ASTM D3456-18

Standard Practice for Determining by Exterior Exposure Tests the Susceptibility of Paint Films to Microbiological Attack

SIGNIFICANCE AND USE
4.1 The growth of fungi and algae in and on the surface of paint films represents a major cause of discoloration or disfigurement of painted surfaces. This practice covers the preparation of coatings for testing, their application on substrates, and the arrangement of the coated panels on exterior test fences to determine the degree of microbiological attack that may occur on the surface of the coatings over a period of time. This practice is intended to provide guidelines for, and a discussion of, the various factors critical in selection of exterior coatings resistant to discoloration or disfigurement by algae and fungi.
SCOPE
1.1 This practice provides guidelines for determining the susceptibility of paint films to microbiological attack on exterior exposure. While it is recognized that various organisms may occur on an exposed coating, the specific types of organisms are mainly of academic interest. The degree to which microbiological discoloration occurs is the primary concern.  
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Jun-2018
• ICS: 87.040 - Paints and varnishes
• Technical Committee: D01 - Paint and Related Coatings, Materials, and Applications
• Drafting Committee: D01.28 - Biodeterioration

Relations

• Replaces: ASTM D3456-86(2012) - Standard Practice for Determining by Exterior Exposure Tests the Susceptibility of Paint Films to Microbiological Attack
• Effective Date: 01-Jul-2018
• Refers: ASTM D1849-95(2019) - Standard Test Method for Package Stability of Paint
• Effective Date: 01-Apr-2019
• Refers: ASTM D6132-13 - Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Coating Thickness Gage
• Effective Date: 01-Nov-2013
• Refers: ASTM D3274-09(2013) - Standard Test Method for Evaluating Degree of Surface Disfigurement of Paint Films by Fungal or Algal Growth, or Soil and Dirt Accumulation
• Effective Date: 01-Oct-2013
• Refers: ASTM D7091-12 - Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals
• Effective Date: 01-Apr-2012
• Refers: ASTM D3274-09 - Standard Test Method for Evaluating Degree of Surface Disfigurement of Paint Films by Fungal or Algal Growth, or Soil and Dirt Accumulation
• Effective Date: 01-Mar-2009
• Refers: ASTM D3274-09e1 - Standard Test Method for Evaluating Degree of Surface Disfigurement of Paint Films by Fungal or Algal Growth, or Soil and Dirt Accumulation
• Effective Date: 01-Mar-2009
• Refers: ASTM D6132-08 - Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Gage
• Effective Date: 01-Jul-2008
• Refers: ASTM D1849-95(2014)e1 - Standard Test Method for Package Stability of Paint
• Effective Date: 01-Jun-2008
• Refers: ASTM D1849-95(2008) - Standard Test Method for Package Stability of Paint
• Effective Date: 01-Jun-2008
• Refers: ASTM D1006-01(2006) - Standard Practice for Conducting Exterior Exposure Tests of Paints on Wood
• Effective Date: 01-Nov-2006
• Refers: ASTM D7091-05 - Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals
• Effective Date: 01-Aug-2005
• Refers: ASTM D6132-04 - Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Gage
• Effective Date: 01-Jun-2004
• Refers: ASTM D1849-95(2003) - Standard Test Method for Package Stability of Paint
• Effective Date: 10-May-2003
• Refers: ASTM D1006-93 - Standard Practice for Conducting Exterior Exposure Tests of Paints on Wood
• Effective Date: 10-Jun-2001

Overview

ASTM D3456-18, titled Standard Practice for Determining by Exterior Exposure Tests the Susceptibility of Paint Films to Microbiological Attack, is a key international standard developed by ASTM International. It outlines best practices for assessing how exterior paint films resist discoloration and disfigurement caused by microbiological activity, specifically the growth of fungi and algae. The standard is widely used to guide the preparation, application, exposure, and evaluation of painted samples to ensure the durability and aesthetic integrity of coatings in real-world conditions.

This practice is essential for developers, manufacturers, and users of exterior coatings, assisting in the selection and evaluation of products designed to resist microbial deterioration. ASTM D3456-18 addresses the environmental factors, test methods, and reporting requirements critical for the accurate evaluation of microbiological attack on paint films.

Key Topics

• Significance of Microbiological Resistance

  • Fungi and algae are primary contributors to surface discoloration and degradation of painted surfaces.
  • Susceptibility to microbiological growth can compromise appearance, reduce service life, and necessitate higher maintenance costs.

• Preparation and Application

  • Guidance on aging and conditioning coatings before testing to simulate storage and environmental exposure.
  • Procedures to ensure uniform film thickness and consistency during application, as application variables directly impact resistance to microbiological growth.

• Substrate Selection

  • Evaluation on various common substrates such as wood, metal, and masonry, considering their influence on microbial growth due to factors like porosity, nutrient content, and chemical properties.

• Exposure Methods

  • Use of exterior test fences to subject coated panels to real-world sunlight, moisture, and temperature variations.
  • Recommendations for both fully exposed and shaded positions to reflect a range of service environments.

• Observation and Evaluation

  • Visual inspection is the primary method for determining the degree of microbiological discoloration.
  • Ratings and periodic assessments are conducted in line with referenced ASTM methods to ensure standardized reporting.

• Critical Test Variables

  • Consideration of geographic location, atmospheric conditions (dust, pollen), exposure angle, substrate, and coating composition.

Applications

ASTM D3456-18 is applied extensively in the paint and coatings industry, especially in product development, quality control, and certification for exterior paints and coatings. Its practical value includes:

• Product Development

  • Enables manufacturers to evaluate new formulations or additives for improved resistance to microbial attack.

• Performance Comparison

  • Provides objective criteria to compare the durability of different paint systems under a variety of environmental conditions.

• Specification and Compliance

  • Paint producers, specifiers, and regulatory bodies use the standard to ensure products meet required resistance to microbiological attack in end use.

• Maintenance Planning

  • Assists facility managers and contractors in selecting coatings proven to last longer and perform well in regions with high humidity or frequent rainfall.

• Research and Innovation

  • Serves as a reference for academic and industrial research aimed at understanding and mitigating biodeterioration in surface coatings.

Related Standards

The methodology of ASTM D3456-18 references several other important ASTM standards, including:

• ASTM D1006 – Practice for Conducting Exterior Exposure Tests of Paints on Wood
• ASTM D1849 – Test Method for Package Stability of Paint
• ASTM D3274 – Test Method for Evaluating Degree of Surface Disfigurement of Paint Films by Fungal or Algal Growth, or Soil and Dirt Accumulation
• ASTM D6132 – Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Coating Thickness Gauge
• ASTM D7091 – Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals

These referenced standards provide additional guidance on specific test methods, substrate preparation, and evaluation criteria to ensure comprehensive assessment of paint film performance against microbiological attack.

Keywords: exterior paint testing, microbiological attack, paint film resistance, ASTM D3456-18, fungi and algae on paint, exterior exposure testing, coating durability, biodeterioration of coatings.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D3456 − 18
Standard Practice for
Determining by Exterior Exposure Tests the Susceptibility
of Paint Films to Microbiological Attack
This standard is issued under the fixed designation D3456; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Film Thickness of Applied Organic Coatings Using an
Ultrasonic Coating Thickness Gage
1.1 This practice provides guidelines for determining the
D7091 Practice for Nondestructive Measurement of Dry
susceptibility of paint films to microbiological attack on
Film Thickness of Nonmagnetic Coatings Applied to
exterior exposure. While it is recognized that various organ-
Ferrous Metals and Nonmagnetic, Nonconductive Coat-
isms may occur on an exposed coating, the specific types of
ings Applied to Non-Ferrous Metals
organisms are mainly of academic interest. The degree to
which microbiological discoloration occurs is the primary
3. Summary of Practice
concern.
3.1 Simple observation of a coated object subjected to
1.2 The values stated in SI units are to be regarded as the
exterior exposure is considered a practical and reliable method
standard. The values given in parentheses are for information
for determining the degree that microorganisms discolor the
only.
coating. However, this applies to a specific coated object
1.3 This standard does not purport to address all of the exposed under a given set of conditions. It should be recog-
safety concerns, if any, associated with its use. It is the nized that there are critical factors that influence the amount of
responsibility of the user of this standard to establish appro- fungal growth that may occur on the same coated object when
priate safety, health, and environmental practices and deter- exposed to other conditions. These factors include the geo-
mine the applicability of regulatory limitations prior to use. graphic location, local atmospheric conditions such as the dust
1.4 This international standard was developed in accor- and pollen content of the air, angle of exposure, degree to
dance with internationally recognized principles on standard- which the coating is subjected to weathering, effects of
ization established in the Decision on Principles for the moisture and sunlight, the substrates on which the coating is
Development of International Standards, Guides and Recom- applied, and the coatings in the paint system under test. The
mendations issued by the World Trade Organization Technical
latterfactorincludesthestabilityofthecoatingwhilepackaged
Barriers to Trade (TBT) Committee. in the container, as well as the composition of the coatings
included in the total system and the thickness of each coating
2. Referenced Documents
applied. Thus, while microorganisms occur on the surface of
the last film applied, the degree of microbiological growth that
2.1 ASTM Standards:
will occur is also influenced by the composition of the
D1006 Practice for Conducting Exterior Exposure Tests of
undercoats. All the above factors should be considered in the
Paints on Wood
selection of a coating resistant to discoloration by microorgan-
D1849 Test Method for Package Stability of Paint
isms.
D3274 Test Method for Evaluating Degree of Surface Dis-
figurement of Paint Films by Fungal or Algal Growth, or
4. Significance and Use
Soil and Dirt Accumulation
4.1 The growth of fungi and algae in and on the surface of
D6132 Test Method for Nondestructive Measurement of Dry
paint films represents a major cause of discoloration or
disfigurement of painted surfaces. This practice covers the
This practice is under the jurisdiction of ASTM Committee D01 on Paint and
preparation of coatings for testing, their application on
Related Coatings, Materials, and Applications and is the direct responsibility of
substrates,andthearrangementofthecoatedpanelsonexterior
Subcommittee D01.28 on Biodeterioration.
test fences to determine the degree of microbiological attack
Current edition approved July 1, 2018. Published July 2018. Originally approved
that may occur on the surface of the coatings over a period of
in 1975. Last previous edition approved in 2012 as D3456 – 86 (2012). DOI:
10.1520/D3456-18.
time. This practice is intended to provide guidelines for, and a
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
discussionof,thevariousfactorscriticalinselectionofexterior
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
coatings resistant to discoloration or disfigurement by algae
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. and fungi.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3456 − 18
5. Preparation and Application of Coatings wood surfaces generally support more mold and algae than do
coatings on metals or masonry surfaces. This is perhaps due to
5.1 Conditioning of Coatings Prior to Application—
some nutrients and greater porosity for retention of available
Individual coatings to be used in the paint system should be
moisture in wood surfaces. The type of metal substrate can
properly aged under suitable conditions prior to testing.
have either an adverse or beneficial influence on the growth of
Hydrolysis, amalgamation, absorption, and other physical and
fungi and algae. Some metals can inactivate certain
chemical changes that may have a profound influence on the
microbiocides, thereby allowing greater microbiological dis-
resistance of a coating to microorganisms usually increase with
coloration. It should also be recognized that metals may also
increasing temperature. It is recognized that actual storage
reduce the growth of microorganisms because of toxic com-
periods of paints prior to use may vary from one to several
pounds resulting from weathering of the metal. Masonry
years, and the peak temperature encountered may be as warm
surfaces generally inhibit microbiological growth because of
as 70°C (160°F). However, a recommended conditioning
their alkaline nature. However, this same characteristic can
period consists of 1 year at room temperatures or 1 month at
contribute to microbiological discoloration by hydrolyzing
50°C (125°F) as in Test Method D1849. The conditioning of
alkali-sensitive microbiocides that may have been used in the
coatings prior to testing shall be agreeable to the producer and
coating. The recommended substrates for testing coatings for
the user in the case of a referee test.
resistance to discoloration by microorganisms vary according
5.2 Preparation of Coatings for Application—Prior to ap-
to the intended use of the coatings. In referee cases, the
plicationofthevariouscoatingstobeincludedinthetotalpaint
substratefortestingshallbemutuallyagreeabletotheproducer
system, thoroughly reconstitute each coating by appropriate
and the user. Industrial coatings should be evaluated on the
mixing or shaking.At the time of application, there must be no
surface for which they are designed. Trade sales and industrial
settling, incompatibility, or other stability problem observable
maintenance coatings are general-purpose coatings and should
in the coating in the container.
perform on a variety of substrates. For such coatings, test
5.3 Application of Paint System—Apply each coating in the exposures on the following substrates are recommended for the
indicated reasons.
total paint system in an appropriate manner to provide a
specified and reasonably uniform film thickness. The presence
6.2 Wood Substrates—Sapwood of pine and fir generally is
and thickness of different coatings in the complete system can
considered conducive to growth of microorganisms. This may
have a pronounced effect on the degree of microbiological
be due to nutrients in the wood and to the low dimensional
discoloration that will occur. Thus, each paint in the system
stability, resulting in microcracking of coatings applied on the
must be applied as recommended by the manufacturer. It is
wood with subsequent mold growth in these cracks. Plywood,
important that the producer and the user agree on the type of
hardboard, and other wood-derived products support varying
coatings and the spreading rate of each coating in the final test
degrees of fungal growth depending on the nutrient value,
film (Note 1). The drying time between coats and the curing
degree of moisture absorption, and dimensional stability of the
time of the total system prior to exposure should also be
base material. Redwood tends to have better dimensional
specified. Recommended practice for house paint is 2 days
stability and otherwise has insignificant effect on the micro-
between coats and no less than 7 days and not longer than 1
biological growth on coatings applied over it. Cedar lumber
month prior to the exterior exposure. Industrial and industrial
generally contains compounds that aid in resisting microbio-
maintenance coatings may require a different practice that
logical growth. Both cedar and redwood contain colored
should be acceptable to the producer and the user.
extractives that can bleed through coatings to discolor the
NOTE 1—Coating thickness can be confirmed with Test Method D6132
surface. Some of these extractives can also be nutrients that
and/or Practice D7091 and may be reported in the final report if
contribute to microbiological growth, resulting in added dis-
performed.Alternatively, coating thickness can be recorded by spread rate
coloration.
(for example, grams/square cm).
6.3 Metal Substrates—Iron, galvanized steel, and aluminum
5.4 Test SurfaceArea—On each substrate use
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D3456 − 86 (Reapproved 2012) D3456 − 18
Standard Practice for
Determining by Exterior Exposure Tests the Susceptibility
of Paint Films to Microbiological Attack
This standard is issued under the fixed designation D3456; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice provides guidelines for determining the susceptibility of paint films to microbiological attack on exterior
exposure. While it is recognized that various organisms may occur on an exposed coating, the specific types of organisms are
mainly of academic interest. The degree to which microbiological discoloration occurs is the primary concern.
1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1006 Practice for Conducting Exterior Exposure Tests of Paints on Wood
D1849 Test Method for Package Stability of Paint
D3274 Test Method for Evaluating Degree of Surface Disfigurement of Paint Films by Fungal or Algal Growth, or Soil and Dirt
Accumulation
D6132 Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic
Coating Thickness Gage
D7091 Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals
and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals
3. Summary of Practice
3.1 Simple observation of a coated object subjected to exterior exposure is considered a practical and reliable method for
determining the degree that microorganisms discolor the coating. However, this applies to a specific coated object exposed under
a given set of conditions. It should be recognized that there are critical factors that influence the amount of fungal growth that may
occur on the same coated object when exposed to other conditions. These factors include the geographic location, local atmospheric
conditions such as the dust and pollen content of the air, angle of exposure, degree to which the coating is subjected to weathering,
effects of moisture and sunlight, the substrates on which the coating is applied, and the coatings in the paint system under test. The
latter factor includes the stability of the coating while packaged in the container, as well as the composition of the coatings included
in the total system and the thickness of each coating applied. Thus, while microorganisms occur on the surface of the last film
applied, the degree of microbiological growth that will occur is also influenced by the composition of the undercoats. All the above
factors should be considered in the selection of a coating resistant to discoloration by microorganisms.
This practice is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.28 on Biodeterioration.
Current edition approved Aug. 1, 2012July 1, 2018. Published August 2012July 2018. Originally approved in 1975. Last previous edition approved in 20082012 as
D3456 – 86 (2008).(2012). DOI: 10.1520/D3456-86R12.10.1520/D3456-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3456 − 18
4. Significance and Use
4.1 The growth of fungi and algae in and on the surface of paint films represents a major cause of discoloration or disfigurement
of painted surfaces. This practice covers the preparation of coatings for testing, their application on substrates, and the arrangement
of the coated panels on exterior test fences to determine the degree of microbiological attack that may occur on the surface of the
coatings over a period of time. This practice is intended to provide guidelines for, and a discussion of, the various factors critical
in selection of exterior coatings resistant to discoloration or disfigurement by algae and fungi.
5. Preparation and Application of Coatings
5.1 Conditioning of Coatings Prior to Application —Application—Individual coatings to be used in the paint system should be
properly aged under suitable conditions prior to testing. Hydrolysis, amalgamation, absorption, and other physical and chemical
changes that may have a profound influence on the resistance of a coating to microorganisms usually increase with increasing
temperature. It is recognized that actual storage periods of paints prior to use may vary from one to several years, and the peak
temperature encountered may be as warm as 70°C (160°F). However, a recommended conditioning period consists of 1 year at
room temperatures or 1 month at 50°C (125°F) as in Test Method D1849. The conditioning of coatings prior to testing shall be
agreeable to the producer and the user in the case of a referee test.
5.2 Preparation of Coatings for Application—Prior to application of the various coatings to be included in the total paint system,
thoroughly reconstitute each coating by appropriate mixing or shaking. At the time of application, there must be no settling,
incompatibility, or other stability problem observable in the coating in the container.
5.3 Application of Paint System—Apply each coating in the total paint system in an appropriate manner to provide a specified
and reasonably uniform film thickness. The presence and thickness of different coatings in the complete system can have a
pronounced effect on the degree of microbiological discoloration that will occur. Thus, each paint in the system must be applied
as recommended by the manufacturer. It is important that the procedureproducer and the user agree on the type of coatings and
the spreading rate of each coating in the final test film. film (Note 1). The drying time between coats and the curing time of the
total system prior to exposure should also be specified. Recommended practice for house paint is 2 days between coats and no less
than 7 days and not longer than 1 month prior to the exterior exposure. Industrial and industrial maintenance coatings may require
a different practice that should be acceptable to the producer and the user.
NOTE 1—Coating thickness can be confirmed with Test Method D6132 and/or Practice D7091 and may be reported in the final report if performed.
Alternatively, coating thickness can be recorded by spread rate (for example, grams/square cm).
2 2
5.4 Test Surface Area—. OnOn each substrate use a test area not less than 310 cm (48 in. ) in size. When only one type of
substrate is being used, expose at least duplicate panels. When more than one substrate is employed for each exposure condition,
duplicate panels of each substrate are not usually required. In case of a referee test, it is recommended that replication and size
of test area be agreed on between the producer and the user. Common practice in the industry is to use 152 by 915-mm (6 in.
(nominal) by 36-in.) panels for house paint exposures and to use 305-mm (12-in.) metal panels of various widths for exposures
of industrial and industrial maintenance coatings.
6. Substrates for Testing
6.1 General Considerations—The substrate on which a paint system is exposed can have a significant effect on the degree of
microbiological discoloration that may occur. Coated wood surfaces generally support more mold and algae than do coatings on
metals or masonry surfaces. This is perhaps due to some nutrients and greater porosity for retention of available moisture in wood
surfaces. The type of metal substrate can have either an adverse or beneficial influence on the growth of fungi and algae. Some
metals can inactivate certain microbiocides, thereby allowing greater microbiological discoloration. It should also be recognized
that metals may also reduce the growth of microorganisms because of toxic compounds resulting from weathering of the metal.
Masonry surfaces generally inhibit microbiological growth because of their alkaline nature. However, this same characteristic can
contribute to microbiological discoloration by hydrolyzing alkali-sensitive microbiocides that may have been used in the coating.
The recommended substrates for testing coatings for resistance to discoloration by microorganisms vary according to the intended
use of the coatings. In referee cases, the substrate for testing shall be mutually agreeable to the producer and the user. Industrial
coatings should be evaluated on the surface for which they are designed. Trade sales and industrial maintenance coatings are
general-purpose coatings and should perform on a variety of substrates. For such coatings, test exposures on the following
substrates are recommended for the indicated reasons.
6.2 Wood Substrates—Sapwood of pine and fir generally is considered cond
...