Leaching of Chromates from Primers Available to Purchase

SEVERE natural exposure and laboratory test, dry salt/humidity, have both shown the advantages of primers that leach chromate over similar primers that do not. This advantage, applicable to both primer only and primer plus finish schemes, is paticularly evident where there are breaks, in the paint film due to edges, damage or paint cracking round rivet heads Several other laboratories have used other tests and have reached the same general conclusions. Sufficient experimental work has been carried out to formulate primers with very different leach rate characteristics. Many of these have been produced and are now being corrosion tested When the results are available it is hoped that they will be sufficiently consistent to enable a leaching test to be included in some paint specifications instead of the present two year corrosion test. Until then it is suggested that this fairly simple test provides a useful means of screening new primers for the paint industry and, for the aircraft constructor, one possible way of chuosing between the several competitive schemes offered to him, without having to wait many years for the results of corrosion lasts.