Thick coating compositions

A coating composition especially suitable for a machinable aluminum-filled thick coating possessing improved salt corrosion and oxidation resistance, which composition comprises a liquid binder which comprises phosphate ions and ions of the group of chromate or molybdate ions, and an atomized aluminum powder having a particle size distribution curve containing two peak frequencies which are attributable to the presence of a mixture of larger particle size powder having an average particle size greater than 15 .mu.m in which the size distribution is such that at least about 5% by weight of the particles is retained on a 325 mesh screen and at most 50 weight percent of a mixture of smaller particle size powder, the two powders being in such ratio that the average particle size, medium equivalent spherical diameter (ESD), of the smaller to the larger powder is less than 0.5.