Water vapor permeability test method GB17146 for building materials

GB17146-1997 Water vapor permeability test method for building materials: This standard specifies the method of testing the wet flow density, moisture permeability and moisture permeability coefficient of various building materials
.
This standard applies to sheets.
Various building materials
such as heat insulation, waterproof moisture insulation, and decoration of these shapes can be obtained in the form of plates or by processing.
This standard also applies to the determination
of water vapor permeability of other sheet or plate materials.
Detection principle: 1, there are two basic test methods - a desiccant method and a water method
.
These tests are designed to reliably measure the amount of water vapor transmitted through permeable and semi-permeable materials in a simple way and to represent them
appropriately.
These values can be used for design, manufacturing, and sales
.
2, desiccant method - a specimen is encapsulated in the opening of the test plate with desiccant, assembled into a controlled ambient atmosphere, weighed regularly to determine the speed at
which water vapor enters the desiccant through the sample.
The water method is the same as the desiccant method, but the distilled water is held in the disc and weighed regularly to determine the speed at which the water evaporates through the specimen into the ambient
atmosphere.
The results obtained through tests under different test methods and conditions will be inconsistent, so the conditions close to the conditions used should be selected as closely as possible for testing
.
Test Instruments: WVTR-RC6 Water Vapor Transmittance Tester (Weight Gain and Loss One) Device Specimen Plate: The specimen plate should be made of materials that are not easy to corrode, and can not pass through water or water vapor, the shape of the disc is arbitrary, but the weight should be light, and a large and shallow plate
should be selected.
The diameter of the disc should be as large as possible, at least 60 mm in diameter, the thicker the specimen, the larger the pan port should be, and the diameter of the disc should be greater than 4 times
the thickness of the specimen.
The paving area of desiccant or water should not be less than the area of
the pan mouth.
When using a rack of the kind described in 8.
3.
1, the area affected by the rack shall not exceed 10%
of the pankou area.
When the specimen will shrink or warp, a loop
with a flange should be placed outside the pan mouth.
When the specimen area is larger than the pan port area, the portion of the specimen beyond the pan port is an error source (especially for thick specimens) and should be obscured with a mask as described in 8.
1 so that the pan port area is similar to or equivalent to the test area
。 The excess will cause water vapor to pass through and the result will be too large.
This type of error should be limited to about 10% to 12%, so for thick specimens, when using a sample disc with a diameter of 254 mm or greater (square or round), the width of the ring should not exceed 19 mm, the width of the 127 mmpan mouth (square or round) should not exceed 3 mm, the width of the 76 mmpan mouth (square or round) should not exceed 2.
8 mm, and the flange height of the ring should not exceed 6 mm
on the upper surface of the specimen.
The disc depth of the desiccant method and the water method can be different, but a depth of 19 mm (below the pan mouth) satisfies
both methods.
Desiccant and water: For the desiccant method, a particle size of 2.
5 mm to 0 should be placed in the specimen plate.
Small granules between 63 mm anhydrous calcium chloride, which should be dried
at 200 °C before use.
If calcium chloride and the sample will have a chemical reaction, silica gel adsorption desiccant can be used, but the hygroscopic weight gain at the time of the test must be limited to less than
4%.
For the water method, distilled water
should be placed in the specimen plate.
Before preparing the specimen, the water temperature should be controlled within 1 °C of the test temperature to prevent condensation
on the inner surface of the specimen when placed in the work room.
Sealant: In order to encapsulate the specimen to the disk, the sealant must have a high blocking effect on the passage of water vapor (and water), and during the required test time period, the sealant must have no significant weight loss or weight gain, that is, the amount of weight loss to or from the environment shall not be greater than 2% ‰, and must not affect the vapor pressure
in the filling pan.
For moisture permeability below 2.
3× 10-7 g/(m's · Pa) is to use molten asphalt or wax
.
8.
1.
The specimen is encapsulated to the test plate and the specimen is sealed or clamped to the specimen plate, the disc determines the area where the specimen is exposed to water vapor in the dish, if necessary, the top surface of the specimen exposed to the air is obscured, so that the shape and size of the pan can be copied, and the edge of the specimen and any other parts that should not be exposed should be completely sealed, to prevent water vapor from entering or escaping from these places, and the same is necessary to ensure that the specimen only exposes the demarcated area
.
Appendix A (Appendix to the Standard) describes the encapsulation method
.
Note
.
The water vapor transmittance of some materials (especially wood) will be closely related to the relative humidity of the environment before the test, and if the previous relative humidity is higher than the test conditions, the water vapor transmittance result may be abnormally high; And vice versa
.
Therefore, samples such as wood and paper products should be placed in an atmosphere with a relative humidity of 50% of constant weight before the test, and the wet disc may be beneficial
to the test after pretreatment so that the wet disc is as small as possible.
Test steps of the desiccant method: 1.
Put the desiccant into the disc and leave a gap of about 6 mm between it and the lower surface of the specimen, so that the specimen plate can be swung to agitate the desiccant
during each weighing.
2.
Encapsulate the specimen on the disk (see 8.
1), put the specimen into the studio facing up, and immediately weigh and record
.
3.
Regularly weigh the quality of the recording disk assembly, 8 or 10 data points are sufficient
during the test.
The time of weighing should also be recorded, accurate to 1%
of that interval.
Such as hourly weighing, time recording accuracy of 30 s; As recorded per day, allowed to 15 min
.
The mass may become very fast at first, and the rate of change will later reach a steady state, and the specimen plate should not be removed from the control atmosphere when weighing, but if it is necessary, the specimen should be kept under different conditions < temperature or relative humidity or both) as short
as possible.
4 End the test before the water absorption exceeds a certain proportion of the initial mass of the
desiccant (10% for anhydrous calcium oxide and 4% for silica gel).
This limit may not be very strictly determined, when the moisture content of the specimen itself changes, the weight gain of the desiccant may be greater than or less than the weight gain of the specimen plate, and this situation can be considered for flexible treatment during experimentation
.
Test step 1 of the water method, with distilled water injected into the specimen plate to a height of 25 degrees from the specimen (25 Shi 5) mm high (there is an air gap between the water surface and the specimen is to make a small area of water vapor, reduce the risk of water contact with the specimen when operating the specimen plate, which is necessary, for some materials such as paper, wood or other hygroscopic materials, this contact will make the test invalid).

The depth of the water should not be less than 3 mm to ensure that the water can cover the bottom of the disc during the entire test, if it is a glass dish, as long as it can be seen that the water covers the bottom of the disc all the time, there is no need to specify the water depth
.
In order to reduce the rush of water, a mesh frame made of lightweight and corrosion-resistant material can be placed in the disc to separate the water surface, which should be at least 6 mm lower than the lower surface of the specimen, and the reduction of the water surface should not be greater than 10%.

2.
In order to facilitate water injection in the dish, it is recommended to punch a small hole in the wall of the specimen plate, and its position is above
the water level.
Dry the empty disc, seal the specimen to the pan mouth with sealant, fill the dish with water through the small holes, and then close
the small holes.
3.
Weigh the specimen disc assembly and place it horizontally in
the studio.
If the specimen cannot withstand the influence of condensate water on the surface, the temperature difference between the specimen disc assembly and the control gas ammonia should not exceed 3 °C to prevent the specimen from being affected by the condensate water
.
4.
When conducting the test of the inverted water method, in addition to placing the plate upside down
.
The plate must be placed horizontally so that water can evenly cover the inner surface of the specimen, although the specimen is still somewhat deformed
due to the weight of the water.
For specimens with high moisture permeability, the placement of the specimen disc must ensure that the circulating air can pass through its exposed surface
at a specified speed.
The specimen tray can be placed face up to the balance during weighing, but the wet surface of the specimen will not be covered by water, in which case the weighing time must be as short
as possible.