Why is it some galvanized coatings have a dull, gray finish, while others have a bright, shiny finish? Also, which coating provides better corrosion protection? It is true the galvanizing process is similar for most steel galvanized; however, there are several variables that affect the galvanizing process and determine product quality.

As stated, the appearance of hot-dip galvanized steel immediately after galvanizing can be bright and shiny, spangled, matte gray, or a combination of these. There are two elements of steel chemistry which most strongly influence the final appearance; silicon and phosphorous.

The shiny section of guardrail on the right side of the top picture was galvanized and stored under cover while exposed to freely-flowing air. Both were galvanized in the same batch. The right photo depicts the same guardrail sections 3½ months after they were first attached to the concrete barrier.

Some appearance issues on galvanized coatings occur more frequently, such as mottling, dull and shiny parts on the same fabrication, bare spots, inclusions (various types), and flaking or delamination of the galvanized coating.

Reactive steels tend to produce thicker galvanized coatings with a matte gray appearance instead of the typical shiny appearance. This difference in appearance is a result of the rapid zinc-iron inter-metallic growth that consumes all of the pure zinc layer (the growth of the inter-metallic layer is out of the galvanizers control).