When viewed without magnification, the surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter of at least 66-2/3% of unit area, which shall be a square 3 in. x 3 in. (9 sq. in.). Light shadows, slight streaks, or minor discolorations caused by stains of rust, stains of mill scale, or stains of previously applied coating in less than 33-1/3% of the unit area is acceptable.
This is the most commonly specified grade of abrasive blasting and is suitable for most industrial coatings when not intended for immersion service. Prior to blast cleaning, visible deposits of oil and/or grease should be removed by power washing or other agreed upon methods. In addition, sharp fins, edges and weld spatter should be removed. The profile produced by blasting should be controlled by the selection of blast media and should not exceed the filling capacity of the primer to be applied.
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