Test Methods for Water Vapour Transmission of Building Materials
1 Scope
This standard specifies the test methods for density of moisture flow rate, moisture permeance and moisture permeability of building materials.
This standard is applicable to all kinds of building materials which can be heat insulation, waterproof and moisture insulation, decoration and other purposes in sheet or plate shape or through processing.
This standard is also applicable to the determination of water vapour transmission (WVT) of other sheet or plate materials.
2 Normative References
The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated are valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below.
GB/T 4132-1996 Definitions of Terms Relating to Thermal Insulating Materials
3 Definitions
For the purpose of this standard, the definitions given in GB/T 4132 apply.
4 Principle
There are two basic test methods — desiccant method and water method. The purpose of these tests is to obtain, by means of simple apparatus, reliable values of water vapor transfer through permeable and semi-permeable materials, expressed in suitable units. These values are for use in design, manufacture, and marketing.
4.1 Desiccant method: the test specimen is sealed to the open mouth of a test dish containing a desiccant, and the assembly placed in a controlled atmosphere. Periodic weighings determine the rate of water vapor movement through the specimen into the desiccant.
4.2 Water method: the dish contains distilled water, and the weighings determine the rate of vapor movement through the specimen from the water to the controlled atmosphere.
4.3 A permeance value obtained under one set of test conditions may not indicate the value under a different set of conditions. For this reason, the test conditions should be selected that most closely approach the conditions of use. While any set of conditions may be used and those conditions reported, standard conditions that have been useful are shown in Annex C (informative).
5 Apparatus
5.1 Test dish
The test dish shall be of any noncorroding material, impermeable to water or water vapor. It may be of any shape. Light weight is desirable. A large, shallow dish is preferred. The diameter of dish should be as large as possible, the diameter of at least 60 mm, the thicker the sample, the larger the opening should be, the caliber of the dish should be greater than 4 times the thickness of specimen. The desiccant or water area shall be not less than the mouth area except if a grid is used, as provided in 8.3.1, its effective area shall not exceed 10% of the mouth area. An external flange or ledge around the mouth, to which the specimen may be attached, is useful when shrinking or warping occurs. When the specimen area is larger than the mouth area, this overlay upon the ledge is a source of error, particularly for thick specimens. This overlay material should be masked as described in 8.1 so that the mouth area is similar to or
Foreword II
1 Scope
2 Normative References
3 Definitions
4 Principle
5 Apparatus
6 Materials
7 Sampling and Preparation of Test Specimens
8 Procedure
9 Data Processing
10 Report
Annex A (Normative) Design and Sealing Method of Test Dish
Annex B (Normative) Saturated Vapour Pressure of Water at Different Temperatures
Annex C (Informative) Recommended Test Conditions
Annex D (Informative) Modification of Sealing Edge Influence of Specimen
Annex E (Informative) Conversion between SI and Imperial Units
