GENERALIn any particular environment the protection against corrosion of a zinc coating isalmost directly proportional to its thickness. When very long service life is desired, asfor example on structural steel components, thicker coatings than those obtained byzinc electroplating are required and these are usually applied by hot-dip galvanizing orby 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 by chromating gives additional protection against corrosion and shall beapplied unless there is reason to the contrary.Articles to be painted may require alternative treatment such as phosphating toprovide good adhesion.