What is SA 2.5 blasting in surface preparation standards?
The two dominant abrasive blasting cleaning surface preparation standards of the ISO 8501 (Sa) and the SSPC/NACE joint standards, are very difficult to compare, because they widely recognize share the same levels of cleanliness of the surface preparation grade.
The purpose of surface preparations standards exist to maximize coating/painting lifespan and minimize cleaning costs.
The ISO 8501 was published by the ISO (International Standards Organization) in 1988, combined the standard of the 1967 Swedish Standard: SIS 055900 and the German: DIN 55928. ISO 8501 is a pictorial standard showing the appearance of different rust grades at various levels of cleanliness, it also contains text descriptions of the cleanliness levels.
The China national standard GB8923-88 “Steel surface modification grade and rust removal grade before painting” divides the rust removal grade of shot blasting machine into four grades, which are represented by the letter “Sa”.
In North America, the original surface preparation standard was issued by an architectural group in the 1960s by steelworkers in Pittsburgh. The SSPC (Society for Steel Painting Structures) formed the SSPC standards are text descriptions, not pictorial, although they are accompanied by visual guides (VIS) with photo references. In 2000, SSPC and NACE issued joint standards in anticipation of a merger between the organizations and SSPC/NACE numbers them in reverse order, by increasing surface cleanliness.
ISO adapted the most common standard as Sa 2 1/2, Very Thorough Blasting Cleaning, while SSPC used as SP 10 Near White. The two versions were not equal: Sa 2.5 permitted stains, streaks and shadows from rust, mill scale and coatings to remain on up to 15% of the surface, whereas SP 10 allowed for only 5%.