Effect of variable amounts of rust at the steel/paint interface on the behaviour of anticorrosive paint systems

This paper analyses the effect of the presence of rust at the metal/paint interface on the behaviour of different paint systems used for protecting the structural steel exposed to the atmosphere. The paint systems were applied as films of variable thickness over rusted steel surfaces cleaned to different grades of surface preparation (Sa3, Sa2(1/2), Sa2 and SO). Pre-rusting of steel was carried out in a clean (uncontaminated) rural atmosphere. Atmospheric exposure tests were conducted for 14 years at three Spanish test sites of different atmospheric corrosivity. Exposed specimens were evaluated for rusting and blistering, as well as for delamination of the paint system on both sides of a scribe made in the paint film. The results reveal that in some cases the presence of rust has a negligible influence on the durability of the paint system applied. Those systems including a zinc-rich (ethyl silicate) primer were found to provide the most effective protection against corrosion under all types of conditions tested. (C) 2002 Elsevier Science B.V. All rights reserved.