# ISO 8503

Source: https://coatmentor.com/standards/iso-8503/ · Updated 2026-10-14

Surface profile (roughness) of blast-cleaned steel and how it is measured.

**Publisher**: ISO

**Area**: Surface preparation and conditions

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).

## Related

- **Concepts:** [Surface profile (anchor pattern)](https://coatmentor.com/learn/surface-profile/)
- **Standards:** [ASTM D4417](https://coatmentor.com/standards/astm-d4417/) · [ISO 19840](https://coatmentor.com/standards/iso-19840/) · [ISO 8501](https://coatmentor.com/standards/iso-8501/)

## About this page

**Also published openly:** [Elcometer 125 surface comparators](https://www.elcometer.com/en/coatings-inspection/all-coatings-inspection/surface-profile/elcometer-125-surface-comparators.html).

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](https://coatmentor.com/method/). CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.