Zinc rich primers are extensively used for corrosion protection in the marine and protective industry. During the 60’s/70’s zinc rich epoxy (organic) primers were dominating the market. Later zinc ethyl silicate (inorganic) primers took over this role but nowadays it looks as if zinc epoxy primers have made a comeback. Some of the advantages of zinc epoxies compared to zinc silicates are the less demanding curing conditions (epoxies will cure at low humidity), they are easier to overcoat and they are less demanding to substrate preparation prior to application. The latest trend from the Owners and Fabricators is to improve the constructability and productivity on their works; this is a key benefit where the organic outperformed the inorganic being this translated into improve efficient, throughput and at the end of the day savings millions of dollars. Zinc epoxies are typically formulated with high loads of zinc dust. According to ISO 129448 a zinc rich coating contains more than 80% zinc by weight in the dry film.
The protecting mechanism of zinc rich coatings is believed mainly to be based on cathodic protection provided by the zinc dust in the paint. When a coating system containing a rich primer is exposed, rust creep and blistering are the most important failure mechanism to be considered.
The increasing demands to the performance of zinc rich primers (low rust creep) has addressed even more focus on maximizing the utilization of the zinc dust in the paint. Is it possible to achieve the same cathodic protection with a lower content of zinc dust ?
The purpose of this paper is to describe the protecting mechanisms of a new generation of zinc rich primers with enhanced protection and mechanical properties and to set up the design criteria for a well working system. Results from different corrosion tests (ISO 129448 ; NORSOK M5019, Rev.6) and mechanical experiments are presented.