ISO 8502-16:2026

International
Standard
ISO 8502-16
First edition
Preparation of steel substrates
2026-11
before application of paints and
related products — Tests for the
assessment of surface cleanliness —
Part 16:
Extraction of water soluble
contaminants for analysis, the
saturated filter paper method
Préparation des subjectiles d'acier avant application de peintures
et de produits assimilés — Essais pour apprécier la propreté
d'une surface —
Partie 16: Extraction des contaminants solubles dans l’eau pour
analyse, méthode du papier filtre saturé
Reference number
© ISO 2026
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Apparatus and materials . 2
5.1 Filter paper .2
5.2 Reusable syringe .2
5.3 Fresh water .2
5.4 Disposable vinyl gloves .2
5.5 Tweezers .2
5.6 Conductivity meter .2
6 Procedure . 2
6.1 Selection of test surface .2
6.2 Extraction by filter paper .2
6.3 Blank test .3
7 Analyses . 3
8 Calculation of salt density . 4
9 Test report . 4
Annex A (informative) Temperature compensation . 5
Annex B (informative) Test procedure . 6
Bibliography . 8

iii
Foreword
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bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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This document was prepared by Technical Committee ISO/TC 35, Paint and varnishes, Subcommittee SC 12,
Preparation of steel substrates before application of paints and related products.
[1]
A list of all parts in ISO 8502 (all parts) can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found atwww.iso.org/members.html.

iv
Introduction
The performance of protective coatings of paint and related products applied to steel is significantly
affected by the state of the steel surface immediately prior to painting. The principal factors that are known
to influence this performance are:
a) the presence of rust and mill scale;
b) the presence of surface contaminants, including salts, dust, oils and greases;
c) the surface profile.
[2] [1]
The series of International Standards ISO 8501 (all parts) , ISO 8502 (all parts) and ISO 8503 (all parts)
[3] [4]
have been prepared to provide methods of assessing these factors, while ISO 8504 (all parts) provides
guidance on the preparation methods that are available for cleaning steel substrates, indicating the
capabilities of each method in attaining specified levels of cleanliness. These International Standards do not
contain recommendations for the protective coating systems to be applied to the steel surface. Nor do they
contain recommendations for the surface quality requirements for specific situations, even though surface
quality can have a direct influence on the choice of protective coating to be applied and on its performance.
Such recommendations are found in other documents such as national standards and codes of practice.
Users of these International Standards are expected to ensure that the qualities specified are:
— compatible and appropriate both for the environmental conditions to which the steel will be exposed
and for the protective coating system to be used;
— within the capability of the cleaning procedure specified.
These series of International Standards referred to above deal with the following aspects of preparation of
steel substrates:
[2]
ISO 8501 (all parts) — Visual assessment of surface cleanliness;
[1]
ISO 8502 (all parts) — Tests for the assessment of surface cleanliness;
[3]
ISO 8503 (all parts) — Surface roughness characteristics of blast-cleaned steel substrates;
[4]
ISO 8504 (all parts) — Surface preparation methods.
[1]
This is one of many parts of ISO 8502 (all parts) that specify tests for the assessment of surface cleanliness.
Relating to such tests, there are several methods for extracting soluble contaminants on surfaces to be
painted, which are then used for subsequent analysis. One of these methods is based on the swabbing of
comparatively large test surfaces. This technique provides average values of the contamination present, but
it can conceal localized concentrations of contaminants. Also, it is possible that swabbing does not ensure
sufficient penetration to dissolve all the deep-seated contamination such as ferrous salts.
There are other methods which use small cells for the liquid used to remove and collect the surface
contaminants. The cells are attached to test surfaces where soluble contaminants can be expected. This
closed cell technique usually provides more accurate, point values of the contamination present than the
swabbing method.
This document describes a further, inexpensive field test using saturated filter paper to extract the soluble
salts from the surface. This method combines the benefits of testing a large area with the benefit of greater
accuracy and point measurements
...