Possible causes and corresponding solutions for the problem of
sealant drumming:
a) Low environmental humidity
Low environmental humidity causes slow curing of the sealant. For example, in spring and autumn in northern my country, the relative humidity of the air is low, sometimes even lingering around 30% RH for a long time.
Solution: Try to choose seasonal construction for temperature and humidity issues.
b) Large environmental temperature difference (excessive temperature difference on the same day or two adjacent days)
During the construction process, the construction unit hopes that the curing speed of the sealant should be as fast as possible, so as to minimize the possibility of being affected by external factors. However, there is a process for sealant curing, which usually takes several days. Therefore, in order to accelerate the curing speed of the glue, the construction personnel usually carry out the construction under suitable construction conditions. Usually, the weather (mainly temperature and humidity) is selected for construction at a temperature that is stable and suitable for construction (maintained at a certain temperature and humidity for a longer period of time).
Solution: Try to choose a season and time period with a small temperature difference for construction, such as cloudy construction. In addition, the curing time of the silicone weather-resistant sealant needs to be short, which can also ensure that the sealant will not be displaced by other external forces during the curing process to cause the glue to bulge.
c) Panel material, size and shape
The substrates bonded by sealants are usually glass and aluminum. These substrates will expand and contract with temperature as the temperature changes, which will cause the glue to be subjected to cold stretching and hot pressing.
The coefficient of linear expansion is also called the coefficient of linear expansion. When the temperature of a solid substance changes by 1 degree Celsius, the ratio of the change of its length to its length at the original temperature (not necessarily 0°C) is called the “coefficient of linear expansion”. The unit is 1/℃, and the symbol is αt. Its definition is αt=(Lt-L0)/L0∆t, that is, Lt=L0 (1+αt∆t), where L0 is the initial size of the material, Lt is the size of the material at t ℃, and ∆t is the temperature Difference. As shown in the above table, the larger the size of the aluminum plate, the more obvious the bulging phenomenon of the glue in the glue joint. The joint deformation of the special-shaped aluminum plate is larger than that of the flat aluminum plate.
Solution: Choose aluminum plate and glass with a small linear expansion coefficient, and pay special attention to the long direction (short side) of the aluminum sheet. Effective heat conduction or protection of the aluminum plate, such as covering the aluminum plate with a sunshade film. The “secondary sizing” scheme can also be used for construction.
d) Influence of external forces
High-rise buildings are susceptible to the influence of the monsoon. If the wind is strong, it will cause the weathering glue to bulge. Most cities in our country are in the monsoon zone, and the curtain wall buildings will sway slightly due to external wind pressure, resulting in changes in the width of the joints. If the glue is applied when the wind is strong, the sealant will bulge due to the displacement of the plate before it is completely cured.
Solution: Before applying glue, the position of the aluminum sheet should be fixed as much as possible. At the same time, some methods can also be used to weaken the effect of external force on the aluminum sheet. It is forbidden to apply glue under the condition of excessive wind.
e) improper construction
1. The glue joint and base material have high humidity and rain;
2. The foam stick is accidentally scratched during construction/the surface depth of the foam stick is different;
3. The foam strip/double-sided tape was not flattened before sizing, and it bulged slightly after sizing. It showed bubbling phenomenon after sizing.
4. The foam stick is incorrectly selected, and the foam cannot be low-density foam sticks, which must comply with the relevant specifications;
5. The thickness of the sizing is not enough, too thin, or the thickness of the sizing is uneven;
6. After the splicing substrate is applied, the glue is not solidified and moved completely, causing displacement between the substrates and forming blisters.
7. Alcohol-based glue will bulge when applied under the sun (when the substrate surface temperature is high).
Solution: Before construction, make sure that all kinds of substrates are in the construction conditions of weather-resistant sealant matters, and the temperature and humidity in the environment are also in the appropriate range (recommended construction conditions).
Post time: Dec-15-2021