In any particular environment the protection against corrosion of a zinc coating is almost directlyproportional to its thickness. When very long service life is desired, as for example on structuralsteel components, thicker coatings than those obtained by zinc electroplating are required andthese are usually applied by hot-dip galvanizing or by metal spraying.For hot-dip galvanizing see AC-STD 6769 K.The minimum thickness requirements apply only to those portions of the significantsurface that can be touched by a ball 20 mm in diameter.The significant surface is the surface of the article which, after coating, shall fulfil thestipulated requirements in respect of function or appearance.Passivation gives additional protection against corrosion and shall be applied unless there isreason to the contrary.Articles to be painted may require alternative treatment such as phosphating toprovide good adhesion.