1、Designation: D 3456 86 (Reapproved 2008)Standard Practice forDetermining by Exterior Exposure Tests the Susceptibilityof Paint Films to Microbiological Attack1This standard is issued under the fixed designation D 3456; the number immediately following the designation indicates the year oforiginal ad
2、option 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 thesusceptibility of
3、 paint films to microbiological attack onexterior exposure. While it is recognized that various organ-isms may occur on an exposed coating, the specific types oforganisms are mainly of academic interest. The degree towhich microbiological discoloration occurs is the primaryconcern.1.2 The values sta
4、ted in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety a
5、nd health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1006 Practice for Conducting Exterior Exposure Tests ofPaints on WoodD 1849 Test Method for Package Stability of PaintD 3274 Test Method for Evaluating Degree of S
6、urfaceDisfigurement of Paint Films by Microbial (Fungal orAlgal) Growth or Soil and Dirt Accumulation3. Summary of Practice3.1 Simple observation of a coated object subjected toexterior exposure is considered a practical and reliable methodfor determining the degree that microorganisms discolor thec
7、oating. However, this applies to a specific coated objectexposed under a given set of conditions. It should be recog-nized that there are critical factors that influence the amount offungal growth that may occur on the same coated object whenexposed to other conditions. These factors include the geo
8、-graphic location, local atmospheric conditions such as the dustand pollen content of the air, angle of exposure, degree towhich the coating is subjected to weathering, effects ofmoisture and sunlight, the substrates on which the coating isapplied, and the coatings in the paint system under test. Th
9、elatter factor includes the stability of the coating while packagedin the container, as well as the composition of the coatingsincluded in the total system and the thickness of each coatingapplied. Thus, while microorganisms occur on the surface ofthe last film applied, the degree of microbiological
10、 growth thatwill occur is also influenced by the composition of theundercoats. All the above factors should be considered in theselection of a coating resistant to discoloration by microorgan-isms.4. Significance and Use4.1 The growth of fungi and algae in and on the surface ofpaint films represents
11、 a major cause of discoloration ordisfigurement of painted surfaces. This practice covers thepreparation of coatings for testing, their application on sub-strates, and the arrangement of the coated panels on exteriortest fences to determine the degree of microbiological attackthat may occur on the s
12、urface of the coatings over a period oftime. This practice is intended to provide guidelines for, and adiscussion of, the various factors critical in selection of exteriorcoatings resistant to discoloration or disfigurement by algaeand fungi.5. Preparation and Application of Coatings5.1 Conditioning
13、 of Coatings Prior to ApplicationIndividual coatings to be used in the paint system should beproperly aged under suitable conditions prior to testing. Hy-drolysis, amalgamation, absorption, and other physical andchemical changes that may have a profound influence on theresistance of a coating to mic
14、roorganisms usually increase withincreasing temperature. It is recognized that actual storageperiods of paints prior to use may vary from one to severalyears, and the peak temperature encountered may be as warmas 70C (160F). However, a recommended conditioningperiod consists of 1 year at room temper
15、atures or 1 month at1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.28 on Biodeterioration.Current edition approved June 1, 2008. Published June 2008. Originallyapproved in 19
16、75. Last previous edition approved in 2002 as D 3456 86 (2002).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM websit
17、e.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.50C (125F) as in Test Method D 1849. The conditioning ofcoatings prior to testing shall be agreeable to the producer andthe user in the case of a referee test.5.2 Preparation of Coati
18、ngs for ApplicationPrior to ap-plication of the various coatings to be included in the total paintsystem, thoroughly reconstitute each coating by appropriatemixing or shaking. At the time of application, there must be nosettling, incompatibility, or other stability problem observablein the coating i
19、n the container.5.3 Application of Paint SystemApply each coating in thetotal paint system in an appropriate manner to provide aspecified and reasonably uniform film thickness. The presenceand thickness of different coatings in the complete system canhave a pronounced effect on the degree of microbi
20、ologicaldiscoloration that will occur. Thus, each paint in the systemmust be applied as recommended by the manufacturer. It isimportant that the procedure and the user agree on the type ofcoatings and the spreading rate of each coating in the final testfilm. The drying time between coats and the cur
21、ing time of thetotal system prior to exposure should also be specified.Recommended practice for house paint is 2 days between coatsand no less than 7 days and not longer than 1 month prior to theexterior exposure. Industrial and industrial maintenance coat-ings may require a different practice that
22、should be acceptableto the producer and the user.5.4 . On each substrate use a test area not less than 310cm2(48 in.2) in size. When only one type of substrate is beingused, expose at least duplicate panels. When more than onesubstrate is employed for each exposure condition, duplicatepanels of each
23、 substrate are not usually required. In case of areferee test, it is recommended that replication and size of testarea be agreed on between the producer and the user. Commonpractice in the industry is to use 152 by 915-mm (6 in.(nominal) by 36-in.) panels for house paint exposures and touse 305-mm (
24、12-in.) metal panels of various widths forexposures of industrial and industrial maintenance coatings.6. Substrates for Testing6.1 General ConsiderationsThe substrate on which apaint system is exposed can have a significant effect on thedegree of microbiological discoloration that may occur. Coatedw
25、ood surfaces generally support more mold and algae than docoatings on metals or masonry surfaces. This is perhaps due tosome nutrients and greater porosity for retention of availablemoisture in wood surfaces. The type of metal substrate canhave either an adverse or beneficial influence on the growth
26、 offungi and algae. Some metals can inactivate certain microbio-cides, thereby allowing greater microbiological discoloration.It should also be recognized that metals may also reduce thegrowth of microorganisms because of toxic compounds result-ing from weathering of the metal. Masonry surfaces gene
27、rallyinhibit microbiological growth because of their alkaline nature.However, this same characteristic can contribute to microbio-logical discoloration by hydrolyzing alkali-sensitive microbio-cides that may have been used in the coating. The recom-mended substrates for testing coatings for resistan
28、ce todiscoloration by microorganisms vary according to the in-tended use of the coatings. In referee cases, the substrate fortesting shall be mutually agreeable to the producer and the user.Industrial coatings should be evaluated on the surface forwhich they are designed. Trade sales and industrial
29、mainte-nance coatings are general-purpose coatings and should per-form on a variety of substrates. For such coatings, testexposures on the following substrates are recommended for theindicated reasons.6.2 Wood SubstratesSapwood of pine and fir generally isconsidered conducive to growth of microorgan
30、isms. This maybe due to nutrients in the wood and to the low dimensionalstability, resulting in microcracking of coatings applied on thewood with subsequent mold growth in these cracks. Plywood,hardboard, and other wood-derived products support varyingdegrees of fungal growth depending on the nutrie
31、nt value,degree of moisture absorption, and dimensional stability of thebase material. Redwood tends to have better dimensionalstability and otherwise has insignificant effect on the micro-biological growth on coatings applied over it. Cedar lumbergenerally contains compounds that aid in resisting m
32、icrobio-logical growth. Both cedar and redwood contain coloredextractives that can bleed through coatings to discolor thesurface. Some of these extractives can also be nutrients thatcontribute to microbiological growth, resulting in added dis-coloration.6.3 Metal SubstratesIron, galvanized steel, an
33、d aluminumare 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 alsocause discolored corrosion products or loss of adhes
34、ion by thecoating on these surfaces. Aluminum is rather chemically inertand does not itself promote microbiological growth. It may,however, cause loss of microbiological resistance of coatingscontaining certain mercury compounds because of the amal-gamation reaction by aluminum and mercury. This can
35、 result inloss of adhesion.6.4 Masonry SubstratesThe extremes of masonry sur-faces generally consist of two conditions: fresh surfaces, whichare relatively alkaline and free of fungi and algae, andweathered surfaces that are less alkaline and may be discoloredbecause of microbiological growth. Weath
36、ered masonry sur-faces represent useful test surfaces since microbiologicalcontamination can grow through inadequately preserved coat-ings from the underside. Weathered masonry surfaces also offera relatively uniform surface from panel to panel. Such unifor-mity is useful in statistically determinin
37、g the relative effective-ness of various coatings or of various wash solutions forcleaning or “sterilizing” a surface before repainting. Exposuresof coatings on both clean masonry panels and weathered panelscan provide useful results and both are recommended as testsubstrates.6.5 Moldy “Mildewed” Re
38、paint SurfacesWeathered paintfilms that are discolored by microbiological growth are alsouseful in determining the efficacy of wash solutions to cleanor“ sterilize” an old paint film prior to repainting. Such moldyrepaint surfaces also are useful in determining the resistance ofa coating system to d
39、iscoloration due to microorganismsgrowing through the paint system from the underside.D 3456 86 (2008)27. Arrangement of Coated Panels on Exterior TestFences7.1 Paint systems should offer long-term resistance to mi-crobiological growth both in completely exposed areas and inshady, protected areas. W
40、here sunlight and moisture are inabundance, chalking will occur. However, chalking is slow tooccur in shady areas. Thus, an effective microbiocide for acoating must have long-term light stability, heat resistance, andbe sufficiently soluble and toxic to cause microbiologicalinhibition, and it must h
41、ave limited solubility or leachabilityfrom the coating system such that it remains in the system forsufficiently long periods of time. Ideally, it should not inducechalking for cleaning of the surface, since such chalking willcause fading or tinted paints.7.2 The most realistic conditions of exposur
42、e can best berealized on the exterior of houses. Unfortunately, buildingswith the various substrates and located in desirable localitiesand geographic locations are seldom available. However,comparisons of various coating systems can be made byexposing coated panels on exterior test fences. Position
43、s ofexposure should vary to include completely exposed weather-ing conditions and also protection from weathering. Theexposed conditions are useful in determining the influence oftemperature, sunlight, moisture, various substrates, and subse-quent chalking on a coating. The protected, shady exposure
44、sare useful in determining the relative microbiological inhibi-tion of coatings in the absence of chalking.7.3 Construction of test fences for protected or shadyconditions can be similar to that given in Practice D 1006 butmodified to provide for a larger test area in the protection of aneave. A pro
45、tected area under an eave facing north bestrepresents the desired conditions. This eave should have aminimum of 455 mm (18 in.) overhang. The panels should beexposed in a lapped position as would be encountered withwood siding on a house. The test area for each system shouldbegin immediately under t
46、he eave and continue down the testfence to a point at least 610 mm (2 ft) below an imaginaryhorizontal line, which is derived by projecting at a 45 anglefrom the outer edge of the eave, downward and inward to thetest panels. Thus, an 18-in. eave would require a minimum of1.06 m (3.5 ft) of test pane
47、ls, beginning immediately under theeave down to the bottom edge of the exposure area. Theinverted horizontal surface of the soffit under the northerlyeave is an ideal test environment as well. Also, this area doesnot usually collect excessive dirt. Thus, any microbiologicaldiscoloration is readily a
48、pparent.7.4 Construction of test fences for exposed conditions canbe similar to that in Practice D 1006 but modified to providefor offset panels held at an angle of 5 (65) off vertical facingsouth. Construction should allow exposures such that moisturefalling on the test area of one panel will not d
49、rip on the nextpanels below.8. Geographic Location of Test Fences8.1 The climatic and environmental conditions of the testfences should be similar to those of the areas in which the paintsystem is intended for use. For coatings to be used nationally,it is desirable to expose in warm and humid environments.Exposures should be made in both shady conditions and indirect sunlight. It should be recognized that the microfloraoccurring in different parts of a country will vary so that moldand algae encountered in one test location may not necessarilybe those of another.9. Pe
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