Class 1: steel recommended for hot-dip galvanization when aesthetic appearance is important: highly visible architectural applications and structures, such as lighting columns and urban furniture. This steel is also the most suitable material for structures which require long periods of immersion in zinc.
Class 2: coatings in non-extended immersions for an average look. These can exhibit frequent outbreaks of reactive coating (spotted, grooved or tree bark effects). They provide local coatings of up to 500 microns of thickness.
Class 3: These provide thick and rough coatings with little or no eta layer (pure zinc). Poor adhesion appears in prolonged immersion times. Frequent surface defects, poor aspect and common damages. With phosphorus levels above 0.4%, it is not possible to reach acceptable coatings in normal immersion times.
Classes 4a, 4b and 5a: Suitable for highly-resistant coatings (coating thickness above 105 microns). They can be very fragile and flake in immersions over ten minutes.
Classes 5b and 6: hey are not recommended for general galvanization, except for immersion periods of less than two or three minutes.