Standard · Surface preparation and conditions
ISO 8503
Surface profile (roughness) of blast-cleaned steel and how it is measured.
ISO 8503 deals with the roughness that blast cleaning leaves on steel.
The parts an inspector meets
- Part 1: the profile comparators, one for grit (angular, "G") and one for shot (round, "S") profiles.
- Part 2: how to grade a profile with a comparator, by sight and touch, as fine, medium or coarse.
- Part 3: the focusing microscope method.
- Part 4: the stylus instrument method.
- Part 5: the replica tape method.
The grades in numbers
The grit comparator has four segments: 25, 60, 100 and 150 µm. Fine runs from the first segment up to the second, medium from the second up to the third, coarse from the third up to the fourth. A grit profile of 60 to under 100 µm is therefore medium. The shot comparator has lower segments (25, 40, 70 and 100 µm), so its grades sit lower too.
Using a comparator
- Only on Sa 2½ and Sa 3 surfaces.
- By eye, with a lens of at most ×7, or by touch with the back of a fingernail or a wooden stylus.
- For a mix of shot and grit, use the G comparator.
- Outside the range, report "finer than fine" or "coarser than coarse".
- Check a comparator in frequent use against an unused one every three months.
The grades also set the correction value that ISO 19840 subtracts from DFT readings on blasted steel: 10 µm for fine, 25 µm for medium and 40 µm for coarse.
24 practice items in the members area mention ISO 8503 (CIP 1: 11 · CIP 2: 5 · FROSIO written: 8).
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Also published openly: Elcometer 125 surface comparators.
This page describes the subject of ISO 8503 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ISO. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.