Performance of Maintenance Coatings Applied on Rusty Steel Surfaces

The effect of climate conditions during application and curing of repair coating systems performance has been investigated. Pre-rusted steel panels cleaned by UHP water jetting, blast cleaning and mechanical grinding have been used as substrates. Performance of various repair coating systems with respect to corrosion protection and adhesion have been reported earlier. Surprisingly the test panels cleaned with a rotating steel brush were among the best in the test. Steel brushing removes less surface rust and salt contamination compared to blast cleaning and UHP water jetting, and rather poor results were therefore expected. Mechanical grinding pre-treatment methods using 3M disc and rotating steel brush were compared in a new test program. Ageing resistance testing showed less corrosion creep from scribe for steel brushed panels than for panels pre-treated by purple 3M disc, in spite of the presence of an almost continuous film of rust on the steel brushed surface. Electrochemical characterisation of cleaned panels showed a more positive corrosion potential for the steel brushed panels. This is probably due to a corrosion protection effect by the rust present on the surface of these samples.