1、Designation: D3456 86 (Reapproved 2012)Standard 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 oforiginal adop
2、tion 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 p
3、aint 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 state
4、d 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 and
5、 health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1006 Practice for Conducting Exterior Exposure Tests ofPaints on WoodD1849 Test Method for Package Stability of PaintD3274 Test Method for Evaluating Degree of Surfac
6、e Dis-figurement of Paint Films by Fungal or Algal Growth, orSoil 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 thecoating. Howeve
7、r, 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-graphic locat
8、ion, 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. Thelatter factor
9、 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 growth thatwi
10、ll 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 a major cause
11、 of discoloration ordisfigurement of painted surfaces. This practice covers thepreparation of coatings for testing, their application onsubstrates, and the arrangement of the coated panels on exteriortest fences to determine the degree of microbiological attackthat may occur on the surface of the co
12、atings 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 of Coatings Pri
13、or to ApplicationIndividual coatings to be used in the paint system should beproperly aged under suitable conditions prior to testing.Hydrolysis, amalgamation, absorption, and other physical andchemical changes that may have a profound influence on theresistance of a coating to microorganisms usuall
14、y 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 temperatures or 1 month
15、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 Aug. 1, 2012. Published August 2012. Originallyapproved in 1975. Last previou
16、s edition approved in 2008 as D3456 86 (2008).DOI: 10.1520/D3456-86R12.2For 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 AST
17、M website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States150C (125F) as in Test Method D1849. 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
18、 Coatings 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 coa
19、ting in 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 m
20、icrobiologicaldiscoloration 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 t
21、he curing 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
22、 that should be acceptableto the producer and the user.5.4 . On each substrate use a test area not less than 310 cm2(48 in.2) in size. When only one type of substrate is being used,expose at least duplicate panels. When more than one substrateis employed for each exposure condition, duplicate panels
23、 ofeach substrate are not usually required. In case of a referee test,it is recommended that replication and size of test area beagreed on between the producer and the user. Common practicein the industry is to use 152 by 915-mm (6 in. (nominal) by36-in.) panels for house paint exposures and to use
24、305-mm(12-in.) metal panels of various widths for exposures ofindustrial 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.
25、Coatedwood 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
26、 growth offungi and algae. Some metals can inactivate certainmicrobiocides, thereby allowing greater microbiological dis-coloration. It should also be recognized that metals may alsoreduce the growth of microorganisms because of toxic com-pounds resulting from weathering of the metal. Masonrysurface
27、s generally inhibit microbiological growth because oftheir alkaline nature. However, this same characteristic cancontribute to microbiological discoloration by hydrolyzingalkali-sensitive microbiocides that may have been used in thecoating. The recommended substrates for testing coatings forresistan
28、ce to discoloration by microorganisms vary accordingto the intended use of the coatings. In referee cases, thesubstrate for testing shall be mutually agreeable to the producerand the user. Industrial coatings should be evaluated on thesurface for which they are designed. Trade sales and industrialma
29、intenance coatings are general-purpose coatings and shouldperform 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 microorganisms.
30、 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 nutrient va
31、lue,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 microb
32、io-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, and alu
33、minumare 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 adhesion b
34、y 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 amalga-mation reaction by aluminum and mercury. This can resu
35、lt inloss of adhesion.6.4 Masonry SubstratesThe extremes of masonry surfacesgenerally consist of two conditions: fresh surfaces, which arerelatively alkaline and free of fungi and algae, and weatheredsurfaces that are less alkaline and may be discolored because ofmicrobiological growth. Weathered ma
36、sonry surfaces representuseful test surfaces since microbiological contamination cangrow through inadequately preserved coatings from the under-side. Weathered masonry surfaces also offer a relatively uni-form surface from panel to panel. Such uniformity is useful instatistically determining the rel
37、ative effectiveness of variouscoatings or of various wash solutions for cleaning or “steriliz-ing” a surface before repainting. Exposures of coatings on bothclean masonry panels and weathered panels can provide usefulresults and both are recommended as test substrates.6.5 Moldy “Mildewed” Repaint Su
38、rfacesWeathered 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 ofD3456 86 (2012)2a coating sys
39、tem to discoloration due to microorganismsgrowing through the paint system from the underside.7. 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. Where sunl
40、ight 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 have limit
41、ed 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 exposure can bes
42、t 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. Positions ofexpos
43、ure 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 exposuresare usef
44、ul 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 D1006 butmodified to provide for a larger test area in the protection of aneave. A protected are
45、a 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 the eave an
46、d 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 panels, beginn
47、ing 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 apparent.7.
48、4 Construction of test fences for exposed conditions canbe similar to that in Practice D1006 but modified to provide foroffset 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 drip on the
49、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. Periods of Ex
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