Signification et objectif
5.1 One of the factors affecting the performance provided by organic coatings is its ability to resist or help water vapor pass through. In some services, such as exterior wood and masonry, the coating needs to allow the right amount of water vapor to pass through the film without damaging it. Donc, the water vapor transmission characteristics of coatings are very important to evaluate their practical performance.

5.2 The purpose of these test methods is to obtain the value of water vapor transfer through the coating, which ranges from high to low permeability. These values are used for design, manufacturing, and marketing.

5.3 Water vapor transmittance is not a linear function of film thickness, température, or relative humidity.

5.4 The values of water vapor transmittance (WVT) and water vapor permeability (WVP) can be used for the relative rating of the coating only if the coating is tested under the same tightly controlled temperature and relative humidity conditions and the thickness is equal.

5.5 Méthode d'essai A – The Cheers method is a selective test method to obtain values associated with conventional dwellings that are not expected to have high relative humidity.

5.6 Méthode d'essai B – Wet cup method is the test method of choice to obtain values associated with applications with high expected relative humidity near the barrier material. En général, the more permeable the coating is to water passage, which is typical of many water-reduced coatings, the greater the affinity for water and the greater the transmittance when tested and exposed to high humidity conditions. Water absorption may reduce the density of the coating compared to a dry environment, thus allowing moisture to easily diffuse and leading to a higher water vapor transmittance (WVTR).

ASTM D1653-2021: Méthode d'essai pour la perméabilité à la vapeur d'eau des revêtements organiques

Champ d'application
1.1 These test methods cover the determination of the rate at which water vapor passes through paint, vernis, varnish and other organic-coated films. Films can be free films or applied to porous substrates.

1.2 A similar but more generally applicable test method is test method E96, which should be considered when other materials are involved.

1.3 Test Methods Two test methods are introduced in D1653, comme suit:

1.3.1 Méthode d'essai A – Cheers method, et

1.3.2 Méthode d'essai B – Mouillé (Penn) cup method.

1.3.3 Consistency should not be expected between the results obtained by different methods or test conditions. A method closer to the conditions of use should be chosen.

1.4 Les valeurs exprimées en pouces-livres doivent être considérées comme des valeurs standard.. Les valeurs données entre parenthèses sont des transformations mathématiques des unités SI et sont uniquement à titre de référence et ne sont pas considérées comme standard.. The conversion coefficients are shown in 13.2.1.2 et 13.2.2.2.

1.5 There are instruments on the market that claim to measure the water vapor transport of thin films more easily and rapidly than those described in test methods D1653 and E96. They run essentially the same type of test as the ASTM method, but in an instrumental manner. Cependant, there does not appear to have been a side-by-side test to compare the measurements of such instruments with the precision and accuracy of these ASTM methods.

ASTM D1653-2021: Méthode d'essai pour la perméabilité à la vapeur d'eau des revêtements organiques

1.6 This standard is not intended to address the safety issues, si seulement, associé à son utilisation. Il est de la responsabilité de l'utilisateur de cette norme d'établir des mesures de sécurité appropriées., pratiques sanitaires et environnementales et pour déterminer l’applicabilité des restrictions réglementaires avant utilisation.

1.7 La présente Norme internationale a été élaborée conformément aux principes de normalisation internationalement reconnus établis dans la Décision sur les principes pour l'élaboration de normes internationales., Lignes directrices et recommandations émises par le Comité des obstacles techniques au commerce de l'Organisation mondiale du commerce.