full-scale trials of ten paint systems, applied on the plate girders of the loudwater viaduct, are described. a general conclusion is that aluminium pigment should be excluded from conventional micaceous iron oxide paints. in several instances aluminium has been leached out as aluminium salts leading to deterioration of the paint system and rusting of the substrate. the best performance after four years of exposure is given by a solventless epoxy system, but its application requirements were stringent and may be difficult to meet in practice. for high corrosivity sites, a chlorinated rubber paint system should give a good performance with easy application, although transportation damage between fabrication shop and site may be a problem. the importance of the micro-climate to which sheltered bridge steel work is exposed is discussed. steel girders are not washed by rain and the combination of corrosive contaminants and long periods of wetness can be a particularly severe condition for paint coatings under a bridge deck. further research on the characterisation of bridge sites and evaluation of priming paints has been initiated.(a) (paper given to a symposium on developments in steel highway bridge protection held at trrl, 7th nov.1972.)

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