1、Designation: D3456 86 (Reapproved 2012)D3456 18Standard Practice forDetermining by Exterior Exposure Tests the Susceptibilityof Paint Films to Microbiological Attack1This standard is issued under the fixed designation D3456; the number immediately following the designation indicates the year oforigi
2、nal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides guidelines for determining the susceptibi
3、lity of paint films to microbiological attack on exteriorexposure. While it is recognized that various organisms may occur on an exposed coating, the specific types of organisms aremainly of academic interest. The degree to which microbiological discoloration occurs is the primary concern.1.2 The va
4、lues 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 responsibilityof the user of this standard to establish appropriat
5、e safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the
6、Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1006 Practice for Conducting Exterior Exposure Tests of Paints on WoodD1849 Test Method for Package Stabili
7、ty of PaintD3274 Test Method for Evaluating Degree of Surface Disfigurement of Paint Films by Fungal orAlgal Growth, or Soil and DirtAccumulationD6132 Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an UltrasonicCoating Thickness GageD7091 Practice
8、for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metalsand Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals3. Summary of Practice3.1 Simple observation of a coated object subjected to exterior exposure is considered a practical and reli
9、able method fordetermining the degree that microorganisms discolor the coating. However, this applies to a specific coated object exposed undera given set of conditions. It should be recognized that there are critical factors that influence the amount of fungal growth that mayoccur on the same coate
10、d object when exposed to other conditions.These factors include the geographic location, local atmosphericconditions 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
11、 coating is applied, and the coatings in the paint system under test. Thelatter factor includes the stability of the coating while packaged in the container, as well as the composition of the coatings includedin the total system and the thickness of each coating applied. Thus, while microorganisms o
12、ccur on the surface of the last filmapplied, the degree of microbiological growth that will occur is also influenced by the composition of the undercoats.All the abovefactors should be considered in the selection of a coating resistant to discoloration by microorganisms.1 This practice is under the
13、jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.28 on Biodeterioration.Current edition approved Aug. 1, 2012July 1, 2018. Published August 2012July 2018. Originally approved in 1975. Last previous editi
14、on approved in 20082012 asD3456 86 (2008).(2012). DOI: 10.1520/D3456-86R12.10.1520/D3456-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standardsstandards Do
15、cument Summary page on the ASTM website.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. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM
16、 recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Signi
17、ficance and Use4.1 The growth of fungi and algae in and on the surface of paint films represents a major cause of discoloration or disfigurementof painted surfaces. This practice covers the preparation of coatings for testing, their application on substrates, and the arrangementof the coated panels
18、on exterior test fences to determine the degree of microbiological attack that may occur on the surface of thecoatings over a period of time. This practice is intended to provide guidelines for, and a discussion of, the various factors criticalin selection of exterior coatings resistant to discolora
19、tion or disfigurement by algae and fungi.5. Preparation and Application of Coatings5.1 Conditioning of Coatings Prior to Application ApplicationIndividual coatings to be used in the paint system should beproperly aged under suitable conditions prior to testing. Hydrolysis, amalgamation, absorption,
20、and other physical and chemicalchanges that may have a profound influence on the resistance of a coating to microorganisms usually increase with increasingtemperature. It is recognized that actual storage periods of paints prior to use may vary from one to several years, and the peaktemperature enco
21、untered may be as warm as 70C (160F). However, a recommended conditioning period consists of 1 year atroom temperatures or 1 month at 50C (125F) as in Test Method D1849. The conditioning of coatings prior to testing shall beagreeable to the producer and the user in the case of a referee test.5.2 Pre
22、paration of Coatings for ApplicationPrior 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 observabl
23、e in the coating in the container.5.3 Application of Paint SystemApply each coating in the total paint system in an appropriate manner to provide a specifiedand reasonably uniform film thickness. The presence and thickness of different coatings in the complete system can have apronounced effect on t
24、he degree of microbiological discoloration that will occur. Thus, each paint in the system must be appliedas recommended by the manufacturer. It is important that the procedureproducer and the user agree on the type of coatings andthe spreading rate of each coating in the final test film. film (Note
25、 1). The drying time between coats and the curing time of thetotal system prior to exposure should also be specified. Recommended practice for house paint is 2 days between coats and no lessthan 7 days and not longer than 1 month prior to the exterior exposure. Industrial and industrial maintenance
26、coatings may requirea different practice that should be acceptable to the producer and the user.NOTE 1Coating 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 (
27、for example, grams/square cm).5.4 Test Surface Area. OnOn each substrate use a test area not less than 310 cm2 (48 in.2) in size. When only one type ofsubstrate is being used, expose at least duplicate panels. When more than one substrate is employed for each exposure condition,duplicate panels of e
28、ach substrate are not usually required. In case of a referee test, it is recommended that replication and sizeof 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 30
29、5-mm (12-in.) metal panels of various widths for exposuresof industrial and industrial maintenance coatings.6. Substrates for Testing6.1 General ConsiderationsThe substrate on which a paint system is exposed can have a significant effect on the degree ofmicrobiological discoloration that may occur.
30、Coated wood surfaces generally support more mold and algae than do coatings onmetals or masonry surfaces. This is perhaps due to some nutrients and greater porosity for retention of available moisture in woodsurfaces. The type of metal substrate can have either an adverse or beneficial influence on
31、the growth of fungi and algae. Somemetals can inactivate certain microbiocides, thereby allowing greater microbiological discoloration. It should also be recognizedthat metals may also reduce the growth of microorganisms because of toxic compounds resulting from weathering of the metal.Masonry surfa
32、ces generally inhibit microbiological growth because of their alkaline nature. However, this same characteristic cancontribute to microbiological discoloration by hydrolyzing alkali-sensitive microbiocides that may have been used in the coating.The recommended substrates for testing coatings for res
33、istance to discoloration by microorganisms vary according to the intendeduse of the coatings. In referee cases, the substrate for testing shall be mutually agreeable to the producer and the user. Industrialcoatings should be evaluated on the surface for which they are designed. Trade sales and indus
34、trial maintenance coatings aregeneral-purpose coatings and should perform on a variety of substrates. For such coatings, test exposures on the followingsubstrates are recommended for the indicated reasons.6.2 Wood SubstratesSapwood of pine and fir generally is considered conducive to growth of micro
35、organisms. This may bedue to nutrients in the wood and to the low dimensional stability, resulting in microcracking of coatings applied on the wood withsubsequent mold growth in these cracks. Plywood, hardboard, and other wood-derived products support varying degrees of fungalgrowth depending on the
36、 nutrient value, degree of moisture absorption, and dimensional stability of the base material. Redwoodtends to have better dimensional stability and otherwise has insignificant effect on the microbiological growth on coatings appliedover it. Cedar lumber generally contains compounds that aid in res
37、isting microbiological growth. Both cedar and redwood containcolored extractives that can bleed through coatings to discolor the surface. Some of these extractives can also be nutrients thatcontribute to microbiological growth, resulting in added discoloration.D3456 1826.3 Metal SubstratesIron, galv
38、anized steel, and aluminum are common substrates for paints. Iron and zinc compoundsgenerally inhibit microbiological growth. On the other hand, these metals may react with certain microbiocides to reduce themicrobiological inhibition. Certain microbiocides can also cause discolored corrosion produc
39、ts or loss of adhesion by the coatingon these surfaces.Aluminum is rather chemically inert and does not itself promote microbiological growth. It may, however, causeloss of microbiological resistance of coatings containing certain mercury compounds because of the amalgamation reaction byaluminum and
40、 mercury. This can result in loss of adhesion.6.4 Masonry SubstratesThe extremes of masonry surfaces generally consist of two conditions: fresh surfaces, which arerelatively alkaline and free of fungi and algae, and weathered surfaces that are less alkaline and may be discolored because ofmicrobiolo
41、gical growth. Weathered masonry surfaces represent useful test surfaces since microbiological contamination can growthrough inadequately preserved coatings from the underside. Weathered masonry surfaces also offer a relatively uniform surfacefrom panel to panel. Such uniformity is useful in statisti
42、cally determining the relative effectiveness of various coatings or of variouswash solutions for cleaning or “sterilizing” a surface before repainting. Exposures of coatings on both clean masonry panels andweathered panels can provide useful results and both are recommended as test substrates.6.5 Mo
43、ldy “Mildewed” Repaint SurfacesWeathered paint films that are discolored by microbiological growth are also usefulin determining the efficacy of wash solutions to clean or“ sterilize”or “sterilize” an old paint film prior to repainting. Such moldyrepaint surfaces also are useful in determining the r
44、esistance of a coating system to discoloration due to microorganisms growingthrough the paint system from the underside.7. Arrangement of Coated Panels on Exterior Test Fences7.1 Paint systems should offer long-term resistance to microbiological growth both in completely exposed areas and in shady,p
45、rotected areas. Where sunlight and moisture are in abundance, chalking will occur. However, chalking is slow to occur in shadyareas. Thus, an effective microbiocide for a coating must have long-term light stability, heat resistance, and be sufficiently solubleand toxic to cause microbiological inhib
46、ition, and it must have limited solubility or leachability from the coating system such thatit remains in the system for sufficiently long periods of time. Ideally, it should not induce chalking for cleaning of the surface, sincesuch chalking will cause fading or tinted paints.7.2 The most realistic
47、 conditions of exposure can best be realized on the exterior of houses. Unfortunately, buildings with thevarious substrates and located in desirable localities and geographic locations are seldom available. However, comparisons ofvarious coating systems can be made by exposing coated panels on exter
48、ior test fences. Positions of exposure should vary toinclude completely exposed weathering conditions and also protection from weathering. The exposed conditions are useful indetermining the influence of temperature, sunlight, moisture, various substrates, and subsequent chalking on a coating. Thepr
49、otected, shady exposures are useful in determining the relative microbiological inhibition of coatings in the absence of chalking.7.3 Construction of test fences for protected or shady conditions can be similar to that given in Practice D1006 but modifiedto provide for a larger test area in the protection of an eave.Aprotected area under an eave facing north best represents the desiredconditions. This eave should have a minimum of 455 mm (18 in.) overhang. The panels should be exposed in a lapped positionas would be encountered with wood siding on a house. The test
