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When sourcing galvanized steel, one of the most important specifications is the zinc coating weight. This figure—often expressed as a designation like Z100, Z180, or Z275—directly determines the product's corrosion resistance and service life, especially in outdoor or aggressive environments. This article explains what coating designations mean, common standards, and how to select the appropriate coating for your needs.
Coating weight is the total weight of zinc applied to both surfaces of the steel sheet, expressed in grams per square meter (g/m²). The "Z" designation stands for zinc. For example, Z100 indicates a minimum total coating weight of 100 g/m² on both sides, which translates to approximately 7 microns of coating thickness per side (using the conversion: 1 µm ≈ 7.14 g/m² for pure zinc).
Designations are defined by international standards:
| Standard | Coating Designation (Examples) | Coating Weight (g/m², both sides) |
|---|---|---|
| ASTM A653 (US) | G60, G90, G115, G185 | 60, 90, 115, 185 |
| JIS G3302 (Japan) | Z12, Z18, Z27, Z35, Z45 | 120, 180, 270, 350, 450 |
| EN 10346 (Europe) | Z100, Z140, Z200, Z275, Z350 | 100, 140, 200, 275, 350 |
Note: Approximate conversions: Z60 ≈ G30, Z100 ≈ G60, Z275 ≈ G90.
| Designation | Total Coating Weight (g/m²) | Approx. Thickness per Side (µm) | Recommended Environment |
|---|---|---|---|
| Z60 | 60 | 4 | Dry indoor, low humidity |
| Z80 | 80 | 6 | Indoor general use |
| Z100 | 100 | 7 | Indoor and mild outdoor |
| Z120 | 120 | 8 | Standard indoor/outdoor |
| Z180 | 180 | 13 | Outdoor, rural atmosphere |
| Z275 | 275 | 20 | Standard outdoor construction, roofing, structural |
| Z350 | 350 | 25 | Heavy industrial, marine, coastal |
| Z450+ | 450+ | 32+ | Severe marine, high humidity, aggressive environments |
The table below provides general guidelines for selecting coating weight based on service conditions:
| Environment | Recommended Coating (Minimum) | Typical Service Life Expectancy |
|---|---|---|
| Dry indoor (office, warehouse) | Z80 – Z100 | 25–50+ years |
| Standard outdoor (rural, mild urban) | Z180 – Z275 | 25–75+ years |
| Industrial, heavy urban | Z275 – Z350 | 20–50+ years |
| Marine coastal, high humidity | Z350+ (or Zn-Al coating) | 15–40+ years |
| High temperature / wet conditions (>65°C water) | Consult with specialist; use Zn-Al or specially formulated coatings | Varies |
Coating Weight vs. Thickness: For the same coating designation, thickness may vary slightly between standards due to different testing methods (e.g., triple-spot vs. single-spot tests). Always refer to the specific standard for exact requirements.
Edge Protection: Heavier coatings provide better edge protection. For cut edges in corrosive environments, consider specifying a higher coating weight.
Formability: Very heavy coatings (e.g., Z350+) may be more susceptible to cracking during severe forming (e.g., bending or stamping). Consult your supplier for specific grade recommendations.
Cost vs. Performance: Heavier coatings increase material cost, but may extend service life significantly, reducing long-term maintenance or replacement costs.
The coating weight can also influence the spangle (crystal) pattern. Heavier coatings may exhibit larger spangles, while lighter coatings or zero-spangle products offer a smoother, more uniform surface—preferred for painting.
For zero-spangle galvanized steel, we can produce coils with thicknesses 0.2–0.8 mm, widths 700–1250 mm, and coating weights ranging from 30 to 180 g/m² (Z30–Z180), with various surface treatments including chromate-free passivation and anti-fingerprint. Visit our product page or contact us to discuss your specific requirements.
