Abrasive blasting is the method generally used to prepare metals for coating, by propelling an abrasive medium forcibly against the metal surface. In shot blasting, the medium used is smooth steel shot.

The better the method used, the better the preparedness of the metal surface and therefore the effectiveness of the applied coating. There are three commonly used systems of standards denoting the condition of the metal surface; SSPC (managed by the USA Coating Society), NACE (managed by the British National Association of Corrosion Engineers), and Swedish Standards.

Since 1967, the Swedish system of classification (SIS 055900) has gained international recognition as a comprehensive set of standards for surface preparation, and has been adopted in its entirety in many countries.

There are four basic levels of surface cleanliness described by the Swedish system, ranging between SA1 (essentially the removal of loose material such as dirt, rust and scale) and SA3, the highest level.

For SA3, described as ‘White Metal’, visible mill scale, dirt, grease, rust and foreign particles are completely removed and the cleaned surface has a uniform metallic colour.

This highest standard of surface preparation is crucial to the success of any subsequent application of a corrosion protection system. SA3 ensures that the surface is not only clean, but also profiled so as to maximise the adhesion of coatings.