⚪ White Rust
In humid conditions, galvanised steel develops a white powder (zinc oxide). It must be cleaned with a nylon brush and water before any painting.
Painting Galvanised Surfaces
Preparation and painting guide for galvanised steel without peeling.
Why does paint peel off galvanised steel?
Galvanised metal (steel coated with zinc) is extremely durable, but it's a "painter's nightmare." The smooth zinc surface and the chemical reaction of oil-based paints with the metal (saponification) lead to total paint failure and peeling within months.
⚠️ Warning: Tools
Do not use wire brushes! They destroy the protective zinc patina. Only use mild abrasive means for cleaning.
Preparation: Degreasing and Etching
New galvanised metals have a layer of oil (passivation) from the factory. If not removed, the paint will fail 100%.
- Degreasing: Thorough cleaning with nitro thinner or a strong degreaser.
- Chemical Etching: Use of a weak acid (like white vinegar for DIY) to create micro-roughness.
- Drying: The surface must be completely dry before priming.
Wash Primer or Epoxy Primer?
Never apply oil-based paint directly to bare galvanised steel. You need an adhesion "bridge":
🧪 Wash Primer (2K)
The "gold standard." It contains special acids that chemically "bite" the surface (self-etching), ensuring perfect adhesion in no time.
🛡️ Epoxy Primer (2K)
The solution for industrial environments. It creates a thick, impermeable film but requires light mechanical abrasion (sweep blasting) to adhere properly.
📐 Engineering Rule: Adhesion failure on galvanised steel is usually due to the saponification of alkyd resins. Always use a primer that chemically isolates the topcoat from the zinc.
Duplex Systems (ISO 12944-5)
The combination of galvanising and painting is called a Duplex System. The result is synergistic: the paint protects the zinc, and the zinc prevents corrosion under the paint.
The lifespan of a Duplex system is 1.5 to 2.3 times longer than the sum of the durability of the two methods separately, often reaching a century without maintenance.
Related Articles
Aluminium: Preparation and Adhesion Metal Primers: Which and When? Surface Preparation Before Painting
Metal Painting & Anti-Corrosion Protection
Return to category.
Go to categoryCentral Guide
Return to the central guide.
Go to guidePaint Guide
Return to the main metal painting guide.
View moreTechnical Support
Need a professional specification for a Duplex system?
Contact us