Aesthetics are important to nearly every construction project. Whether an attractive, artfully designed sculpture or architecturally exposed steel element, bridge, bus station, or other infrastructure element, galvanized steel offers design flexibility, and an attractive, natural gray finish.
The natural, matte gray finish does not suit every project of every specifier – as sometimes color is preferred or needed for branding, safety marking, etc. However, by specifying a duplex system – galvanizing your project and then painting or powder coating over to the desired color ensures you don’t have to sacrifice the corrosion protection benefits and extended maintenance of HDG steel.
Duplex systems provide more benefit than just aesthetic options. The combination of hot-dip galvanized steel and paint or powder coating provide a synergistic effect. The paint/powder extends the life of the coating by providing an additional barrier coating to the zinc layers, while the galvanized steel prolongs the life of the paint coating by preventing underfilm corrosion and peeling.
The result of the two coatings working in synergy is extended corrosion protection. The service life of a duplex system is 1.5 to 2.3 times the sum of the individual systems. For example, if the life of the galvanized coating in a particular environment is 70 years, and the expected life of the paint is 10 years, the expected life of the duplex system would be at least 120 years (1.5 x (70+10)).
This extended service life assumes no maintenance will be done to keep the paint or powder coating intact. Realistically, if someone invests the premium cost upfront for a duplex system, they likely plan to keep the color on the structure. So, in practical terms, the synergistic effect of utilizing a duplex system is the extended maintenance cycle it provides. With hot-dip galvanized steel as a “primer,” the time to first maintenance of the paint or powder coating is extended 1.5 to 2.0 times what it would be for bare steel. The AGA’s publication Duplex Systems: Painting Over Hot- Dip Galvanized Steel and instructional DVD guide Preparing HDG Steel for Paint provide more information on specifying duplex systems.