ISO 8501-1 is a visual grade at inspection time. It does not freeze the steel. Moisture plus salts start oxide at once, especially on the west coast and in monsoon.
- Bresle / salt kit before primer on marine and tank work.
- Steel a safe margin above dew point (ISO 8502-4 style check).
- Hold blasted steel under cover. Do not leave a night gap if the spec is tight.
- If flash rust is light and the spec allows, re-blast or use the holding primer the paint maker names. Do not paint over loose rust and hope.