Deterioration of paint systems applied on zinc substrates contaminated with soluble salts

The presence of soluble salts at the metal/paint interface is one of the main reasons that cause the premature deterioration of the painted metallic structures. This is specially important in the case of zinc substrates due to the increasing amount of galvanised structures that are painted after weathering (duplex system: galvanising+paint). Nevertheless, most of the studies to quantify the tolerable levels of soluble salts for different organic coatings have been carried out with steel substrates. In this paper, the behaviour of some organic coatings applied over pure zinc contaminated with different levels of chlorides and sulphates is analysed. Tests were conducted in the atmosphere as well as in the accelerated humidity condensation cabinet.