Single and Twin Pack Etch Primers

The priming of non-ferrous metals became an issue during World War 2 when aircraft and ships were starting to be built using aluminium rather than the heavier steel previously used. The U.S. military claim the original development of etch primers and their introduction into the coating industry. Phosphoric acid, when added to paints based on phenolic/polyvinyl butyral resins provide the adhesion required to successfully coat 'difficult' metals. Anti-corrosive pigments such as zinc tetroxy chromate were used to provide the protection against corrosion.
After the withdrawal of calcium plumbate, and chromate pigments from the market due to health risks attached to their use, etch primers have been more and more popular, not only for priming non-ferrous metals, but as the first choice in primer for ferrous and galvanised metals as well. The solvent blend used is rich in alcohols, making the coating quick drying. The product can be applied by spray  as well as by brush or roller.
As a rule, in the South African coating market, single pack etch primers are applied to galvanised iron or ferrous metals, and twin pack etch primers are applied to non-ferrous metals (mostly aluminium or stainless steel), usually by spray application. Twin pack etch primers have, in addition to this, been very successfully used to prime glass-fibre substrates for subsequent coating.