ISO 8501-1 Preparation of steel substrates before application of paints – Visual assessment of surface cleanliness

Defines rust grades of unpainted steel and preparation grades such as Sa 2½ for blast cleaning, illustrated with reference photographs.

CodeISO 8501-1Issued byISOFieldSurface preparation

What it covers

Rust grades A–D of the initial surface.
Preparation grades for blast cleaning (Sa 1, Sa 2, Sa 2½, Sa 3), hand and power tool cleaning (St 2, St 3) and flame cleaning.

Sa 2½ is the usual grade for structural paint systems.
Cleanliness is assessed visually against the reference photographs, together with surface profile and dust checks.

Blasting can be a stage with a QC step “Sa 2½” from the QC library, so painting cannot start before the surface is accepted.

This page is a summary for orientation. Always work from the edition of the standard named in the project specification.

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Mis à jour le 01 Nov 2026

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