One of the things that I did during my inspection career was check for paint film thickness. To put it simply you really want enough!
The chances of you getting it with a rattle can are slim, and you ask why. The aerosol can is simply a tank filled with compressed air or gas that pushes out the paint when you press the valve. In a 12 ounce aerosol can there is about 4 ounces of paint product, 2 or 3 ounces of solvent and the rest is the propellant. You are according to one source at best going to get a .05mil paint film and you want as a minimum 1.5mil or more.
One alternative for frames is to use zinc rich, cold galvanizing spray "Cold galvanizing coating. Zinc-rich Galvax stops rust and corrosion caused by welding and atmospheric exposure. High percentage of pure zinc dust in an epoxy resin formulation produces a film providing years of protection. Electro-chemically bonds with iron and steel, and actually fuses with the base metal to provide rust and corrosion resistance. Equal to hot dip galvanizing in cathodic protection, film durability, and protection against caustic action of salt. Can be used as a primer for most paints. Galvax sprays or brushes on cold and heals itself when scratched. Excellent for recoating or spot-priming weathered galvanized surfaces and repairing areas damaged by welding."
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