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wood and masonry, the coating has to allow moderate amounts of water vapor to pass through the film without damage to it. Hence, the water vapor transmission characteristics of coatings are important in assessing their performance in practical use. 5.2The purpose of these test methods is to obtain values of water vapor transfer through coatings that range in permeabil-ity from high to low. These values are for use in design, manufacture, and marketing.5.3The water vapor transmission is not a linear function of film thickness, temperature or relative humidity.5.4Values of water vapor transmission rate (WVTand water vapor permeance (WVPcan be used in the relative rating of coatings only if the coatings are tested under the same closely controlled conditions of temperature and relative hu-midity, and if their thicknesses are equal.5.5Test Method A The Dry Cup Method is the preferred test method for obtaining values that relate to conventional dwellings where high relative humidities are not anticipated. 5.6Test Method B The Wet Cup Method is the preferred test method for obtaining values that relate to applications where high relative humidities are anticipated in the vicinity of the barrier material. In general, the more permeable a coating is to the passage of moisture as is typical of many water-reducible coatings, the greater its affinity for water and the greater the increase in transmission when tested in and exposed to high humidities. Absorption of water may make a coating less dense, thus allowing moisture to diffuse easily and cause a much higher moisture vapor transmission rate, (WVTRthan would occur in drier environments.6. Apparatus6.1Perm Cup or Dish , consisting of a container made of a noncorroding material, impermeable to water or water vapor. If the cup or dish is made of aluminum, it must be anodized or given a protective clear coating to prevent corrosion. 6.1.1One type of cup that is suitable has a flanged edge and is equipped with a separate corresponding flange, so that the test specimen can be held between them. The contacting faces of the flanges shall be ground to such flatness that when the film is in position, moisture transfer can occur only through the exposed film area. For hard films, or films having a very rough surface, a soft rubber gasket may be inserted between the film and the flange. The flanges shall then be held together with suitable clamps.6.1.2Another suitable cup is any open circular or rectangu-lar dish to which the test film can be sealed with wax or sealant. 6.2Test Chamber , with a controlled temperature and rela-tive humidity as specified in Section 4. Air shall be circulated throughout the chamber to maintain uniform conditions at all test locations. For low or high humidity conditions, a standard desiccator or other suitable cabinet may be used. For maintain-ing constant relative humidity by means of aqueous solutions, refer to procedures outlined in Practice E 104.6.3Analytical Balance , having an adequate capacity for the weight of the test cups and a sensitivity of 1mg.7. Reagents and Materials7.1Purity of Water Unless otherwise indicated, reference to water shall be understood to mean reagent water conforming to Type IV of Specification D 1193.7.2Desiccant , consisting of either anhydrous calcium chlo-ride (CaCL2 or anhydrous magnesium perchlorate (Mg-(CLO4 2. The calcium chloride should be dried at 400F (200Cbefore use. If calcium chloride will react with the test specimen, an adsorbing desiccant such as a silica gel may be used but the moisture gain by this desiccant during the test must be limited to 4%.Use caution in handling magnesium perchlorate because of possible chemical reaction that may be produced if it comes in contact with some organic materials and is subsequently heated to regenerate the anhydrous salt. 7.3Sealant , such as wax for attaching the test specimen to the top of the perm cup or dish. It must be highly resistant to the passage of water vapor. It must not lose weight to, or gain weight from, the atmosphere in an amount, over the required period of time, that would affect the test results by more than 2%.It must not affect the vapor pressure in a water-filled dish. N OTE 1Among acceptable sealants are (1 a 60:40mixture of microcrystalline wax and refined crystalline parafin wax, (2 tissue embedding wax, and (3 a 50:50mixture of beeswax and rosin. 7.4Release Paper , prepare free films, whenever possible to eliminate the potential interference of substrates, on release paper 5or glass substrates following procedures outlined in Practice D 4708.7.5Film Support , for preparing films that are too brittle or otherwise unsatisfactory for handling as free films. Support materials such as paper charts, 6filter paper, and glass cloth have been found satisfactory in some instances. Such support can have an effect on the test results.8. Test Specimens8.1It is very important that the test specimens be smooth, and completely continuous films of uniform thickness through-out the test area. Apply air drying coatings to substrates using one of the methods described in Practices D 823or D 4708. N OTE 2 Special test conditions may require that the coating be applied by brushing, roller coating or other special methods. The thickness of the coating applied shall be within normal range for the type of material under test, and shall not vary by more than 5%of the total thickness in any test series.N OTE 3When applying baking finishes, bake for specified time and temperature in accordance with manufacturers5 instructions. Permeance may vary with the baking schedule or the time of air drying.8.2Air dry the coated material in a horizontal position for 7 days in a room preferably maintained at 73.563.5F(236 2Cand 5065%relative humidity. If the material is to be tested as a free film, remove it from the substrate and allow the p reviously unexposed surface to dry for an additional 7days. The drying schedule may be modified as recommended by manufacturer.5The sole source of supply of release Paper, Form RP-1K, known to the committee at this time is the Leneta Co., 15Whitney Rd., Mahwah, NJ 07430. If you are aware of alternative suppliers, please provide this information to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsi ble technical committee, 1which you may attend.6The sole source of supply of paper charts, Form NWK, known to the committee at this time is the Leneta Co., 15Whitney Rd., Mahwah, NJ 07430. If you are aware of alternative suppliers, please provide this information to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsi ble technical committee, 1which you mayattend.N OTE 4一Examine test films for the presence of pinholes or other defects before commencing the test. It may be advisable to apply the test material in two coats, applying the second coat perpendicular to the first coat and allowing for an adequate drying period between coats to achieve the desired film thickness.8.3Measure the thickness of the test specimen in several places with a micrometer using procedures in Test Methods D 1005to ensure a uniform thickness.8.4When coatings are applied to support materials, the coated side of the test specimen should be placed away from the desiccant or towards the water in the cup, depending upon the service environment. Coatings should not be applied to both sides of a support. Glass cloth is preferred for coatings that are cured by baking.TEST METHOD ADRY CUP METHOD 9. Test Conditions9.1Unless other conditions are agreed upon between the purchaser and the seller, the tests shall be performed under one or more of the following conditions:9.1.1Condition A Test chamber or cabinet maintained at 7361F(2360.6Cand 5062%relative humidity. 9.1.2Condition B Test chamber or desiccator maintained at 10061F(3860.6Cand 9062%relative humidity. 10. Procedure10.1Prepare at least three perm cups or dishes for each test material as follows:10.1.1Fill the cups with desiccant to within 1/ 4in. (6mm of the top edge.10.1.2If the cups are equipped with flanges, place the test specimen between the flanges and adjust the clamps to hold it firmly in position.10.1.3If the cups are not equipped with flanges, seal the test specimen to the top edge of the cups with wax as follows: 10.1.3.1First carefully place the test specimen, cut to the size of the frame, on a thin cardboard ring soaked in molten wax.10.1.3.2Then place the specimen-covered frame over the mouth of the cup. Thoroughly seal the frame to the edge of the cup at the temperature to be used in the test. If the coating is on a substrate or support, place the coated side away from the desiccant in the cup.N OTE 5Imperfections in the film that are not readily visible may produce inconsistent results; consequently make sure that the test is always run at least in triplicate.10.2Weigh the loaded cups to 1mg and if a test chamber is not being used, place them in the test cabinets or desiccators. Record time, temperature, and relative humidity. 10.3Remove if necessary, the cups for periodic weighing to determine weight gain. Coatings expected to have high WVT ratings, over 10perms, may require weighings more frequently than once a day.10.4In general, weigh the cups every 24h for a period of 3 weeks, or until the weight change versus time becomes constant. Record the time that weighings are taken to the precision of approximately 1%of the time span between weighings. Thus, if weighings are made every day, a time to the nearest 15minutes would be allowed.10.5Shake cups containing desiccant everyday to prevent surface saturation of the material. If moisture absorbed by the desiccant exceeds 20%of the desiccant weight, discontinue the test.10.6Return the cups to the test chamber immediately after weighing.TEST METHOD BWET CUP METHOD11. Test Conditions11.1Unless other conditions are agreed upon between the purchaser and the seller, perform the test(sunder one or more of the following conditions:11.1.1Condition A Test chamber or cabinet maintained at 7361F(2360.6Cand 5062%relative humidity. 11.1.2Condition C Test chamber or desiccator maintained at 7361Fand very low (nearzero relative humidity. 12. Procedure12.1Prepare at least three cups for each test material as follows:12.1.1Fill the cups with water to within 1/ 4in. (6mm of the top edge.12.1.2If the cups are equipped with flanges, place the test specimen over the opening of the cups between the flanges and adjust the clamps to hold them firmly in position. If the coating is on a substrate or support, place the coated side towards the water in the cups.12.1.3If the cups are not equipped with flanges, seal the test specimens to the top edge of the cups with wax in accordance with procedures in 10.1.3.1and 10.1.3.2. If the coating is on a substrate or support, place the coated side towards the water in the cup.12.2Weigh the loaded cups to 1mg and place them in the test chamber. Record time, temperature and relative humidity. Follow procedures outlined in 10.5and 10.6.12.3Return the cups to the test chamber immediately after weighings.13. Calculations13.1For each material tested, plot the weight change against elapsed time. When a straight line adequately fits the plot of at least four properly spaced points, a nominally steady state exists and the slope of the straight line is the rate of water vapor transmission.13.2Calculate one or more of the following, depending on the water vapor transmission characteristics to be determined: 13.2.1Calculate the water vapor transmission rate, WVT: 13.2.1.1In inch-pound units as follows:WVT 5G /t ! /A 5grains per ft 2per 1h (1 where:G 5weight change, grains (fromthe straight line, t 5time during which G occurred, h, andA 5test area, ft 2,1g 515.43grains.13.2.1.2In metric units as follows:WVT 5G /t ! /A 5grams per m 2per 24h(2where:G 5weight change, g (fromthe straight line, t 5time during which G occurred, h, and A 5test area, m 2. 13.2.2Calculate the permeance, WVP:13.2.2.1In inch-pound units as follows:WVP 5WVT /D p (35grains per ft 2per 1h per in. of mercury perms ! where:D p 5S (R 1- R 2, S 5in. Hg (saturationvapor pressure at test temperat ure, (seeTable 1, R 15relative humidity at vapor source, and R 25relative humidity at vapor sink. 13.2.2.2In metric units as follows:WVP 5WVT /D p (45grams per m 2per 24h per millimetreof mercury, -metric perms ! where:D p 5S (R 1- R 2, S 5 mm Hg (saturationvapor pressure at test temperature, (seeTable 1, R 15relative humidity at vapor source, and R 25relative humidity at vapor sink. 14. Report 14.1Report the following information:14.1.1Method of coating application and curing procedure used. 14.1.2Mean film thickness of the test specimens for each material. 14.1.3Type of film support used, if any. 14.1.4Method used (TestMethod A (DryCup or Test Method B (WetCup. 14.1.5Test temperature and relative humidity in the test chamber. 14.1.6Computed rate of water vapor transmission (WVT,either in inch-pound or in metric units. 14.1.7The computed permeance in terms of both perms and metric units. 15. Precision and Bias 715.1In an interlaboratory study of these test methods in which one operator in each of three laboratories determined in triplicate the permeance of three coatings covering the range of interest for vapor barriercoatings, the interlaboratory standard deviation for the dry-cup procedure was found to be 0.073perms with 6df and the interlaboratory wet-cup coefficient ofvariation 21.54%relative with 6df, with no results havingbeen discarded. Based upon these values, the following criteriashould be used for judging, at the 95%confidence level, theacceptability of results:15.1.1Repeatability :15.1.1.1Test Method A Two results, each the mean oftriplicate runs, obtained by the same operator should beconsidered suspect if they differ by more than 0.25perms atdry-cup permeance of less than 1.0perms.15.1.1.2Test Method B Two results, each the mean oftriplicate runs, obtained by the same operator should beconsidered suspect if they differ by more than 74.2%relativeat wet-cup permeances of 5to 30perms.15.1.2Reproducibility Intralaboratory precision is normally better than interlaboratory precision. However, oneparticipant in this exchange has noted relatively large differences when the same coating was tested in quadruplicate withfairly long intervals between tests.15.2Bias is not applicable to these test methods.16. Keywords16.1permeability; permeance; perms; water vapor permeance; water vapor transmission The American Society for Testing and Materials takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years and if not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standards and should be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards, at the address shown below.7Supporting data are available from ASTM Headquarters. RequestRR:D1- 1064. TABLE 1Saturation Vapor PressureTemperaturePressure FCin. Hg mm Hg 72.322.40.80020.31672.522.50.80520.44072.722.60.81020.56572.922.70.81620.69073.122.80.81920.81573.322.90.82420.94173.423.00.82921.06873.623.10.83421.19673.823.20.84021.32474.023.30.84521.45374.223.40.85021.58374.423.50.85521.71474.523.60.86021.84599.337.41.89448.10299.537.51.90448.36499.737.61.91448.62799.937.71.92548.891100.137.81.93549.157100.237.91.94649.424100.438.01.95649.692100.638.11.96749.961100.838.21.97850.231101.038.31.98850.502101.138.41.99950.774101.338.52.01051.048101.538.62.02151.323This standard is copyrighted by ASTM, 100Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 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