ISO/TS 16688:2017

TECHNICAL ISO/TS
SPECIFICATION 16688
First edition
2017-11
Guidelines for the selection of coating
types, tests and methods of assessing
the performance of coated aluminium
in architectural applications
Lignes directrices pour la sélection des types de revêtements, essais et
méthodes d’évaluation des performances de l’aluminium revêtu dans
les applications architecturales
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
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ii © ISO 2017 – All rights reserved

Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 3
4.1 Selection of methods to protect metals against corrosion . 3
4.2 System for selecting coating types for architectural applications . 3
5 Types of environment . 4
6 Classification of coatings . 7
6.1 Specifications for coated aluminium products . 7
6.2 Descriptions of coatings and coating processes . 8
6.3 Classifications of anodic oxidation coatings . 8
6.4 Classifications of paint coatings . 9
6.5 Classifications of combined coatings .10
6.6 Comparison of the classifications .10
7 Coating selection for different environments .10
8 Durability tests .12
8.1 General .12
8.2 Mechanical durability .12
8.2.1 General.12
8.2.2 Deformation .12
8.2.3 Indentation (hardness) .14
8.2.4 Abrasive and adhesive wear .15
8.2.5 Erosion.15
8.3 Chemical durability .16
8.3.1 General.16
8.3.2 Immersion tests .16
8.3.3 Spot and ring tests .19
8.3.4 Poultice or pat tests .20
8.3.5 Tests using an absorbent medium .20
8.3.6 Spray tests .20
8.3.7 Tests involving exposure to vapours or gases .21
8.4 Radiation and heat resistance .21
8.5 Weathering resistance .23
8.5.1 Resistance to artificial weathering .23
8.5.2 Resistance to natural weathering .23
9 Selection of test methods to enable the comparison of different coating types for
service in different environments .23
10 Methods of measuring performance .25
10.1 General .25
10.2 Appearance .26
10.2.1 Visible defects . .26
10.2.2 Colour .26
10.2.3 Reflectance .27
10.3 Coating integrity .28
10.3.1 Loss of adhesion or cohesion .28
10.3.2 Loss of coating thickness .28
10.3.3 Loss of coating mass or density .29
10.3.4 Change of electrical resistance .29
10.3.5 Increase in absorptivity .30
Annex A (informative) Recommended cleaning procedures for coated aluminium
architectural materials .31
Bibliography .32
iv © ISO 2017 – All rights reserved

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 79, Light metals and their alloys,
Subcommittee SC 2, Organic and anodic oxidation coatings on aluminium.
TECHNICAL SPECIFICATION ISO/TS 16688:2017(E)
Guidelines for the selection of coating types, tests
and methods of assessing the performance of coated
aluminium in architectural applications
1 Scope
This document establishes a system to select coating types for architectural applications depending
on environment. It gives guidelines for the selection of tests and methods of measuring performance in
terms that are of direct interest to the building designer.
This document is applicable to organic and anodic oxidation (AAO) coatings on aluminium, including
those produced from liquid and powder paints, and combined coatings of organic and anodic oxidation
coatings. It is designed to be applicable to novel coatings developed in the future.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7583, Anodizing of aluminium and its alloys — Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7583 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 http://www.iso.org/obp
3.1
abrasive wear
wear process of a material caused by cutting or scratching actions of hard bodies or hard particles
[SOURCE: ISO 4378-2:2017, 3.3.1.2]
3.2
adhesive wear
wear process due to adhesion and extraction of material out of the body surface
[SOURCE: ISO 4378-2:2017, 3.3.1.3]
3.3
accelerated test
test undertaken under conditions designed to speed material deterioration
[SOURCE: ISO 23936-2:2011, 3.1.1]
3.4
architectural applications
external and internal building applications for coated aluminium products where both appearance and
long life are important
3.5
coating
covering on a substrate, which has protective, decorative or specific technical properties
3.6
coil coating
coating process whereby the coating material is applied continuously to a coil of metal which may be
rewound after the film has dried
[SOURCE: ISO 4618:2014, 2.56]
3.7
designer
person or organization responsible for stating the form and specification of a building or parts of a
building
3.8
durability
ability of a coating to withstand fabrication and installation procedures and a service environment
without excessive degradation of the decorative and other specific properties of the finish
3.9
inorganic coating
coating (3.5) of a coated product consisting primarily of inorganic, non-metallic material
3.10
organic coating
coating (3.5) of a coated product consisting primarily of organic material
3.11
paint
liquid or powder containing pigments, which, when applied to a substrate, forms a film having
protective, decorative or specific technical properties
[SOURCE: ISO 4618:2014, 2.184, modified — The definition has been changed so that it is restricted to
liquid and powder coating materials and not to opaque films.]
3.12
simulation
use of a similar or equivalent system to imitate a real system so that it behaves like or appears to be the
real system
[SOURCE: ISO 16781:2013, 2.9]
3.13
sol-gel processing
conversion of a chemical solution or colloidal suspension (sol) to an integrated network (gel) which can
then be further densified
[SOURCE: ISO/TS 80004-8:2013, 6.4.5]
3.14
time-of-wetness
period during which a surface is covered by adsorptive and/or liquid films of aqueous solution
[SOURCE: ISO 9223:2012, 3.5, modified — The definition has been generalized so as not to be specific to
metals and corrosion.]
2 © ISO 2017 – All rights reserved

3.15
underfilm corrosion
corrosion of a metal surface taking place beneath a coating
EXAMPLE Filiform corrosion and the corrosion that can occur beneath blistering.
3.16
visible defect
unacceptable physical imperfection or flaw in the surface coating detracting from the specified
reference material or from the product’s functions
[SOURCE: ISO 16348:2003, 2.4]
4 General
4.1 Selection of methods to protect metals against corrosion
ISO 11303:2002 gives guidelines for the selection of methods of protection against the atmospheric
corrosion of metals and alloys. It is applicable for technical equipment and products made of structural
metals, including aluminium alloys, and used under atmospheric conditions. It identifies the main
considerations in the decision-making process:
— the structural metal;
— the design of the structural element;
— the active agent, e.g. chloride ions;
— the condition of action, e.g. ambient temperature.
It uses the atmospheric corrosion classification of ISO 9223:2012. The principal factor in the selection
process is the service life of the component or product, which is derived in relation to its most important
functional property, e.g. colour.
This document is concerned with aluminium alloys as the structural metal, although it gives no
guidance on alloy selection. The design of the structural element is also outside its scope. It is concerned
with the selection of coatings depending on the active agents and conditions of action in atmospheric
environments with regard to functional properties. However, it includes no quantitative information
that relates the quality degree of the coating to service life. ISO 15686-1 gives general principles of
service life planning.
4.2 System for selecting coating types for architectural applications
With reference to the guidelines of ISO 11303:2002, the following steps can be followed to select a
coating type for a specific architectural application.
— Identify active agents and conditions of activity of the environment.
— Rate the intensity of the agents. Clause 5 provides guidance for the main agents: acidic pollution, UV
(ultra-violet) radiation and chloride deposition.
— Weigh the contributions of the agents according to the conditions of activity, e.g. time-of-wetness,
ambient temperature, wet/dry cycling frequency, the frequency of cleaning or washing by rain.
— Using the information of Clause 7, select the coating types most likely to be suitable. Refer to the
specifications for coated aluminium listed in Clause 6 for more information on specific coatings.
— Eliminate any coatings on the basis of other factors such as requirements for the design of the
structural elements including colour and reflectivity, and costs.
— Undertake comparative tests to identify the coatings most suitable for the service environment. Tests
and methods of measuring performance are described in Clauses 8 and 10, while the applicability of
tests for different environments is covered in Clause 9.
5 Types of environment
A main function of the coating is to preserve the original appearance of the coated product. Thus, the
coating should not degrade so that it becomes unsightly. An example is the effect of UV radiation on
organic coatings and dyed AAO coatings, which can cause a change in appearance. Furthermore, the
coating should prevent the corrosion of the aluminium substrate. Thus, degradation of the coating, even
if it is not noticeable, can be the precursor to aluminium corrosion which can affect the appearance of
the product. Note that EN 1999-1-1:2007+A1, Eurocode 9, gives basic design rules to avoid loss of load-
bearing capacity due to corrosion for buildings and structures made of wrought aluminium alloys.
ISO 9223:2012 gives six classes of outdoor and indoor environments based on corrosivity alone.
ISO 12944-2:1998 includes the same categories but adds further examples. Table 1 gives those
categories and includes descriptions from both those standards.
The corrosivity categories of ISO 9223:2012 are defined by the first-year corrosion effects on standard
specimens of uncoated aluminium, carbon steel, zinc and copper, which are assessed in terms of the most
significant atmospheric agents influencing the corrosion of the metals and alloys. The agents considered
were the time-of-wetness, and sulfur dioxide (SO ) and chloride pollution levels. The standard includes
data defining different levels of exposure to these agents. The levels of time-of-wetness extend from not
more than 10 hours per year to more than 5 500 hours per year. The levels of SO deposition rate extend
2 2
from not more than 4 mg/(m ·d) to more than 200 mg/(m ·d). The levels of chloride deposition rate
2 2
extend from not more than 3 mg/(m ·d) to more than 300 mg/(m ·d). ISO 9223:2012 also includes data
for other important pollutants although they are not used as classification criteria.
ISO 12944-2:1998 is concerned with painted steel structures.
For the purposes of this document, the categorization of ISO 9223:2012 has certain deficiencies as
follows.
— It is based on the corrosion of uncoated metals.
— It does not fully differentiate the effect of chloride ions from other pollutants.
— It does not include acidic pollutants other than sulfur dioxide.
— It does not consider climatic variations in UV radiation.
A significant factor affecting the corrosion of some metals and particularly steel is the chloride content
of the environment. The main sources of chlorides are the sea and de-icing of roads. Airborne salinity is
strongly dependent on the variables influencing the transport inland of sea-salt, such as wind direction,
wind velocity, local topography and distance of the exposure site from the sea. Surfaces that are
sheltered and not rain-washed in marine atmospheres where chlorides are deposited and accumulated
can experience a higher corrosivity due to the presence of hygroscopic salts. Aluminium is much less
affected by chlorides than steel, unless there is associated acidity or alkalinity.
The corrosivity of an atmosphere towards metals is not necessarily comparable to its severity in
promoting the degradation of non-metallic coatings, which can affect the aesthetic properties of the
product. However, coatings can be degraded by acids and alkalis, and associated time-of-wetness. The
wetting of surfaces is caused by many factors, for example, dew, rainfall, melting snow, a high humidity
level and condensation. Chemicals from the atmosphere can dissolve in surface films of water and
become more concentrated as the water evaporates. Thus, although time-of-wetness is important, so is
wet/dry cycling. Particulates on a surface can absorb water creating a poultice with persistent wetness
depending on rain washing and drying.
4 © ISO 2017 – All rights reserved

Table 1 — Typical environments related to corrosivity categories
Corrosivity
Corrosivity Outdoor Indoor
category
C1 Very low Dry- or cold-zone atmospheric Heated spaces with low relative
environment with very low pollution and humidity (RH) and insignificant
time-of-wetness. pollution.
EXAMPLE  Certain deserts, central EXAMPLE  Offices, shops, schools,
Arctic/Antarctica. hotels, museums.
C2 Low Temperate-zone atmospheric Unheated spaces with varying
environment with low pollution. temperature and RH. Low frequency of
condensation and low pollution.
EXAMPLE  Rural areas, small towns.
EXAMPLE  Depots, sports halls.
Dry- or cold-zone atmospheric
environment with short time-of-wetness.
EXAMPLE  Deserts, subarctic areas.
C3 Medium Temperate-zone atmospheric Spaces with moderate frequency of
environment with medium pollution or condensation and moderate pollution
some effect of chlorides. from production processes.
EXAMPLE  Urban areas, coastal areas EXAMPLE  Food-processing plants,
with low deposition of chlorides. laundries, breweries, dairies.
Subtropical- and tropical-zone
atmosphere with low pollution.
C4 High Temperate-zone atmospheric Spaces with high frequency of
environment with high pollution or condensation and high pollution from
substantial effect of chlorides. production processes.
EXAMPLE  Polluted urban areas, EXAMPLE  Chemical plants, swimming
industrial areas, coastal areas without pools, coastal ship and boatyards.
spray of salt water or exposure to strong
effect of de-icing salts.
Subtropical-zone and tropical-zone
atmosphere with medium pollution.
C5 Very high Temperate- and subtropical-zone at- Spaces with very high frequency of
mospheric environment with very high condensation and/or with high pollution
pollution and/or significant effect of from production processes.
chlorides.
EXAMPLE  Mines, caverns for
EXAMPLE  Industrial areas, coastal industrial purposes, unventilated
areas, sheltered position on coastline. sheds in subtropical and tropical zones.
CX Extreme Subtropical- and tropical-zone (very high Spaces with almost permanent conden-
time-of-wetness) atmospheric environ- sation or extensive periods of exposure
ment with very high pollution including to extreme humidity effects and/or
accompanying and production factors with high pollution from production
and/or strong effect of chlorides. processes.
EXAMPLE  Extreme industrial areas, EXAMPLE  Unventilated sheds in
coastal and offshore areas, occasional humid tropical zones with penetration
contact with salt spray. of outdoor pollution including airborne
chlorides and corrosion-stimulating
particulate matter.
The degradation of organic coatings is not only dependent on the amount of UV exposure but also
the presence of water and oxygen. Whereas atmospheric oxygen levels may not be expected to vary
significantly; time-of wetness as determined by the ambient temperature and relative humidity (RH)
can have an important effect on degradation due to UV radiation. Inorganic materials are generally
unaffected by UV radiation.
Inorganic materials can be degraded by the presence of water, particularly as an aqueous solution of
an aggressive chemical. Considering acidic pollutants, the main sources of sulfur dioxide are emissions
from industrial plants using coal or oil. Traffic is the main source of nitrogen dioxide emissions. High
levels of nitric acid are associated with high concentrations of nitrogen dioxide, organic compounds
and UV light. The decreasing sulfur dioxide levels in many parts of the world and the elevated levels of
nitrogen oxides caused by increasing traffic, together with ozone and particulates, has created a new
multi-pollutant environmental situation. In other parts of the world, in relation to the rapid development
of industry, the corrosive effect of sulfur dioxide pollution is intensifying and still dominating. Ozone is
formed in the atmosphere by interactions between sunlight, oxygen and pollutants. The concentrations
are higher in polluted rural atmospheres and lower in high-traffic urban areas. Particulates including
aerosols arise from high-concentration traffic areas and industrial activities. They can contain high
concentrations of corrosion-active components such as sulfate, nitrate and chloride anions. The burning
of coal and wood is a major source of soot. There is also diesel soot from road vehicles.
EN 1396:2015 has certain advantages over ISO 9223:2012. It is concerned with painted aluminium and
consequently categorizes end-use environments according to UV radiation intensity, as well as potential
corrosivity (see Table 2). The indices are defined in terms of the performance of variously coated test
panels during outdoor exposure testing carried out in compliance with EN 13523-19 and evaluated
according to EN 13523-21. UV radiation indices correspond to colour change and retained gloss over
two years of outdoor exposure. Corrosivity indices correspond to specific amounts of underfilm
corrosion after specific times of outdoor exposure rather than rate data for uniform corrosion as used
by ISO 9223:2012.
Table 2 — Corrosivity and UV radiation indices for different environments (EN 1396:2015)
UV radiation
Environment Corrosivity index
index (R )
uv
High UV radiation with severe conditions 3 4
Tropical (high temperature, high humidity) outdoor areas
High UV radiation outdoor areas 2 4
Very severe coastal marine (less than 3 km from the sea, depend- 3 3
ing also on the topography)
Severe industrial – extreme conditions
Rural or urban light industrial (or light marine) outdoor areas 2 3
Wet corrosive indoor areas 3 2
Dry and wet non-corrosive indoor areas 1 2
EN 1396:2015 defines the UV radiation indices geographically and on the basis of altitude as follows.
— R . Regions located north of about latitude 45 °N with an altitude not greater than 900 m.
uv2
— R . Regions located south of about latitude 45 °N and north of about latitude 37 °N with an altitude
uv3
not greater than 900 m.
— R . Regions located south of about latitude 37 °N. Every region with an altitude greater than 900 m.
uv4
Note that these criteria relate to the northern hemisphere. Because of the symmetry of the northern
and southern hemispheres, the situation is equivalent in the southern hemisphere.
It also defines coating performance requirements appropriate for each UV radiation index. This enables
the indices to be used for indoor as well as outdoor environments.
However, EN 1396:2015 includes a relatively small number of distinct categories for outdoor exposure.
There are only two each for corrosivity and UV radiation compared with the six of ISO 9223:2012 for
corrosivity alone.
The standards JIS H 8601:1999 and JIS H 8602:2010 relate specifically to anodized aluminium and
combined coatings on aluminium. They classify outdoor environments into three classes:
a) severe environment with strong UV radiation;
6 © ISO 2017 – All rights reserved

b) severe environment;
c) normal environment.
These are very broad classifications in comparison with those of Table 1.
6 Classification of coatings
6.1 Specifications for coated aluminium products
The main objectives of coating aluminium for architectural applications are to modify the appearance
of the aluminium to generate an aesthetic effect and to preserve the initial appearance of the product
over a long service life.
The following international, national and voluntary product standards specify different types of coated
aluminium.
— ISO 7599;
— ISO 28340;
— EN 1396;
— EN 12206-1;
— GB 5237.2;
— GB 5237.3;
— GB 5237.4;
— GB 5237.5;
— DIN 17611;
— JIS H 8601;
— JIS H 8602;
— BS 3987;
— BS 4842;
— AAMA 611;
— AAMA 612;
— AAMA 2603;
— AAMA 2604;
— AAMA 2605;
— GSB AL 631;
— Voluntary specification for paint coatings of architectural aluminium materials, Japan Aluminium
Products Association (JAPA), Tokyo;
— Voluntary specification for baked paint coatings of architectural aluminium alloy materials, Japan
Society for Finishing Technology (JSFT), Tokyo;
— Specifications for the QUALANOD quality label for sulphuric acid-based anodizing of aluminium,
Qualanod, Zurich;
— Specifications for a quality label for liquid and powder organic coatings on aluminium for
architectural applications, Qualicoat, Zurich.
6.2 Descriptions of coatings and coating processes
This document is cognisant of EN 15530, which gives general guidelines to standards’ writers on the
environmental aspects of aluminium products, including those for building and construction, with
their associated coating processes.
This document covers mainly paint coatings, AAO coatings and combined coatings. Other coatings
not specifically covered may include those produced by methods such as sol gel processing and
electrophoretic coating onto non-anodized aluminium. Paint coatings are generally applied by spray
deposition onto profiles while roll-coating is used most frequently to apply liquid paints onto aluminium
strip during coil coating. Combined coatings produced by the electrodeposition of organic material onto
anodized aluminium and AAO coatings are produced using immersion processes.
The production of translucent coatings can be preceded by a pretreatment to modify the appearance
of the aluminium. Such pretreatments include linishing, buffing, shot blasting, brushing, etching and
brightening.
The colouring of AAO coatings can be accomplished by dyeing with an organic or inorganic dye, or by
electrodepositing a metal into the coating that generates colour by light scattering and absorption. The
final step in an anodizing line is a sealing process that reduces the porosity and absorption capacity
of the AAO coating. Sealing processes include immersion in a demineralized-water solution at a
temperature of at least 96 °C, immersion in a special nickel fluoride-based solution at a temperature
not higher than 35 °C, exposure to steam or deposition of a sol-gel coating. The environmental impact
of these requires careful consideration, balancing the contributions of energy consumption, chemical
manufacture and effluent processing.
Pretreatment processes before the application of a paint coating are important for corrosion
protection and paint adhesion. They include anodic oxidation using sulfuric or phosphoric acid and
conversion processes using chemicals based on chromates, fluorotitanates, phosphates or silanes.
The environmental impact of hexavalent chromium is well-known and the industry is moving away
from its use. Pretreatment films are covered by the paint coating and can become exposed only when
degradation is occurring.
The organic coatings of paints and combined coatings may include inorganic components, e.g. metallic
paints. The organic materials are hydrocarbon derivatives and the coatings have to be cured, which is
an energy-intensive process.
The coatings consisting of organic materials are susceptible to the effects of UV radiation which may
degrade their appearance. AAO coatings consist mainly of aluminium oxide and hydroxide which are
unaffected although can include organic material such as dyes. As aluminium oxide and hydroxide are
amphoteric, AAO coatings are susceptible to chemical attack by acidic and alkaline solutions which
can not only degrade the appearance of the coating but reduce its thickness. There is a fundamental
difference between the materials of the different types of coating. Organic coatings resemble polymers
or plastics, while AAO and inorganic coatings have more in common with the material of rocks or glass.
AAO coatings are produced by oxidation of the aluminium so are integral with the aluminium and
perfectly adherent to it. By contrast, organic coatings are deposited onto the pretreated aluminium
surface. Conversion coatings are precipitated from solution onto the aluminium generally involving a
reaction with solvated aluminium species. Deposited coatings can lose adhesion to the aluminium.
6.3 Classifications of anodic oxidation coatings
AAO coatings are classified by the different product standards on the basis of coating thickness where
the number associated with the “AA” classification indicates the minimum average thickness in µm (see
Table 3). The higher coating thicknesses are recommended for the more aggressive conditions. This is
based on the fact that the degree of protection of the aluminium against corrosion depends primarily
8 © ISO 2017 – All rights reserved

on the thickness of the coating. However, anodizing requires significant amounts of electrical energy,
which are proportional to the coating thickness, so there is an environmental incentive not to over-
anodize. There is little effect on performance from the choice of alloy within the range of alloys used
for architectural applications. But there can be a slight deleterious effect of electrolytic colouring to
produce a dark colour. The classification does not include factors that relate to the degradation of the
AAO coating itself such as bloom formation, chalking or rate of thickness loss.
Table 3 — Classification of AAO coatings based on coating thickness
JIS H GB
Standard DIN 17611:2011 BS 3987:1991 Qualanod:2010 AAMA 611-14
8601:1999 5237.2:2008
AA25 for
especially AA25 for
AA25, AA20
aggressive outdoor use
for severe,
conditions
rugged
outdoor
AA25, AA20, AA20 for AA25, AA20,
use
AA15 for polluted outdoor AA15 for
Minimum
outdoor use conditions outdoor use
18 μm for
outdoor use
AA15 for non-
AA15 for
with periodic
polluted outdoor
Coating
outdoor
maintenance
and wet indoor
thickness
use
conditions
class
Minimum
10 μm for
indoor use or
AA10, AA6, AA10 for AA10 for dry outdoor use
AA10, AA5 for
AA5 for indoor or indoor with
indoor use
indoor use outdoor use conditions regularly
scheduled
cleaning and
maintenance
NOTE  ISO 7599:2010 uses the “AA” classification system but does not specify classes for particular applications.
6.4 Classifications of paint coatings
Paint coatings are classified by different product standards on the basis of coating quality but there is
not necessarily a direct correspondence between the quality classes of the different standards. Coating
quality is variously defined often in considerable detail.
EN 12206-1:2004, GB 5237.4:2008, GB 5237.5:2008 and BS 4842:1984 include no classification of
coatings.
EN 1396:2015 classifies coatings into four levels:
— category 1 for further painting after fabrication;
— category 2 for the following interior applications: dry and wet non-corrosive areas; wet corrosive
areas;
— category 3 for the following exterior applications: rural; or urban or light industrial (or mild marine);
tropical (high temperatures, high humidity); high UV;
— category 4 for the following applications: severe industrial — extreme conditions; very severe
coastal marine (less than 3 km from the sea, depending also on the landscape); high UV plus severe
conditions (tropical and marine).
JAPA 2010 has three categories based on the severity of the environment.
JSFT 2005 has two categories determined by the resin of the coating material.
The Qualicoat classification is based on the performance of classes 1, 2 and 3 over one, three and ten
years respectively of South Florida exposure and a wide range of laboratory tests including mechanical,
chemical, corrosion and artificial weathering, as well as coating thickness measurement. The outdoor
exposure performance is assessed by measuring gloss retention and colour change.
GSB’s classification is similar to that of Qualicoat, except the South Florida exposure periods are
2 2 2
determined by specific amounts of UV radiation, i.e. 300 MJ/m , 840 MJ/m and 1 400 MJ/m over
approximately one, three and five years respectively. It also includes an additional classification based
on underfilm corrosion occurring over three years exposure to industrial, maritime climatic conditions
preferably at Hoek van Holland.
AAMA also classifies coatings according to South Florida exposure performance and mechanical,
chemical and corrosion laboratory tests. It requires the different classes of coatings to be subjected to
one, five and ten year exposure and assesses performance by colour change, gloss retention, chalking
and erosion (thickness loss).
6.5 Classifications of combined coatings
Combined coatings are also classified by the different product standards on the basis of coating quality,
but there is not necessarily a direct correspondence between the quality classes of the different
standards.
ISO 28340:2013 specifies four quality classes.
GB 5237.3:2008 specifies two classes: “A” for use in severe environments; “B” and “S” for use in ordinary
environments.
JIS H 8602:2010 has four levels: “A1” for use in marine environments with much UV radiation; “A2”
for use in marine environments; “B” for use in ordinary environments; “C” for indoor use. Note the
emphasis on UV radiation which can affect the organic coating and marine environments where salt
can promote corrosion of the aluminium substrate.
AAMA 612 includes no classification of coatings.
6.6 Comparison of the classifications
There is a significant difference between the classification of AAO coatings and organic coatings and
even subtle differences between the systems for organic coatings. AAO coatings are classified by
perceived levels of corrosion protection provided by different thickness coatings but without clear
relationships to weathering conditions. Resistance to UV radiation is the main criterion for organic
coatings, although resistance to underfilm corrosion is sometimes included. Both of these are assessed
from outdoor exposure tests.
7 Coating selection for different environments
Clause 5 reveals the difficulties in classifying atmospheres in relation to their ability to degrade coated
aluminium. However, for the purposes of this document, a guideline system can be achieved where
the three agents UV radiation, acid pollution and chloride levels are taken separately for anodized
aluminium.
Clause 6 provides guidance on the classification of coatings. However, direct comparability is possible
only for AAO coatings because all the classifying systems use coating thickness as the determining
criterion. The criteria vary for paint coatings so the guideline system for such coatings cannot be well
defined.
Guidelines for the selection of coatings are given in Tables 4 and 5 with further descriptions below.
These guidelines assume that the coatings conform to a product specification for that particular quality
class and receive optimum in-service maintenance (see Annex A), which can lead to a service life in
excess of 20 years. Tables 4 and 5 give the minimum quality level for particular environments. It has to
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be stressed that the information of Tables 4 and 5 only contain guidance because it is not supported by
objective evidence.
The AAO coating should be selected with particular regard to the most significant single agent at the
outdoor location (see Table 4). However, consideration should also be given to the conditions of action.
UV radiation has no effect on clear anodic oxidation coatings.
Table 4 — Guidelines on the selection of the minimum thickness class of anodic oxidation
coating subject to different levels of single environmental agents
Single agent Anodic oxidation coatings
(classified by AA class)
Pollution (outdoor or indoor)
Extreme industrial areas AA25
Polluted urban areas, industrial areas
AA20
Indoor industrial facilities with high levels of pollution from production processes
Urban areas
AA15
Indoor spaces with moderate pollution from production processes
Rural areas, small towns
AA10
Indoor spaces with low pollution
Dry and wet non-corrosive indoor areas AA5
Chloride levels (marine environments)
Coastal areas, occasional contact
...