It is important to eliminate all traces of mill scale and corrosion prior to the application of paints. Here are several methods to clean the surface of rust and scale.
CHIPPING: Chipping and wire brushing, (not suitable for preparation of substrates to be coated with high performance paint systems such as 2 Pack Epoxy High Build Coatings.)
FLAME CLEANING: Flame Cleaning can be used to remove scale however not rust.
WIRE BRUSHING: Wire brushing, usually carried out with rotating or hand wire brushes. Not suitable for the removal of mill scale. The wire brushed surfaces aren’t completely free of corrosion. They can be polished and contaminated with oil, which decreases the adhesion of the primer coat. Disc sanding is usually required to complete the preparation.
SWEEP OR LIGHT BLAST CLEANING: Sweep / light blast cleaning to remove any light rust and surface contamination from a painted steel surface.
BLAST CLEANING: Blast cleaning involves forcing a stream of abrasive particles at speed against the surface to be prepared. It can either be hand operated or automatic. This is the best method of preparation. Commonly two types are used, “Shot” where the particles are mostly spherical and should contain only a minimum of irregular shapes. And “Grit”, where the particles show angularity of form and have shape cutting edges.
After steel is prepared a suitable paint system should be applied. The primer coat needs to be applied as soon as possible to prevent further corrosion of the metal surface.