The effects of soluble salts at the metal/paint interface: advances in knowledge

Abstract

The presence of soluble salts (particularly sulphates and chlorides) at the metal/paint interface is known to have a detrimental effect on the integrity of most paint systems. Though this is a long-standing problem, it has recently come to receive greater attention from the protective coatings industry. International Standards Organization (ISO) has for some time been trying to develop a standard about guidance levels for water-soluble salt contamination before the application of paints and related products. In the paper the following points are reviewed: degradation mechanisms, nature and sources of soluble salts, their distribution on the metallic surface, the joint action of chlorides and sulphates, the effect of the joint presence of rust, new methodologies for sample preparation with known levels of soluble salts, measuring soluble salts, establishment of threshold levels, removal of salts and new suitable coating systems for applying on substrates contaminated with soluble salts.