Coating systems used for anticorrosion protection usually consist of a primer, intermediate layers, and topcoats. Zinc-rich primers, which serve as cathodic and barrier protection, are widely used for the corrosion protection of steel structures. Due to the fact that the functioning of the above-mentioned coatings is related to the conduction of galvanic current, these types of coatings are highly pigmented with zinc (up to 80 wt% in the dry coating). This may result not only in a deterioration of the performance of the coating system but also have a negative impact on the environment. Taking the above into account, solvent-based and water-based organic epoxy primers with zinc content reduced to approximately 50% have been developed. Zinc pigments of different shapes and with different surface treatments were used in the primers, as well as pigments without chemical treatment but with the addition of nanoparticles. It was found that, depending on the type of zinc pigment, both the developed solvent-based and water-based primers demonstrate good protective properties comparable to traditional zinc-rich coatings. Water-based paints tend to absorb more moisture compared to solvent-based systems, but their water uptake reversibility is limited. Moreover, the organic treatment of zinc flakes helps to improve this water uptake reversibility, improving the mechanical properties of coatings.

The durability of coatings is often evaluated by the impact of standardized weathering cycles. While such tests may yield well-differentiated damage patterns, they do not reveal which specific weathering parameters—particularly temperature, moisture, or radiation exposure—contributed to the formation of each observed damage type or to what extent. Consequently, it remains unclear (i) how exactly each individual formulation should be modified in order to optimize coating durability, and (ii) which of the tested coatings are particularly (or less) suitable for specific climatic conditions. In the present study, a testing concept is introduced that is primarily based on conducting single-parameter variants of the fluorescent weathering cycle according to DIN EN ISO 16474-3:A (P1). These variants were designed in such a way that, by comparing the weathering results obtained from sets of three color-identical topcoat systems, conclusions could be drawn regarding the aforementioned aspects (i) and (ii). Indeed, it was demonstrated that formulation modifications derived from the observed results led to a markedly improved weathering stability of the topcoat systems, particularly with respect to their previously identified weaknesses.