If you are sourcing roofing sheet, wall panels or appliance casings, you will meet the term PPGI on almost every quotation. This guide explains what PPGI is, how it is made and how to specify it for your project.
What Is PPGI?
PPGI stands for pre-painted galvanized iron. In practice, it means pre-painted galvanized steel. A galvanized steel coil is cleaned, chemically treated and coated with paint on a continuous line, then baked. The coil is painted before it is cut and formed, which is why it is called “pre-painted”.
You will also see PPGI called color coated steel, prepainted steel or coil coated steel. They describe the same product.
The value of PPGI is simple. The zinc layer protects the steel, and the paint protects the zinc. The end user gets a finished, colored surface with no painting on site.
How PPGI Is Made
PPGI is produced on a continuous color coating line. The main steps are:
- Uncoiling and joining: Galvanized coils are joined end to end, so the line runs without stopping.
- Cleaning: Alkaline cleaning removes oil and dirt from the zinc surface.
- Pretreatment: A chemical conversion layer helps the paint bond to the zinc.
- Primer coating: Rollers apply a primer to the top and a back coat to the reverse side.
- First curing: The strip passes through an oven to bake the primer.
- Finish coating: Rollers apply the colored top coat.
- Final curing and cooling: A second oven cures the top coat, then the strip is cooled.
- Recoiling: The coil is rewound, often with a protective film on the top surface.
The result is usually called a “2/1” or “2/2” coating. The first number is the coats on the top side. The second is the coats on the back.
Structure of a PPGI Sheet
A cross-section of PPGI shows several layers, from the outside in:
| Layer | Typical thickness | Purpose |
|---|---|---|
| Top coat | 15–20 µm | Color, gloss, UV and weather resistance |
| Primer | 5–7 µm | Adhesion and corrosion resistance |
| Pretreatment | Under 1 µm | Bonds paint to zinc |
| Zinc coating | 7–20 µm per side | Sacrificial protection of the steel |
| Steel substrate | Usually 0.12–1.2 mm | Strength and formability |
| Back coat | 5–10 µm | Protects the reverse side |
These are common industry ranges. Your order should state the exact values you need.
PPGI Paint Types
The top coat decides how the color holds up in sunlight and weather. Four paint systems cover most orders:
| Paint system | Main strengths | Typical use |
|---|---|---|
| PE (polyester) | Good color range, flexible, economical | Most roofing, cladding and appliance work |
| SMP (silicone-modified polyester) | Better gloss and chalk resistance than PE | Roofing and walls in strong sunlight |
| HDP (high-durability polyester) | Strong UV and color stability | Long-life roofing and cladding |
| PVDF (polyvinylidene fluoride) | Best fade and chemical resistance | Architectural facades, coastal and industrial sites |
PE is the default for most projects, and it is the most economical choice. Move up to SMP or HDP when the color must stay bright for many years in strong sun. Choose PVDF for landmark facades or harsh coastal and chemical environments.
Colors are usually matched to RAL codes. You can also choose gloss level and special finishes, such as matt, wrinkle or printed wood grain patterns.
PPGI vs PPGL: What Is the Difference?
The difference is the metal coating under the paint.
- PPGI uses a zinc coating (galvanized steel).
- PPGL uses an aluminum-zinc coating, often called Galvalume or AZ.
Aluminum-zinc coatings usually give better barrier protection in many outdoor environments. Zinc coatings give stronger sacrificial protection at cut edges and scratches. PPGI also forms well and is widely available in many sizes and colors.
For most roofing, wall cladding and appliance work, PPGI is the standard choice. Your project specification or local building code decides which one is required.
Where PPGI Is Used
PPGI turns up across construction and manufacturing:
- Building envelopes: Corrugated and trapezoidal roofing sheets, wall cladding and roof tiles.
- Sandwich panels: Facings for insulated panels in cold rooms, warehouses and clean rooms.
- Home appliances: Side panels for refrigerators, washing machines and air conditioners.
- Doors and partitions: Garage doors, roller shutters and interior partition walls.
- Ducting and enclosures: Ventilation ducts, electrical cabinets and equipment housings.
Each use needs a different balance of formability, paint system and zinc coating. A roofing sheet needs weather resistance. An appliance panel needs a smooth, flexible coating that survives deep bending.
How to Specify PPGI in Your Order
Most PPGI disputes come from unclear orders, not from bad material. List these points in every inquiry:
- Base steel grade: For example, DX51D for general forming, or a structural grade for load-bearing profiles.
- Thickness basis: Base metal thickness (BMT) or total coated thickness (TCT).
- Zinc coating: For example, Z80, Z120 or Z275.
- Paint system and thickness: For example, PE, 20 µm top and 7 µm back.
- Color and gloss: RAL code, gloss level, or a physical color sample.
- Width, coil ID and coil weight: Or sheet length if you need cut sheets.
- Protective film and packing: Film type, and whether coils ship eye-to-wall or eye-to-sky.
The thickness basis deserves special attention. A sheet sold as “0.5 mm” may be 0.5 mm of steel, or 0.5 mm including paint and zinc. The difference is about 0.03–0.05 mm. On a large roofing order, that changes both strength and the number of square meters per tonne.
The zinc coating under the paint is easy to overlook. A thin zinc layer keeps the price low, but it shortens life once the paint is scratched. For long-life roofing or coastal sites, a heavier zinc coating is worth the extra cost. Our article Galvanized Coating Thickness: Z275, G90 and How to Choose explains how to read coating weights.
PPGI Coil or PPGI Sheet?
Choose PPGI coil if you run your own roll forming, slitting or panel line. Coils give you the lowest material cost and the most flexibility on length.
Choose PPGI sheet if you need flat, cut-to-length pieces ready for fabrication. You avoid the investment in decoiling and cutting equipment.
Both start from the same galvanized steel coil. The choice depends on your production setup.
FAQ
What Does PPGI Stand For?
PPGI stands for pre-painted galvanized iron. The base material is actually galvanized steel, not iron. The name comes from older trade use and is still standard on quotations and shipping documents. You may also see it written as prepainted galvanized steel or color coated galvanized steel. All of these terms describe the same product.
Is PPGI the Same as Color Coated Steel?
In most cases, yes. PPGI, color coated steel and prepainted steel usually describe painted galvanized steel. Strictly speaking, “color coated steel” can also cover other substrates. PPGL uses an aluminum-zinc base, and some color coated steel uses a cold rolled base. Check the substrate on the quotation, not just the product name.
How Long Does PPGI Roofing Last?
It depends on the paint system, the zinc coating and the climate. A PE system on a light zinc coating suits mild inland conditions. SMP, HDP or PVDF paint over heavier zinc extends service life considerably. Coastal air, industrial pollution and strong sunlight shorten it. Correct fixing and drainage also protect the coating at laps and cut edges.
What Is the Difference Between PPGI and Galvanized Steel?
Galvanized steel has only a zinc coating. PPGI adds pretreatment, primer and a colored top coat on top of that zinc. The paint gives a second barrier against corrosion and a finished color. So PPGI needs no painting after installation. Plain galvanized steel suits parts that will be painted later or hidden from view.
Can PPGI Be Welded?
PPGI is not normally welded. Welding heat burns the paint and the zinc around the joint, which leaves an unprotected area. Roofing and cladding are joined with self-drilling screws, rivets, seaming or clinching instead. If a part must be welded, plain galvanized steel painted after fabrication is usually the better choice.
What Is the Most Common PPGI Thickness?
Thin gauges dominate roofing and cladding, often between 0.3 mm and 0.6 mm. Sandwich panel facings and appliance panels use similar or slightly thicker sheet. Thicker material is chosen for longer spans and higher wind loads. Always state whether the thickness is base metal thickness (BMT) or total coated thickness (TCT).
Conclusion
PPGI gives you galvanized protection and a finished color in one material. The right paint system, zinc coating and thickness basis decide how long it lasts. We process PPGI coil and sheet in Wuxi and cut it to your length. Send us your specification and color code for a quote.