The use of zinc in paints to provide corrosion protection has been around for over 100 years. However, its effectiveness and use in the past five decades has increased dramatically, due to ongoing research and development. Zinc-rich paints provide exceptional corrosion protection and are used in various industrial and marine settings. Their use can be found in heavy steel applications such as bridges, barges, pipelines – any steel based construction where corrosion protection is critical.
There are two basic ways to classify zinc coatings. One is based on the amount of zinc the coating contains. Zinc-rich primers contain 80 wt% of zinc in the cured paint film. In these primers, the only active pigment is the zinc powder. The second classification is known more simply as a zinc primer. These contain less zinc pigment, in the range of 25-70%. These are most commonly used in fabrication shops, or for the protection of stored steel on a temporary basis. The zinc-rich primers are used for lasting corrosion protection in steel structures. Zinc coatings may also be referred to as organic or inorganic, depending upon their chemical makeup. They are available in formulations that are low in volatile organic compounds (environmentally friendly).
Zinc-rich primers are effective because they provide protection in several different ways. The most obvious is the barrier they provide, which is not unique to zinc-rich primers. All coatings provide some level of barrier protection. Zinc-rich primers also provide protection through galvanic or cathodic mechanisms. The coating sacrifices itself (much like an anode would do) and corrodes instead of the iron or steel it is protecting. Only the zinc-rich coatings provide this level of protection. The third reason zinc protects is that as it corrodes it produces by-products (zinc hydroxides, zinc hydroxy carbonates) that add another protective barrier. As the by-products build up they create this secondary seal or barrier of protection. Finally these same by-products will increase the alkalinity of the coating, and steel corrodes less rapidly in an alkaline environment.
If you have a need for a corrosion resistant coating, and you need superior corrosion control, you will want to consider the benefits and superior protection zinc coatings have to offer.