Finishing
Galvanizing vs Powder Coating
Hot-dip galvanizing immerses steel in molten zinc at 450 C, forming a metallurgically bonded 45 to 100 micron sacrificial layer. Powder coating electrostatically applies polymer powder cured at 180 to 200 C into a 60 to 120 micron barrier film. The trade is raw corrosion life against color and finish quality.
| Galvanizing | Powder Coating | |
|---|---|---|
| Protection mechanism | Sacrificial zinc, protects scratches and cut edges | Barrier only; corrosion creeps from chips |
| Coating thickness | 45 to 100 microns, thicker on edges | 60 to 120 microns, thin on edges |
| Service life, C3 outdoor | 40 to 70 years to first maintenance | 10 to 20 years before recoat |
| Applied cost | $0.35 to $0.65 per lb of steel | $2 to $6 per sq ft including prep |
| Appearance | Matte gray spangle, no color options | Any RAL color, gloss to texture |
| Part size limit | Kettle bound, roughly 1.8 x 2.5 x 15 m max | Oven bound, large batch ovens to 3 x 12 m |
| Heat effect on part | 450 C bath can warp gauge under 3 mm | 180 to 200 C cure, minimal distortion |
Choose Galvanizing when
- Outdoor structural steel with a 25+ year life requirement
- Weldments with cut edges, bolt holes, and hidden cavities
- Function-only parts where gray zinc finish is acceptable
Choose Powder Coating when
- Customer-facing parts that need a specific color and gloss
- Thin gauge sheet metal that would warp in a zinc bath
- Indoor or mild-exposure service environments
The verdict
Specify galvanizing for structural steel that lives outdoors 25 years or more; nothing organic matches sacrificial zinc on cut edges and bolt holes. Specify powder coating when the part carries a color or the customer sees it. For coastal or heavy industrial exposure, run duplex: galvanize first, powder coat over it.
Cost comparison
Hot-dip galvanizing prices by weight, typically $0.35 to $0.65 per lb, so a 500 lb weldment runs $175 to $325 with little prep beyond drainage holes. Powder coating the same part costs $250 to $500 including blast and masking, and prices by area, which punishes bulky fabrications. The real crossover is lifecycle: powder needs a recoat at 10 to 20 years outdoors at near full original cost, while galvanizing runs 40+ years maintenance free.
Common questions
Can you powder coat over galvanizing?
Yes, a duplex system is common and extends total life to roughly 1.5x to 2.3x the sum of the individual coatings. The galvanized surface needs a sweep blast or chemical pretreatment plus an outgassing bake near 200 C to prevent pinholes in the powder film.