December 21, 2023
Winter is approaching, with the gradual increase of cold air activities; the temperature across the country has begun to drop. According to the latest weather forecast, in the next few days, the eastern part of the northwest, northeast, North China, Huanghuai, Jianghan and other places will drop 4 to 6 degrees, and the maximum temperature drop in the central and eastern Inner Mongolia will reach 8 ~ 10 degrees. And the first snow has fallen in Changchun and other places, covering the city with a new coat. The colder the winter, the more safety and quality of the building is needed to shelter the people. Today, let's master the use of silicone structure sealant, a building structure adhesive sealing material, and guard the building safety!
The ambient temperature is very low in winter, the following problems may occur:
1) When the temperature is too low, the wettability of silicone structure sealant and the substrate surface is reduced, and there may be imperceptible fog or frost on the substrate surface, which affects the bonding between silicone structure sealant and the substrate.
2) Under low temperature and low humidity conditions, the curing speed and bonding speed of silicone structure sealant are slower than normal, which will lead to longer curing time and affect the construction.
Winter construction problems：
There are two kinds of architectural silicone structure sealant used in the construction of curtain wall engineering according to the composition classification: one is one-component silicone structure sealant, and the other is two-component silicone structure sealant. The curing mechanism and factors affecting the curing of the two types of silicone structure sealant are shown in the table below.
Winter construction countermeasure
In accordance with JGJ 102-2013 "Technical Specification for Glass Curtain Wall Engineering" section 9.1 regarding general processing, the injection conditions for silicone structural sealants must align with the specifications of the product. For instance, BAIYUN brand silicone structural sealant requires an environmental range of 10°C to 40°C with a relative humidity of 40% to 80% in a clean setting, and construction is not recommended during rain or snow. It's important to note that different manufacturers may have varying environmental requirements.
During winter construction, it is advisable to implement heating measures to ensure the construction temperature remains above 10°C. If there are specific circumstances requiring construction in lower temperatures (slightly below 10°C), conducting a small-scale adhesive test before use is recommended. Perform peel adhesion tests to confirm proper curing and bonding, and, if necessary, consider extending the curing time. When needed, the use of xylene for cleaning and applying primer coatings can be considered to expedite bonding and mitigate the risk of poor adhesion due to low environmental temperatures.
1) Before construction, conduct adhesive tests in advance and strictly follow the recommended methods from the adhesive tests.
▲ Comparison of poor (left) and good (right) adhesion in aluminum bonding for a certain project.
2) The materials used during construction (aluminum, glass, sealant, cleaning agents, primer, etc.) come from various batches. Be aware that differences may exist between batches, and it's essential to conduct on-site adhesive tests randomly for each batch entering the site during the production process.
▲ Comparison of poor (left) and good (right) adhesion in on-site adhesive tests.
3) During construction, cleaning or primer application methods should align with the construction process. Strictly follow the "secondary cloth method" for cleaning, apply the primer promptly after solvent evaporation, ensuring a thin and even coat. Pay attention to the transition to the next step, and it's advisable to perform adhesive construction within half an hour after applying the primer.
▲ Uneven primer application causing localized non-adherence in a particular case.
▲ Uneven primer application causing non-adherence in sheet-like patterns in a specific case.
4) During the injection process, ensure the thorough mixing of components A and B within the manufacturer's recommended mixing ratio range. Confirm through butterfly tests and tensile tests. When changing containers, ensure proper ventilation. Inadequate ventilation may result in "bubble glue" – silicone structural sealant with numerous dense bubbles. Bubble glue has poor adhesion to substrates (aluminum, glass, etc.), leading to separation when pulled by hand, leaving black marks on the substrate.
▲ Poor adhesion to glass due to bubble glue in a specific case.
▲ Poor adhesion to aluminum due to bubble glue in a specific case.
5) After completing the on-site panel fabrication, move the panels horizontally to the curing area for proper curing. During the moving process, avoid misalignment between the aluminum frame and glass, as it can impact the bonding quality of silicone structural sealant.
Maintenance environment and maintenance time should ensure that the unit rubber cutting qualified.
After the completion of silicone structural sealant injection, the curing process should take place in a clean and well-ventilated environment with temperatures maintained between 10-40°C and humidity between 50-90%. When curing in a low-temperature and low-humidity environment, it may be necessary to extend the curing time appropriately. This is particularly evident in single-component silicone structural sealants, where the curing process is notably influenced by the duration of curing. In the same environment, a longer curing time results in a higher degree of solidification.
▲ Under low-temperature curing conditions, the curing time for a 10mm deep injection of single-component structural sealant increases from 10 days to 15 days, with an extended curing time.
If necessary, measures can be taken to raise the ambient temperature and humidity. The final determination of the curing time for finished units should rely on the tape cutting test, ensuring that the components are fully cured. Only after passing the tape cutting test (as shown in the image) can installation and handling proceed.
