La peinture sur substrats rouillés

Painting on rusted substrate

Directeur du Laboratoire de tropicalisation de l’Office de Recherche Scientifique et Technique Outre-Mer (ORSTOM) (en retraite)

Abstract

Painting on rusted surfaces is generally not recommended. Anyhow, for some reasons, it remains difficult to avoid it completely. Keeping this in view, we studied the behaviour of rusted plates covered with various systems under naturel exposure or under accelerated salt-spray testing for corrosion.

The paint systems were specially fitte dones, for use before painting on rusted surfaces, or more classical systems. The first ones apparently did not furnish the expected results, so far the general aspect of the surface is concerned.

To make the point clear, the penetration into the rust has been measured on cross sections included into resin and polished before examination under the microscope. Corrosion products evolution under the paint has been followed using semi-quantitative analysis with X ray diffraction.

From this all, it can be concluded that the rust must not be thicker than 50 μ to have some chance for the rust stabilizer to reach the metal, and that no marked change occurs in rust, which can be put on the account of the products.

Apart o f this, classical systems like those based on lead metal or zinc chromate pigments look more attractive. They stand better and call for recommendation in such conditions.