Zinc primers vs. galvanizing, the age-old debate
Inorganic zinc vs. galvanized coating applications
The following information was derived from the NACE Publication; “Corrosion Prevention by Protective Coatings” by Charles Munger; p: 153.
There is an age-old debate regarding using inorganic zinc primers versus galvanizing steel for protection against corrosion in exterior environments.
Inorganic zinc coatings contain metal, but they’re considered a silicate coating rather than a metallic coating like galvanized zinc. Galvanized coatings bond to the application’s surface with an amalgam of zinc and iron, while inorganic zinc coatings use iron and silica.
Inorganic zinc coatings are made up of individual zinc particles surrounded and interlocked by a zinc-silicate matrix that is only reactive to strong acids or alkalis, giving it a long lifespan under most environmental conditions. Galvanized zinc coatings are much more reactive to acids in the atmosphere, generally causing a briefer lifespan.
Studies found hot dip galvanized panels exposed to two years of tidal conditions were almost completely broken down by pinpoint rust. The panels coated with 3 mils of an inorganic zinc coating showed no substantial corrosion.
Inorganic zinc coatings are ideal for industries like marine operations, because they can provide protection with only a single thin application that’s less electrically conductive than galvanized zinc. The rock-like matrix of zinc silicates makes these coatings abrasion resistant, while galvanized coatings have a more malleable surface.