Alternatives to galvanizing and powder coating

For buildings and building components made of steel, such as balconies, railings or carports, the surface coating of the components plays an important role. On the one hand, it is meant to add visual accents, and on the other hand, to protect the components against environmental influences and corrosion for as long as possible. In structural steelwork with mild steel, three types of surface finishing are mainly used:

• Painting
• Galvanizing
• Powder coating

Painting and powder coating provide corrosion protection by keeping oxygen away from the component surface. With galvanized components, corrosion protection is additionally achieved through electrochemical protection, which also works at defects such as surface cracks. You can find details in this article on galvanizing.

Better corrosion protection by combining the processes

If you want the components to be coloured but do not want to give up the cathodic corrosion protection of galvanizing, the processes can be combined: the components are first galvanized and then coated with wet paint or powder coating.

This gives you double corrosion protection that withstands severe environmental influences.

Drawbacks of galvanizing and coating

However, combining the processes does not only have advantages; it also has drawbacks:

Time-consuming preparation

Galvanized components cannot be coated directly. Galvanizing can leave rough spots, pimples or flaking in the zinc layer. These spots must be laboriously cleaned and reworked.

Dimensional accuracy

In galvanizing, the components are dipped into a bath of molten zinc. The resulting surface is not equally thick everywhere. Where the zinc cannot drain off well, thickened areas form, while in other places the zinc layer may be thinner.

Component geometry

For hot-dip galvanizing, the components must be designed so that the molten zinc can reach every part of the component and drain off again. Where this is not possible, suitable holes must be provided. Depending on the application, these holes may be considered undesirable.

Costs

The additional cost of galvanizing is approx. 0.40 €/kg. On top of this come transport costs and the cost of preparing the zinc layer for coating. As a rule, the combination of galvanizing and coating is more than twice as expensive as coating alone.

Higher corrosion resistance without galvanizing

A few years ago, the Max Planck Society developed an alternative to galvanizing and coating. Inspired by the self-healing powers of human skin, a coating was developed that repairs defects by itself. For this purpose, so-called “smart pigments” are embedded in the coating. When defects or cracks occur, these tiny containers release a corrosion inhibitor that closes the surface again.

Last revised on 22 April 2021 by Andreas Janisch