# ASTM D4940

Source: https://coatmentor.com/standards/astm-d4940/ · Updated 2026-10-14

Soluble salt contamination of blast abrasives, by conductivity.

**Publisher**: ASTM International

**Area**: Surface preparation and conditions

ASTM D4940 checks blast abrasive for soluble salts before they reach the steel. It measures the electrical conductivity of water that has soaked the abrasive.

## The procedure

Mix equal volumes of abrasive and deionized water, 300 mL each. Stir for a minute, let it stand for 8 minutes, stir again, filter and measure the conductivity of the filtrate.

## Points to remember

- Conductivity shows all the dissolved salts together. It does not say which ions they are, so it is not a chloride test.
- D4940 is a test method only. The limit comes from the abrasive standard: the SSPC abrasive standards allow at most 1,000 µS/cm. A meter that shows mS/m reads that limit as 100 mS/m.

## Not the ISO method

ISO 11127-6 also uses conductivity, but with a different ratio and a longer soak, and ISO 11126 sets its own, lower limit for new slags. A result by one method cannot be judged against the limit of the other, so the specification names the method together with the limit.

**1** practice item in the members area mentions ASTM D4940 (CIP 2: 1).

## Related

- **Concepts:** [Soluble salts and the Bresle test](https://coatmentor.com/learn/soluble-salts/)
- **Standards:** [SSPC-AB 1, AB 2 and AB 3](https://coatmentor.com/standards/sspc-ab-1-2-3/) · [ASTM D7393](https://coatmentor.com/standards/astm-d7393/) · [ISO 11124 to 11127](https://coatmentor.com/standards/iso-11124-11127/)

## About this page

**Also published openly:** [KTA-Tator: abrasive conductivity testing to ASTM D4940](https://kta.com/abrasive-testing-in-the-shop-field/).

This page describes the subject of ASTM D4940 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ASTM International. 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.