Coatings and corrosion
ISO 8501-1: Preparation of steel substrates before application of paints, visual assessment of surface cleanliness
The visual reference for how clean steel must be before painting.
Reference noteThis page is an independent plain-language summary written by QUALITAS TR. It does not reproduce the standard. Always work from the current official edition, available from ISO, the International Organization for Standardization, and national standards bodies such as TSE in Turkey (official page). QUALITAS TR supports organisations against this standard; it does not certify them.
01Purpose
ISO 8501-1 specifies rust grades and preparation grades of steel surfaces, assessed visually by comparison with representative photographs.
02Scope
Rust grades A to D describe the initial condition. Preparation grades include blast cleaning Sa 1, Sa 2, Sa 2½ and Sa 3, hand and power tool cleaning St 2 and St 3, and flame cleaning Fl.
03Main requirements
- Visual assessment with photographic references
- Preparation grade specified by the coating system
- Assessment without magnification
- Complementary standards for profile, dust and soluble salts
04Typical applications and industries
All painted steel. Sa 2½ is common for high performance systems.
05Audit and inspection considerations
- Is the grade checked before priming?
- Are dust and salts checked where specified?
- Is profile measured?
06Common nonconformities
- Mill scale remaining
- Flash rust before priming
- Dust on surface
- Profile outside specification
07How QUALITAS TR can support
Checked in every coating inspection.