1、Designation: D 3456 86 (Reapproved 2002)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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides guidelines for determining thesusceptibility o
3、f 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 st
4、ated 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
5、and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1006 Practice for Conducting Exterior Exposure Tests ofPaints on Wood2D 1849 Test Method for Package Stability of Paint3D 3274 Test Method for Evaluating Degree of
6、 SurfaceDisfigurement of Paint Films by Microbial (Fungal orAlgal) Growth or Soil and Dirt Accumulation23. 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 t
7、hecoating. 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
8、geo-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.
9、 Thelatter 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 microbiologi
10、cal 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 represe
11、nts 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 th
12、e surface 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 Condition
13、ing 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
14、microorganisms 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 160F (70C). However, a recommended conditioningperiod consists of 1 year at room tem
15、peratures 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 March 27, 1986. Published May 1986. Originallypublished
16、as D 3456 75. Last previous edition D 3456 75 (1981)e1.2Annual Book of ASTM Standards, Vol 06.01.3Annual Book of ASTM Standards, Vol 06.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.125F (50C) as in Test Method D 1849. The condi
17、tioning ofcoatings prior to testing shall be agreeable to the producer andthe user in the case of a referee test.5.2 Preparation of Coatings for ApplicationPrior to ap-plication of the various coatings to be included in the total paintsystem, thoroughly reconstitute each coating by appropriatemixing
18、 or shaking. At the time of application, there must be nosettling, incompatibility, or other stability problem observablein the coating 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 fi
19、lm thickness. The presenceand thickness of different coatings in the complete system canhave a pronounced effect on the degree of microbiologicaldiscoloration that will occur. Thus, each paint in the systemmust be applied as recommended by the manufacturer. It isimportant that the procedure and the
20、user agree on the type ofcoatings and the spreading rate of each coating in the final testfilm. 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 coatsand no less than 7 days and not
21、longer than 1 month prior to theexterior exposure. Industrial and industrial maintenance coat-ings may require a different practice that 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
22、beingused, expose at least duplicate panels. When more than onesubstrate is employed for each exposure condition, duplicatepanels of each 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 us
23、er. 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 (12-in.) metal panels of various widths forexposures of industrial and industrial maintenance coatings.6. Substrates for Testing6.1 General ConsiderationsThe substr
24、ate on which apaint system is exposed can have a significant effect on thedegree of microbiological discoloration that may occur. 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 ret
25、ention of availablemoisture in wood surfaces. The type of metal substrate canhave either an adverse or beneficial influence on the growth offungi and algae. Some metals can inactivate certain microbio-cides, thereby allowing greater microbiological discoloration.It should also be recognized that met
26、als may also reduce thegrowth of microorganisms because of toxic compounds result-ing from weathering of the metal. Masonry surfaces generallyinhibit microbiological growth because of their alkaline nature.However, this same characteristic can contribute to microbio-logical discoloration by hydrolyz
27、ing alkali-sensitive microbio-cides that may have been used in the coating. The recom-mended substrates for testing coatings for resistance todiscoloration by microorganisms vary according to the in-tended use of the coatings. In referee cases, the substrate fortesting shall be mutually agreeable to
28、 the producer and the user.Industrial coatings should be evaluated on the surface forwhich they are designed. Trade sales and industrial 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
29、 recommended for theindicated reasons.6.2 Wood SubstratesSapwood of pine and fir generally isconsidered conducive to growth of microorganisms. This maybe due to nutrients in the wood and to the low dimensionalstability, resulting in microcracking of coatings applied on thewood with subsequent mold g
30、rowth in these cracks. Plywood,hardboard, and other wood-derived products support varyingdegrees of fungal growth depending on the nutrient value,degree of moisture absorption, and dimensional stability of thebase material. Redwood tends to have better dimensionalstability and otherwise has insignif
31、icant effect on the micro-biological growth on coatings applied over it. Cedar lumbergenerally contains compounds that aid in resisting microbio-logical growth. Both cedar and redwood contain coloredextractives that can bleed through coatings to discolor thesurface. Some of these extractives can als
32、o be nutrients thatcontribute to microbiological growth, resulting in added dis-coloration.6.3 Metal SubstratesIron, galvanized steel, and aluminumare common substrates for paints. Iron and zinc compoundsgenerally inhibit microbiological growth. On the other hand,these metals may react with certain
33、microbiocides to reduce themicrobiological inhibition. Certain microbiocides can alsocause discolored corrosion products or loss of adhesion by thecoating on these surfaces. Aluminum is rather chemically inertand does not itself promote microbiological growth. It may,however, cause loss of microbiol
34、ogical resistance of coatingscontaining certain mercury compounds because of the amal-gamation reaction by aluminum and mercury. This can result inloss of adhesion.6.4 Masonry SubstratesThe extremes of masonry sur-faces generally consist of two conditions: fresh surfaces, whichare relatively alkalin
35、e and free of fungi and algae, andweathered surfaces that are less alkaline and may be discoloredbecause of microbiological growth. Weathered masonry sur-faces represent useful test surfaces since microbiologicalcontamination can grow through inadequately preserved coat-ings from the underside. Weat
36、hered masonry surfaces also offera relatively uniform surface from panel to panel. Such unifor-mity is useful in statistically determining the relative effective-ness of various coatings or of various wash solutions forcleaning or “sterilizing” a surface before repainting. Exposuresof coatings on bo
37、th clean masonry panels and weathered panelscan provide useful results and both are recommended as testsubstrates.6.5 Moldy “Mildewed” Repaint SurfacesWeathered paintfilms that are discolored by microbiological growth are alsouseful in determining the efficacy of wash solutions to cleanor“ sterilize
38、” an old paint film prior to repainting. Such moldyrepaint surfaces also are useful in determining the resistance ofa coating system to discoloration due to microorganismsgrowing through the paint system from the underside.D 3456 86 (2002)27. Arrangement of Coated Panels on Exterior TestFences7.1 Pa
39、int systems should offer long-term resistance to mi-crobiological growth both in completely exposed areas and inshady, protected areas. Where sunlight and moisture are inabundance, chalking will occur. However, chalking is slow tooccur in shady areas. Thus, an effective microbiocide for acoating mus
40、t have long-term light stability, heat resistance, andbe sufficiently soluble and toxic to cause microbiologicalinhibition, and it must have limited solubility or leachabilityfrom the coating system such that it remains in the system forsufficiently long periods of time. Ideally, it should not induc
41、echalking for cleaning of the surface, since such chalking willcause fading or tinted paints.7.2 The most realistic conditions of exposure can best berealized on the exterior of houses. Unfortunately, buildingswith the various substrates and located in desirable localitiesand geographic locations ar
42、e seldom available. However,comparisons of various coating systems can be made byexposing coated panels on exterior test fences. Positions ofexposure should vary to include completely exposed weather-ing conditions and also protection from weathering. Theexposed conditions are useful in determining
43、the influence oftemperature, sunlight, moisture, various substrates, and subse-quent chalking on a coating. The protected, shady exposuresare useful in determining the relative microbiological inhibi-tion of coatings in the absence of chalking.7.3 Construction of test fences for protected or shadyco
44、nditions can be similar to that given in Practice D 1006 butmodified to provide for a larger test area in the protection of aneave. A protected area under an eave facing north bestrepresents the desired conditions. This eave should have aminimum of 455 mm (18 in.) overhang. The panels should beexpos
45、ed in a lapped position as would be encountered withwood siding on a house. The test area for each system shouldbegin immediately under the 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 o
46、uter 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, beginning immediately under theeave down to the bottom edge of the exposure area. Theinverted horizontal surface of the soffit under the northerlyeave is an id
47、eal test environment as well. Also, this area doesnot usually collect excessive dirt. Thus, any microbiologicaldiscoloration is readily apparent.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 o
48、f 5 (65) off vertical facingsouth. Construction should allow exposures such that moisturefalling on the test area of one panel will not drip 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
49、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 Exposure9.1 The time of the year when the initial exposure is firstmade can be critical. Because of differences in weather fromyear to year, results of exp
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