Preparation Definitions for Specifications
Sa 3 The surface of the steel is metallic-white, there are no traces of corrosion or shadow after blast cleaning.
Sa 2 1/2 Careful abrasive blast cleaning. The surface is metallic-white, there are no traces of corrosion but some lightly coloured greyish shadows might remain.
Sa 2 This preparation should lead to the almost entire elimination of traces of rust and scale. Some points of corrosion might remain and some very adherent mill scale particles after blast cleaning.
Sa 1 Sweep blasting. Some oxidised parts and scale remain. The metal maintains the colour of rust.
St 3 Operation usually applied to pre-primed steel or de-scaled raw steel. Brushing, abrasive discs and mechanical grinding are employed. The surface must have a very clean metallic-white appearance.
St 2 Operation conducted manually by brushing with a steel brush, scraping etc. The aim is to eliminate powdery, non-adherent and scaly corrosion. The appearance is a light metallic gloss.
After blast cleaning iron or steel, the surface will have a rough profile which will affect the coverage of paint. The surface area is thus larger, hence will require more paint.