The water vapor of the exterior wall coating of the building is compared by the performance test method

1 Foreword
Exterior paint long-term exposure to the natural environment, in addition to the requirements of good decoration, water resistance and weather resistance, as part of the external wall insulation system, but also should assume the important responsibility of building energy conservation. Water is the primary culprit in destroying the insulation effect of the building's exterior walls. In the construction structure, water in the form of solid water, liquid water, gaseous water through diffusion, leakage, ice and other phenomena to migrate, of which people are more concerned about liquid water leakage caused by the failure of the external wall insulation, I do not know the external wall paint water vapor penetration performance also affects the effectiveness of the external wall insulation system
China
.2 Exterior wall coating water vapor through the performance overview
Due to the building exterior wall insulation system inside and outside the temperature difference, the temperature of the higher side of the water vapor moisture pressure is greater, in the water vapor pressure difference, water vapor molecules from the high-pressure side through the outer wall paint to the low-pressure side migration penetration, this process is called water vapor penetration. In cold areas or winter, the inside temperature of the building's exterior wall is generally higher than the outside, water vapor from the building's inner layer to the outside migration, if the external wall paint moisture performance is poor, hindering the water vapor outward discharge, not only affect the appearance of color, but also will produce stress, so that the paint bubble, fall off, at the same time because the water vapor is rich in the wall, easy to lead to the wall internal condensation, so as to the wall heat, structure and other adverse effects.
JG/T 149-2003 "Expansion polyphenyl sheet thin dust external wall external insulation system" clearly stipulates that the water vapor moisture flow density of thin dust outer wall insulation system should not be less than 0.85g/(m2.h), according to the outer wall insulation system water vapor moisture flow density from the inside material to the outside material increase, Therefore, the moisture flow density of water vapor in the exterior wall coating is much higher than 0.85g/(m2.h) in order to ensure the normal breathability of the entire exterior wall insulation system. The reference to "water vapor moisture flow density" in this standard refers to the quality of gas phase water flowing through the unit area in a unit of time, and "permeability" and "water vapor transmission rate" are the same terms to describe the performance of water vapor through, but in different standards, the calculation methods of these three indicators are somewhat different.
3 Introduction and comparison of the test method of water vapor through performance of exterior paint
With the development of science and technology, most exterior paints on the market already have a certain water vapor through performance, but whether to meet the use of standards still need further testing and verification. At present, there are two main standards for the performance test method of water vapor in exterior coatings: GB/T 17146-1997 "Building materials water vapor through performance test method" and JG/T309-2011 "The determination and grading of water vapor through exterior paint". The two standards will be compared below from the four aspects of application scope, test principle, test instruments and materials, and sample preparation.
3.1 Scope of application
GB/T 17146 is the national standard, which stipulates the wet flow density and moisture permeable test method of various building materials for flaky, plate-shaped insulation, waterproof moisture, decoration and other uses. JG/T 309 is the industry standard of the construction industry, which specifies the water vapor pass rate measurement method of the outer wall coating used on brick, stone, concrete and other porous substrates of industrial and civil buildings. Usually the industry standard belongs to the professional and technical standard, is the complement to the national standard. For exterior coatings that meet the scope of application of the above two standards, water vapor can be tested for performance according to one of them.
3.2 Test principle
The test principle of JG/T 309 is to add a quantitative ammonium dihydrohydrogen phosphate saturation solution to the test cup, which rapidly increases the relative humidity of the air above the test cup to 93%. The test cup is closed using a membrane-like sample to be tested or by applying a substrate of the porous structure of the sample to be tested. Place the
cup in a controlled space with controlled temperature and relative humidity, so that the water vapor concentration is poor on both sides of the sample. Weighing the test cup at an appropriate time interval, when the mass change is in directly related to the change of the time interval, the water vapor pass rate can be measured by the change of mass. Since this method is calculated by reducing the quality of the test cup, it can also be called the "weight reduction method" test method. In contrast, GB/T 17146 offers two different methods: desiccant and water. Water method, i.e. weight loss method, while desiccant method, sample encapsulation with water method, but the test disk (i.e., JG/T 309 "test cup") into the desiccant, the internal relative humidity can be considered 0. Place the test plate in a space controlled by temperature and humidity timed weighing, due to the presence of humidity difference on both sides of the sample, the weight of the test disk will continue to increase, by measuring the weight of the increased test disk to measure the water vapor pass rate, the method is also known as "weight gain method." Theoretically, both test methods can obtain the correct test data. However, in the course of the actual weight gain test, the drying ability of the desiccant is decreasing, and the humidity difference on both sides of the sample changes, which can easily cause errors in the test data. In the weight reduction method, the test cup is loaded with a solution or distilled water to keep the inside at a high humidity level, while the outside of the test cup can be stabilized in a low humidity environment using a constant temperature and humidity instrument, which can achieve automatic control of the constant humidity difference, which is good for the accuracy of the test. Therefore, the test differences in the weight reduction method in the two standards are mainly compared below.
3.3 Test instruments and materials
3.3. 1 Test containers and sealing methods
JG/T 309 requires test cups made of corrosion-resistant, certain strength materials such as glass, polyethylene, aluminum, etc., with a diameter of 81mm and a test area of at least 50cm2. Samples and cups are effectively sealed with a mechanical clamping device or screw fitting with a ring cover, in conjunction with a suitable sealing ring (see Figure 1), or molten wax can be used as a sealant. Compared with the normative test container provided by JG/T 309, GB/T17146 puts forward the basic requirements of the test vessel, and on this basis, a variety of test plate designs are listed according to the thickness and permeability of the test. The test plate should choose a large and shallow plate, the plate caliber is at least 60mm, the thicker the sample, the larger the plate caliber. For thicker and larger samples, aluminum foil or metal material should be used to mask the part of the sample that is out of the plate, so that the plate area is basically equivalent to the test area, to prevent water vapor from the edge and should not be exposed parts of the escape/escape. For samples prone to contraction or warping, a railing with flanges should be set outside the plate, the inside is coated with sealant, the sample is fixed in the center position inside the test disc ring, and finally with aluminum foil around the flange and the bottom of the rail ring, complete the seal, see Figure 2. In addition to sealing with sealants, GB/T17146 also allows gasket seals.
3.3.2 Relative humidity inside and outside the
The JG/T 309 test cup contains a saturated solution of 1665g ammonium dihydrohydrogen phosphate and 4500g water, which can achieve a relative humidity of 93% of the air above the test cup, while the test cup should be in a room or box with a temperature (23 s2), relative humidity (50 s 5) degrees C, and a wind speed of less than 0.3m/s. GB/T17146 Water method test, the sample plate is placed distilled water, the air humidity above the test disk is considered to be 100%, the surrounding environment can be selected between 21 degrees C to 23 degrees C, the relative humidity is generally maintained at (50 degrees 2).
3.4 sample preparation
JG/T 309 is an industry standard for exterior coatings, and therefore for different coating types, such as thin-coated water-based coatings, solvent-based coatings, elastic building coatings and thick slurry coatings (inelastic), detailing the type of substrate to be used, coating volume, preparation methods and maintenance time, see Table 1. GB/T 17146 focuses more on the macro-presentation of samples, such as thickness uniformity, sample representation, sampling thickness, etc.
preparation of test samples
4 to latex paint as an example to detail the JG/T 309 water vapor pass rate test method

4.1 Test instrument
Jinan Languang Electrical and Mechanical Technology Co., Ltd. produces W3/031 water vapor pass rate tester.
4.2 Test Principle
Weight Reduction Test, at a certain temperature, so that the two sides of the sample form a specific humidity difference, water vapor through the test cup sealed in the test cup mouth sample into the dry side, by measuring the weight of the test cup over time changes, calculate the test sample water vapor pass rate and other parameters.
4.3 Sample preparation
4.3.1 substrate
latex paint is a water-based coating, which is made of a non-self-supporting coating and requires the use of a porous substrate as required by Table 1. JG/T309 stipulates that the water vapor pass rate of the porous substrate should be greater than 240g/(m2.d), so the porous nonwoven substrate was selected for this test, as shown in Figure 3. It has been tested and verified that its water vapor pass rate is 435.21g/(m2.d), which meets the requirements of the standard.
preparation of nonwoven substrates
4.3.2 samples
latex paint is diluted according to the product instructions and evenly coated on nonwoven substrates. According to the requirements of JG/T309, "coating dry film thickness≥80 m, brush coating, at least 2 channels, 6h per channel interval", the sample coating thickness after coating is 147.6 m, the average weight of 309.62g/m2. After coating, the maintenance 14d, the maintenance environment temperature and humidity are (23±2) degrees C, (50±5).
4.3.2 Sample condition adjustment
after maintenance, the sample will be under the following conditions for three cycle aging tests: at (23±2) degrees C, immersed in GB/T6682-2008 three-stage water 24h, immersion coating should be down and ensure complete immersion. The sample is then dried at (50±2) at a temperature of 24h. After the aging test, store the sample at 48h under standard maintenance conditions prior to testing. If the coating appears to drum, cracking phenomenon, should be re-sampled.
4.4 Test
cut the sample to 3 samples with a diameter of 74 mm and sealed them in a face-up coating in a test cup containing (200±5) g of ammonium dihydrohydrogen saturated solution, and placed 3 test cups on the test chamber of the instrument. Because the instrument is using automatic control intermittent weighing measurement, set a certain weighing interval, test temperature of 23 degrees C, test humidity 55% can start the test. When water vapor penetration reaches equilibrium, the test automatically stops, and the results are automatically stored and the data curve is displayed on the accompanying computer screen.
4.5 Results Calculated
4.5.1 Water vapor pass rate of the coating-coated porous substrate
according to the calculation method vi of the water vapor pass rate vi for the coating-coated porous substrate in JG/T309 (1):
water vapor The calculation method of pass-through rate Vi
: Vi-tested water vapor-through rate of g/(m2.d); m1, m2-total mass (mg) of time t1 and t2, respectively; t1, t2-time (h); Ai-test surface area (cm2).
the water vapor pass rate measured in 3 samples was 76.54g/m2.d, 77.21g/(m2.d), and 76.93g/(m2.d).
4.5.2 Water vapor pass rate of coating
According to the calculation method of non-self-supporting coating water vapor pass rate V on porous substrate in JG/T309 (2):
water vapor pass rate Vi calculation method
: V-coated water vapor pass rate g/(m2.d); Vcs-coated porous substrate water vapor pass rate g/(m2.d)) and Vs-porous substrate water vapor pass rate g/(m2.d).
can be obtained that the water vapor pass rate of the three samples of the coating is 92.87g/(m2.d), 93.86g/m2.d, 93.45g/(m2.d), and the average water vapor pass rate of the coating is 93.39g/(m2.d). 5 Summary
VS GB/T17146-1997 "Building Materials Water Vapor Through Performance Test Method" and JG/T 309-2011 "External Wall Coating Water Vapor Pass rate" As to the similarities and differences of the test method, the test method of water vapor pass rate in JG/T 309 is introduced in detail in JG/T 309, which proves that the water vapor pass rate test of weight reduction coating has certain rationality and operability.