- Powder is commonly about 60–120 μm and provides color plus barrier protection.
- Zinc electroplate is often about 5–25 μm and suits smaller, dimension-sensitive parts.
- Hot-dip zinc is commonly about 45–85 μm and requires vented/drained geometry.
- Salt-spray hours cannot be converted directly to outdoor life.
Values in this guide are practical starting points for RFQ, DFM and prototype validation. They do not replace load calculations, regulations, material certificates, qualified procedures or approved production drawings.
Start with Typical Thickness and Dimensional Effect
Typical single-coat powder film is about 60–120 μm. Electroplated zinc is often specified around 5–25 μm depending on service class and conversion finish. Fabricated hot-dip galvanized steel commonly has minimum mean coating requirements in roughly the 45–85 μm range depending on steel thickness and governing standard. These are typical ranges, not universal defaults. Define masking, post-machining or allowance at fits, threads, slip joints and grounding faces.
Powder Coating: Appearance and Barrier Protection
Powder offers color, texture and batch appearance. Weak points include reduced coverage on sharp edges, substrate exposure after damage and weatherability that depends on resin chemistry. Epoxy/polyester hybrids may suit interiors; durable polyester or higher-performance systems should be evaluated for long outdoor exposure. Define degreasing and conversion/abrasive preparation. Extra film thickness does not compensate for rust, scale, spatter or poor pretreatment.
Zinc Plating: Thin Coating for Smaller Hardware
Zinc plating suits small brackets, stampings and fasteners and may use clear/blue or black trivalent passivation; color is not a performance class. Deep recesses and blind geometry may receive less coating because of current distribution. High-strength steel requires hydrogen-embrittlement review. ASTM B633 does not recommend zinc electroplating steels above 1700 MPa tensile strength under that specification; fasteners also require their dedicated coating standard and appropriate hydrogen-relief controls.
Hot-dip Galvanizing: Robust Outdoors, Geometry-dependent
The completed fabrication is immersed in a zinc bath near 450°C, coating accessible inside and outside surfaces. It suits rails, frames and outdoor structures. Hollow sections need adequate vent and drain holes to prevent trapped pressure and zinc. Large thin panels and asymmetric weldments can distort. Spangle, runs and local roughness are process characteristics, so cosmetic expectations need an approved reference.
How to Specify and Inspect
Specify substrate, pretreatment, coating standard, thickness and measurement locations, cosmetic zones, adhesion and repair method. ISO 9227 salt spray is a controlled accelerated comparison, not a conversion from hours to outdoor years, and it cannot replace exposure and drainage assessment.
QUICK COMPARISON
Indoor colored cosmetic part: powder coating.
Small hardware, thin film and dimension-sensitive features: zinc plating.
Long-term outdoor steel with acceptable industrial appearance: hot-dip galvanizing.
High protection plus color: evaluate a hot-dip galvanized duplex coating system.
REFERENCES
ISO 1461:2022 (hot-dip galvanized coatings on fabricated articles), ISO 2081 or ASTM B633 (electroplated zinc), the ISO 12944 series (protective coatings for steel structures), and ISO 9227 (salt-spray testing).