Post-galvanizing

Although galvanized steel's look is increasingly popular, including for residential applications, you often still need to paint galvanized steel. Thankfully, this is a popular practice, and its technique is usually mastered by paint professionals.

Here is an overview of what needs to be followed for post-galvanizing painting. The following content addresses surface preparation when painting galvanized steel.

Why paint?

The first answer that comes to mind is "for the look"! Paint can simply be required by the architect, but it can also be used for identification purposes or as extra protection in a harsh environment. Painting galvanized steel is known as a duplex system.

The benefits are...

• Paint acts as an additional barrier protecting galvanized steel;
• Galvanizing’s corrosion protection properties are enhanced and optimized by applying paint;
• Paint scaling is reduced due to the underlying galvanized steel;
• Together, galvanizing and paint offer longer-lasting surface protection;
• Combined service life is 1.5 to 2.5 times their individual service life.

Galvanized steel goes through an oxidation (or aging) process that is illustrated with the help of what is called the "passivation cycle."

When should paint be applied?

Galvanized steel has three (3) “aging stages” (when oxides are present) and paint can be applied at any stage, provided that there is proper surface preparation…

• Immediately after the galvanizing treatment
• When the galvanized steel is at 50% of its service life
• When the thickness of the galvanized sheet is ≤1mils
• At the first sign of rust spots