Glossary Term
Blasting (Sa 2.5)
Blasting to Sa 2.5 describes a very thorough abrasive blast-cleaning standard for steel surface preparation before coating. The designation comes from ISO 8501-1, which uses “Sa” for blast-cleaning grades. Sa 2.5 means the surface, when viewed without magnification, is free from visible oil, grease, dirt, mill scale, rust, paint coatings, and foreign matter, with any remaining traces showing only as slight stains in the form of spots or stripes.
In yacht refit, the term appears most often in steel-hull repair, underwater-body coating renewal, tank work, and local structural repairs where the coating manufacturer or project specification calls for a high standard of cleanliness before primer application. ISO 8501-1 also makes clear that visual cleanliness is only part of the preparation picture for severe environments such as water immersion and continuous condensation; soluble salts and surface profile may also need attention through related ISO 8502 and ISO 8503 checks.
Sa 2.5 is a preparation grade, not a paint system by itself. The value of achieving it is lost quickly if dust removal is poor, contamination returns before coating, or steel temperature and dew-point separation are not controlled. That is why blasting normally sits inside a wider paint and coating repair scope with environmental control, profile checks, and timed primer application rather than as an isolated cleaning step.