisture protection and shipping terms.
- Any standard cited in the contract, with the required edition and exact values confirmed.
If a standard is named — for example a coil-coating, galvanising or test-method standard — ask the supplier to state which edition applies and to confirm the specific acceptance values in the purchase order. Standards are revised, and project specifications sometimes tighten or relax default values.
Common Mistakes When Choosing Gloss
- Specifying “matte” or “glossy” without a number. Words are not measurable; numbers with an angle and tolerance are.
- Mixing measurement angles. A 70% reading at 60° is not the same appearance as a 70% reading at 20°.
- Assuming gloss equals durability. Gloss retention and corrosion performance depend on the whole system and the environment.
- Ignoring batch variation. Even within a band, gloss can drift between production runs. Ask how consistency is controlled.
- Forgetting forming. Tight bends and severe profiling can damage any coating; higher gloss makes damage more visible.
- Comparing quotes on gloss alone. Two “30 gloss” offers may differ in paint chemistry, film thickness and metallic coating.
- Overlooking the back coat. The reverse side is often a different colour and gloss; confirm it if the panel edge or underside is visible.
Cost Drivers and Quotation Notes
Gloss level itself is rarely the main cost driver, but it can influence cost through:
- Paint formulation complexity, especially for custom or tightly toleranced gloss.
- Minimum order quantity for a custom topcoat.
- Colour-matching and sample approval effort.
- Production scheduling and changeover.
- Testing and documentation requirements.
Because paint, zinc, steel and freight markets move, a meaningful price must be tied to a date, a specification and a quantity. Request a dated written quotation that lists the gloss value, angle, tolerance, paint system, film thickness, substrate, metallic coating mass and delivery terms. Avoid comparing offers that omit these details.
FAQs
Is 30% gloss the same as matte?
Suppliers use “matte”, “satin” and “low gloss” differently. A 30% reading at 60° is generally in the low-gloss range, but the appearance also depends on the paint system and surface texture. Always specify the number and angle rather than relying on the label.
Does a higher gloss coating last longer?
Not automatically. Gloss retention, chalking and corrosion resistance depend on the resin system, pigments, film thickness, metallic coating, environment, forming and maintenance. Do not assume that a 70% gloss product will outperform a 30% product on service life.
Can I get the same colour in both 30% and 70% gloss?
Often yes, but the perceived colour will differ. Matte surfaces typically look slightly darker and less saturated. If colour matching is critical, approve physical samples in the intended gloss.
How is gloss tested on a coil?
Typically with a glossmeter on a prepared flat sample, at a defined angle, following an agreed test method. Confirm whether the supplier tests at the coil line, on a laboratory panel, or both, and how often.
What tolerance should I specify?
There is no universal answer. Many specifications use a band around a target, but the acceptable width depends on the application and the supplier’s capability. Agree the band in writing before production.
Can gloss change after installation?
Yes. Weathering, chalking, dirt accumulation, cleaning agents and mechanical damage can all change measured gloss over time. The rate and extent depend on the coating system, the environment, installation quality and maintenance regime.
Next Step: Define the Spec, Then Ask
Write down four things before you contact any supplier: the gloss value and angle, the acceptable tolerance, the colour target, and the full coating system. Then request a dated quotation against that specification so offers can be compared fairly. If you need help structuring a PPGI or GI coil enquiry, you can send your requirements to ChinaCNU Steel and ask for a written quotation with the gloss, paint system and test details stated explicitly.
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