EN ISO 12944-4:2017

SLOVENSKI STANDARD
01-februar-2018
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SIST EN ISO 12944-4:1998
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Paints and varnishes - Corrosion protection of steel structures by protective paint
systems - Part 4: Types of surface and surface preparation (ISO 12944-4:2017)
Beschichtungsstoffe - Korrosionsschutz von Stahlbauten durch Beschichtungssysteme -
Teil 4: Arten von Oberflächen und Oberflächenvorbereitung (ISO 12944-4:2017)
Peintures et vernis - Anticorrosion des structures en acier par systèmes de peinture -
Partie 4: Types de surface et de préparation de surface (ISO 12944-4:2017)
Ta slovenski standard je istoveten z: EN ISO 12944-4:2017
ICS:
25.220.10 Priprava površine Surface preparation
87.040 Barve in laki Paints and varnishes
91.080.13 Jeklene konstrukcije Steel structures
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 12944-4
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2017
EUROPÄISCHE NORM
ICS 25.220.10; 87.020; 91.080.13 Supersedes EN ISO 12944-4:1998
English Version
Paints and varnishes - Corrosion protection of steel
structures by protective paint systems - Part 4: Types of
surface and surface preparation (ISO 12944-4:2017)
Peintures et vernis - Anticorrosion des structures en Beschichtungsstoffe - Korrosionsschutz von
acier par systèmes de peinture - Partie 4: Types de Stahlbauten durch Beschichtungssysteme - Teil 4:
surface et de préparation de surface (ISO 12944- Arten von Oberflächen und Oberflächenvorbereitung
4:2017) (ISO 12944-4:2017)
This European Standard was approved by CEN on 30 October 2017.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 12944-4:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
European foreword
This document (EN ISO 12944-4:2017) has been prepared by Technical Committee ISO/TC 35 “Paints
and varnishes” in collaboration with Technical Committee CEN/TC 139 “Paints and varnishes” the
secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2018, and conflicting national standards shall be
withdrawn at the latest by June 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 12944-4:1998.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 12944-4:2017 has been approved by CEN as EN ISO 12944-4:2017 without any
modification.
INTERNATIONAL ISO
STANDARD 12944-4
Second edition
2017-11
Paints and varnishes — Corrosion
protection of steel structures by
protective paint systems —
Part 4:
Types of surface and surface
preparation
Peintures et vernis — Anticorrosion des structures en acier par
systèmes de peinture —
Partie 4: Types de surface et de préparation de surface
Reference number
ISO 12944-4:2017(E)
©
ISO 2017
ISO 12944-4:2017(E)
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

ISO 12944-4:2017(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 General . 4
5 Types of surface to be prepared . 4
5.1 General . 4
5.2 Uncoated surfaces . 4
5.3 Metal-coated surfaces . 4
5.3.1 Thermally sprayed surfaces . 4
5.3.2 Hot-dip-galvanized surfaces . 4
5.3.3 Zinc-electroplated surfaces . 4
5.3.4 Sherardized surfaces . 5
5.4 Surfaces painted with prefabrication primer . 5
5.5 Other painted surfaces . 5
5.6 Surfaces with chemical treatment . 5
6 Surface preparation methods . 5
6.1 General . 5
6.2 Water, solvent and chemical cleaning. 5
6.2.1 Water cleaning . 5
6.2.2 Steam cleaning . 5
6.2.3 Emulsion cleaning . . . 6
6.2.4 Alkaline cleaning . 6
6.2.5 Organic-solvent cleaning . 6
6.2.6 Stripping. 6
6.2.7 Acid pickling . 6
6.2.8 Chemical treatment . 6
6.3 Mechanical cleaning . 6
6.3.1 Hand-tool cleaning . 6
6.3.2 Power-tool cleaning . 6
6.3.3 Blast-cleaning . 7
6.3.4 Water jetting . 8
7 Surface preparation grades . 8
7.1 General . 8
7.2 Uncoated surfaces . 9
7.3 Metal-coated surfaces . 9
7.4 Surfaces painted with prefabrication primer . 9
7.5 Other painted surfaces . 9
8 Surface profile (roughness) and surface profile grading .10
9 Assessment of prepared surfaces .10
10 Temporary protection of prepared surfaces from corrosion and/or contamination .10
11 Preparation of temporarily or partly protected surfaces before application of
further coatings .10
12 Preparation of hot-dip-galvanized surfaces .11
12.1 Unweathered surfaces .11
12.2 Weathered surfaces .11
13 Preparation of thermally sprayed metal (zinc and aluminium) surfaces .11
ISO 12944-4:2017(E)
14 Preparation of zinc-electroplated and sherardized surfaces .11
15 Preparation of other coated surfaces .12
16 Recommendations regarding pollution and the environment .12
17 Health and safety .12
Annex A (normative) Standard preparation grades for primary (overall) surface preparation .13
Annex B (normative) Standard preparation grades for secondary (partial) surface preparation .15
Annex C (informative) Procedures for removal of extraneous layers and foreign matter,
native layers and contaminants .17
Bibliography .19
iv © ISO 2017 – All rights reserved

ISO 12944-4:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee
SC 14, Protective paint systems for steel structures.
This second edition cancels and replaces the first edition (ISO 12944-4:1998), which has been
technically revised.
The main changes compared to the previous edition are as follows:
— the terms and definitions which were not used in the main part of the standard have been deleted;
— the normative references have been updated;
— 5.6 “Surfaces with chemical treatment” has been included;
— 6.2.8 “Chemical treatment” has been included;
— Annex C has been restructured to contain two tables for distinction between “extraneous layers
and foreign matter” and “native layers and contaminants”;
— the bibliography has been updated;
— the text has been editorially revised.
A list of all parts in the ISO 12944 series can be found on the ISO website.
ISO 12944-4:2017(E)
Introduction
Unprotected steel in the atmosphere, in water and in soil is subjected to corrosion that can lead to
damage. Therefore, to avoid corrosion damage, steel structures are normally protected to withstand
the corrosion stresses to which they will be subjected during the service life required of the structure.
There are different ways of protecting steel structures from corrosion. ISO 12944 (all parts) deals with
protection by paint systems and covers, in the various parts, all features that are important in achieving
adequate corrosion protection. Additional or other measures are possible but require particular
agreement between the interested parties.
In order to ensure effective corrosion protection of steel structures, owners of such structures, planners,
consultants, companies carrying out corrosion protection work, inspectors of protective coatings
and manufacturers of coating materials need to have at their disposal state-of-the-art information in
concise form on corrosion protection by paint systems. It is vital that such information is as complete as
possible, unambiguous and easily understandable to avoid difficulties and misunderstandings between
the parties concerned with the practical implementation of protection work.
ISO 12944 (all parts) is intended to give this information in the form of a series of instructions. It is
written for those who have some technical knowledge. It is also assumed that the user of ISO 12944 (all
parts) is familiar with other relevant International Standards, in particular those dealing with surface
preparation.
Although ISO 12944 (all parts) does not deal with financial and contractual questions, attention is
drawn to the fact that, because of the considerable implications of inadequate corrosion protection,
non-compliance with requirements and recommendations given in ISO 12944 (all parts) can result in
serious financial consequences.
ISO 12944-1 defines the overall scope of ISO 12944. It gives some basic terms and definitions and a
general introduction to the other parts of ISO 12944. Furthermore, it includes a general statement on
health, safety and environmental protection, and guidelines for using ISO 12944 (all parts) for a given
project.
This document describes the different types of surface to be protected and gives information on surface
preparation methods such as chemical and mechanical cleaning. It deals with surface preparation
grades, surface profile (roughness), assessment of prepared surfaces, temporary protection of
prepared surfaces, preparation of temporarily protected surfaces for further coatings, preparation of
existing metal coatings, and environmental aspects. As far as possible, reference is made to the basic
International Standards on the surface preparation of steel substrates before application of paints and
related products.
vi © ISO 2017 – All rights reserved

INTERNATIONAL STANDARD ISO 12944-4:2017(E)
Paints and varnishes — Corrosion protection of steel
structures by protective paint systems —
Part 4:
Types of surface and surface preparation
1 Scope
This document covers the following types of surfaces of steel structures consisting of carbon or low-
alloy steel, and their preparation:
— uncoated surfaces;
— surfaces thermally sprayed with zinc, aluminium or their alloys;
— hot-dip-galvanized surfaces;
— zinc-electroplated surfaces;
— sherardized surfaces;
— surfaces painted with prefabrication primer;
— other painted surfaces.
This document defines a number of surface preparation grades but does not specify any requirements
for the condition of the substrate prior to surface preparation.
Highly polished surfaces and work-hardened surfaces are not covered by this document.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 1461, Hot dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods
ISO 2063 (all parts), Thermal spraying — Zinc, aluminium and their alloys
ISO 4628-1, Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity
and size of defects, and of intensity of uniform changes in appearance — Part 1: General introduction and
designation system
ISO 4628-2, Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity
and size of defects, and of intensity of uniform changes in appearance — Part 2: Assessment of degree of
blistering
ISO 4628-3, Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity and
size of defects, and of intensity of uniform changes in appearance — Part 3: Assessment of degree of rusting
ISO 4628-4, Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity
and size of defects, and of intensity of uniform changes in appearance — Part 4: Assessment of degree of
cracking
ISO 12944-4:2017(E)
ISO 4628-5, Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity and
size of defects, and of intensity of uniform changes in appearance — Part 5: Assessment of degree of flaking
ISO 4628-6, Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity
and size of defects, and of intensity of uniform changes in appearance — Part 6: Assessment of degree of
chalking by tape method
ISO 8501-1:2007, Preparation of steel substrates before application of paints and related products —
Visual assessment of surface cleanliness — Part 1: Rust grades and preparation grades of uncoated steel
substrates and of steel substrates after overall removal of previous coatings
ISO 8501-2:1994, Preparation of steel substrates before application of paints and related products — Visual
assessment of surface cleanliness — Part 2: Preparation grades of previously coated steel substrates after
localized removal of previous coatings
ISO 8501-3, Preparation of steel substrates before application of paints and related products — Visual
assessment of surface cleanliness — Part 3: Preparation grades of welds, edges and other areas with surface
imperfections
ISO 8501-4, Preparation of steel substrates before application of paints and related products — Visual
assessment of surface cleanliness — Part 4: Initial surface conditions, preparation grades and flash rust
grades in connection with high-pressure water jetting
ISO 8504 (all parts), Preparation of steel substrates before application of paints and related products —
Surface preparation methods
ISO 12944-1, Paints and varnishes — Corrosion protection of steel structures by protective paint systems —
Part 1: General introduction
ISO 16276 (all parts), Corrosion protection of steel structures by protective paint systems — Assessment of,
and acceptance criteria for, the adhesion/cohesion (fracture strength) of a coating
EN 10238, Automatically blast-cleaned and automatically prefabrication primed structural steel products
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12944-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
abrasive blast-cleaning
impingement of a high-kinetic-energy stream of blast-cleaning abrasive (3.2) on to the surface to be
prepared
[SOURCE: ISO 11124-1:1993, 2.2]
3.2
blast-cleaning abrasive
solid material intended to be used for abrasive blast-cleaning (3.1)
[SOURCE: ISO 11124-1:1993, 2.1]
2 © ISO 2017 – All rights reserved

ISO 12944-4:2017(E)
3.3
dust
loose particulate matter present on a steel surface prepared for painting, arising from blast-cleaning
(3.1) or other surface preparation processes, or resulting from the action of the environment
[SOURCE: ISO 8502-3:2017, 3.1]
3.4
dew point
temperature at which moisture in the air will condense out on to a solid surface
Note 1 to entry: See ISO 8502-4.
3.5
flash rusting
slight rust formation on a prepared steel surface soon after preparation
3.6
grit
particles that are predominantly angular, that have fractured faces and sharp edges and that are less
than half-round in shape
[SOURCE: ISO 11124-1:1993, 2.4]
3.7
mill scale
heavy oxide layer formed during hot fabrication or heat treatment of steel
3.8
rust
visible corrosion products consisting, in the case of ferrous metals, mainly of hydrated iron oxides
3.9
shot
particles that are predominantly round, that have a length of less than twice the maximum particle
width and that do not have edges, broken faces or other sharp surface defects
[SOURCE: ISO 11124-1:1993, 2.3]
3.10
substrate
surface to which a coating material is applied or is to be applied
[SOURCE: ISO 4618:2014, 2.244]
3.11
surface preparation
method of preparing a surface for coating
3.12
white rust
white to dark grey corrosion products on zinc-coated surfaces
3.13
chemical treatment
surface treatment process, based on a chemical or electrochemical reaction, which superficially
modifies the metal substrate (3.10)
ISO 12944-4:2017(E)
4 General
The primary objective of surface preparation is to ensure the removal of matter which negatively affects
the corrosion protection and to obtain a surface that permits satisfactory adhesion of the coating to the
surface. It will also assist in reducing the amounts of contaminants that initiate corrosion.
It is stressed that there is a very wide variation in the condition of steel surfaces requiring cleaning
prior to painting. This particularly applies to maintenance of an already coated structure. The age
of the structure and its location, the quality of the previous surface, the performance of the existing
coating system and the extent of breakdown, the type and severity of previous and future corrosion
environments, and the intended new coating system, all influence the amount of preparation required.
When selecting a surface preparation method, it is necessary to consider the preparation grade
(according to this document) required to give a level of surface cleanliness and, if required, a surface
profile (roughness) appropriate to the coating system to be applied to the steel surface.
Personnel carrying out surface preparation work shall have suitable equipment and sufficient
technical knowledge of the processes involved to enable them to carry out the work in accordance with
the required specification. It is important that the surfaces to be treated are readily accessible and
sufficiently illuminated. All surface preparation work shall be properly supervised and inspected.
If the specified preparation grade has not been achieved by the preparation method selected or when
the condition of the prepared surface has subsequently changed before the application of the coating
system, relevant parts of the procedure shall be repeated so as to obtain the specified preparation grade.
Details regarding the preliminary treatment of welds, the removal of weld spatter and removal of burrs
and other sharp edges shall be in accordance with ISO 8501-3. Details are given in ISO 12944-3. These
measures should normally be taken in connection with the manufacturing process before the surface
preparation.
NOTE For further details, see ISO 8504-1.
5 Types of surface to be prepared
5.1 General
The different types of surface shall be prepared as described in 5.2 to 5.6.
5.2 Uncoated surfaces
Uncoated surfaces consist of bare steel, which can be covered by mill scale or rust and other
contaminants. They shall be assessed in accordance with ISO 8501-1 (rust grades A, B, C and D).
5.3 Metal-coated surfaces
5.3.1 Thermally sprayed surfaces
Thermally sprayed surfaces consist of steel coated with zinc, aluminium or their alloys by flame or arc
spraying in accordance with ISO 2063 (all parts).
5.3.2 Hot-dip-galvanized surfaces
Hot-dip-galvanized surfaces consist of steel coated with zinc or zinc alloy by immersion in a molten
bath in accordance with ISO 1461.
5.3.3 Zinc-electroplated surfaces
Zinc-electroplated surfaces consist of steel coated with an electrodeposited zinc coating.
4 © ISO 2017 – All rights reserved

ISO 12944-4:2017(E)
5.3.4 Sherardized surfaces
Sherardized surfaces consist of steel coated with zinc-iron alloy layers obtained by heating the steel
component in a container together with zinc dust.
5.4 Surfaces painted with prefabrication primer
Surfaces painted with prefabrication primer consist of automatically blast-cleaned steel to which a
prefabrication primer has been applied automatically in a plant, in accordance with EN 10238.
NOTE For the purpose of this document, the expression “surfaces painted with prefabrication primer” has a
restricted meaning, as defined in EN 10238. It is restricted to automatic blast-cleaning and automatic priming.
5.5 Other painted surfaces
Other painted surfaces consist of steel/metal-coated steel that has already been painted (see 7.5).
5.6 Surfaces with chemical treatment
In some specific uses, chemical treatments are implemented to enhance corrosion resistance and/or to
improve paint bonding, before metal painting operations.
With regard to this document, chemical treatment refers to hot-dip-galvanized steel surfaces,
electroplated-zinc steel surfaces and sherardized surfaces.
Chemical treatment includes a dedicated cleaning followed by the chemical treatment itself conducted
by spray, runoff or immersion, usually ending with a final step of rinsing.
The paint manufacturer shall previously confirm compatibility of the paint system with the chemical
pre-treatment.
6 Surface preparation methods
6.1 General
The use of the methods described in 6.2 and 6.3 requires surface preparation, in accordance with
ISO 8504 (all parts). Oil, grease, salts, dirt and similar contaminants shall be removed after agreement
between the involved parties, prior to further surface preparation, using an appropriate method. In
addition, prior removal of heavy, firmly adhering rust and mill scale by suitable manual or mechanical
techniques can be necessary. Where metal-coated steel is to be cleaned, the technique shall not
unnecessarily remove sound metal. A survey of cleaning methods is given in Annex C. The different
methods listed are not exhaustive.
6.2 Water, solvent and chemical cleaning
6.2.1 Water cleaning
This method consists of directing a jet of clean, fresh water on to the surface to be cleaned. The water
pressure required depends on the contaminants to be removed such as water-soluble materials, loose
rust and poorly adhering paint coatings. To remove oil, grease, etc., the addition of suitable detergents
is necessary. When detergents have been used in the cleaning operation, rinsing with clean, fresh water
is necessary.
6.2.2 Steam cleaning
Steam cleaning is carried out to remove oil, grease, salts, dirt and similar contaminants. If a detergent is
added to the steam, rinsing with clean, fresh water is necessary.
ISO 12944-4:2017(E)
6.2.3 Emulsion cleaning
Emulsion cleaning is carried out to remove oil, grease, salts, dirt and similar contaminants using
emulsion cleaners, followed by rinsing with clean, fresh (hot or cold) water.
6.2.4 Alkaline cleaning
Alkaline cleaning is carried out to remove oil, grease, salts, dirt and similar contaminants by using
alkaline cleaners, followed by rinsing using clean, fresh (hot or cold) water.
6.2.5 Organic-solvent cleaning
Organic-solvent cleaning is carried out to remove grease or oil by using suitable organic solvents.
Degreasing with rags impregnated with organic solvent is usually restricted to small areas.
6.2.6 Stripping
Stripping is the removal of paint coatings by solvent-borne pastes (for coatings soluble in solvents)
or alkaline pastes (for saponifiable coatings). It is normally restricted to small areas. Appropriate
subsequent cleaning is necessary.
6.2.7 Acid pickling
Acid pickling (Be) involves immersion of the component in a bath containing a suitable inhibited acid
which removes mill scale and rust. The exposed surface shall not be appreciably attacked.
Acid pickling is only suitable for use under carefully monitored factory conditions and is not normally
a site process.
6.2.8 Chemical treatment
The quality of the surface treatment shall be assessed in accordance with the specifications of the
surface treatment supplier before being processed to the paint application.
After complete chemical pre-treatment, the surface provided is deemed ready to use for painting. The
work piece surfaces shall be completely dry and clean. If relevant, specific attention shall be paid to the
maximum recovery time allowed to start the painting process, according to the recommendations of
the surface treatment supplier.
6.3 Mechanical cleaning
6.3.1 Hand-tool cleaning
Typical hand tools include wire brushes, spatulas, scrapers, synthetic-fabric pads with embedded
abrasives, emery cloth and rust-chipping hammers. For further details, see ISO 8504-3.
6.3.2 Power-tool cleaning
Typical power tools include rotating wire brushes, various types of grinder, percussion hammers and
needle guns. Surface areas that cannot be reached with such tools shall be prepared by hand. The
cleaning operation shall not cause any damage or deformation of the structural elements and care shall
be taken to avoid the type of surface damage that chipping tools are liable to cause (notching). When
wire brushes are used, it shall be ensured that rust and contaminants are not merely polished. Polished
rust and mill scale can develop a sheen that looks like clean metal, but which would impair the adhesion
of any coating applied to it. Cleaning with power tools is more effective in terms of area covered and
degree of cleanliness than manual surface preparation, but is not nearly as effective as blast-cleaning.
This should be borne in mind in those cases where power-tool cleaning is preferred to blast-cleaning
6 © ISO 2017 – All rights reserved

ISO 12944-4:2017(E)
(e.g. where the generation of dust or the accumulation of used abrasive is to be avoided). For further
details, see ISO 8504-3.
6.3.3 Blast-cleaning
One of the methods specified in ISO 8504-2 shall be used. Blast-cleaning abrasives shall be specified by
reference to the various parts of ISO 11124 and ISO 11126.
6.3.3.1 Dry abrasive blast-cleaning
6.3.3.1.1 Centrifugal abrasive blast-cleaning
Centrifugal abrasive blast-cleaning is carried out in fixed installations or mobile units in which the
abrasive is fed to rotating wheels or impellers positioned to throw the abrasive evenly and at high
velocity on to the surfaces to be cleaned.
For the fields of application, effectiveness and limitations of this technique, see ISO 8504-2.
6.3.3.1.2 Compressed-air abrasive blast-cleaning
Compressed-air abrasive blast-cleaning is carried out by feeding the abrasive into an air stream and
directing the air/abrasive mixture at high velocity from the nozzle on to the surface to be cleaned.
The abrasive can be injected into the air stream from a pressurized container or can be drawn into the
air stream by suction from an unpressurized container.
For the field of application, effectiveness and limitations of this technique, see ISO 8504-2.
6.3.3.1.3 Vacuum or suction-head abrasive blast-cleaning
This method is similar to compressed-air abrasive blast-cleaning (see 6.3.3.1.2) but with the blast nozzle
enclosed in a suction head sealed to the steel surface, collecting the spent abrasive and contaminants.
Alternatively, the air/abrasive stream can be sucked on to the surface by reduced pressure at the
suction head.
For the field of application, effectiveness and limitations of this technique, see ISO 8504-2.
6.3.3.2 Moisture-injection abrasive blast-cleaning (compressed-air moisture-injection abrasive
blast-cleaning)
This method is similar to compressed-air abrasive blast-cleaning (see 6.3.3.1.2) but with the addition
of a very small amount of liquid (usually clean, fresh water), upstream of the nozzle, to the air/abrasive
stream, resulting in a blast-cleaning procedure which is dust-free in the suspended-particle size range
of less than 50 µm. The consumption of water can be controlled and is usually 15 l/h to 25 l/h.
For the field of application, effectiveness and limitations of this technique, see ISO 8504-2.
6.3.3.3 Wet abrasive blast-cleaning
6.3.3.3.1 Compressed-air wet abrasive blast-cleaning
This method is similar to compressed-air abrasive blast-cleaning (see 6.3.3.1.2) but with the addition of
liquid (generally clean, fresh water) to produce a stream of air, water and abrasive.
For the field of application, effectiveness and limitations of this technique, see ISO 8504-2.
ISO 12944-4:2017(E)
6.3.3.3.2 Slurry blast-cleaning
A dispersion of fine abrasive in water or another liquid is directed, with pumps or compressed air, on to
the surface to be cleaned.
For the field of application, effectiveness and limitations of this technique, see ISO 8504-2.
6.3.3.3.3 Pressurized-liquid blast-cleaning
An abrasive (or a mixture of abrasives) is introduced into a stream of liquid (generally clean, fresh
water) and the stream directed through a nozzle on to the surface.
The stream is predominantly pressurized liquid, and additions of solid abrasives are normally less than
for compressed-air wet abrasive blast-cleaning.
The abrasive can be introduced either as dry (with or without air) or as wet slurry.
For the field of application, effectiveness and limitations of this technique, see ISO 8504-2.
6.3.3.4 Particular applications of blast-cleaning
6.3.3.4.1 Sweep blast-cleaning
The aim of sweep blast-cleaning is to clean or roughen organic and metallic coatings on the surface only,
or to remove a surface layer (or a poorly adhering coating) in such a way that a firmly adhering coating
under it is neither pitted by particle impact nor stripped down to the substrate. The required surface
condition shall be agreed between the interested parties. For this purpose, a test area can be prepared
and assessed, and the various blast-cleaning parameters, e.g. hardness of abrasive, attack angle,
distance from nozzle to substrate, air pressure and particle size of abrasive, can be optimized. Normally
for sweep blast-cleaning, low air pressure and fine-grained, grit blast-cleaning abrasive is used.
6.3.3.4.2 Spot blast-cleaning
Spot blast-cleaning is a common form of compressed-air or moisture-injection blast-cleaning in which
only individual stains (e.g. rust or weld spots) in an otherwise intact coating are blast-cleaned. It can
be carried out in conjunction with sweep blast-cleaning of the other surfaces where these cannot be
recoated without prior cleaning. Depending on the intensity of the blast-cleaning, the result will then
be equivalent to preparation grade P Sa 2 or P Sa 2 1/2.
6.3.4 Water jetting
This method consists in directing a jet of pressurized clean, fresh water on to the surface to be cleaned.
The water pressure depends on the contaminants to be removed, such as water-soluble matter, loose
rust and poorly adhering paint coatings. When detergents have been used in the cleaning operation,
rinsing with clean, fresh water is necessary. High-pressure water jetting and ultra-high-pressure water
jetting shall be in accordance with ISO 8501-4.
7 Surface preparation grades
7.1 General
Requirements shall be based on the preparation grades listed in Annexes A and B.
Other preparation grades can be agreed on the basis of representative photographic examples or
reference areas on the surface of th
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