With the arrival of winter, the weather is getting colder and colder, the temperature in the north is -20 ℃ ~ -10 ℃, and the temperature in the south is -10 ℃ ~ 0 ℃. At the beginning of December, it was snowing early in the south where it was rare to see snow. As we all know, silicone sealant is a kind of room temperature curing adhesive, which is greatly affected by the environment (temperature, humidity), so what problems will be encountered in the construction of silicone sealant in low temperature environment in winter? How can I resolve or avoid these problems?

1. Classification and function of silicone sealant for construction

Generally, three types of silicone sealants are used in curtain wall construction: structural adhesive, weatherproof adhesive, and hollow structural adhesive (as shown in the figure below). Structural glue is mainly used for bonding between profiles and glass, and plays a structural role. Weather-resistant adhesive is mainly used for waterproof sealing of joints of exterior walls such as glass and aluminum plates. Insulating glass silicone structural sealant is mainly used for the secondary sealing of insulating glass, which plays the role of structural bonding and sealing to glass plates. Silicone sealant is a small material in the building, but it plays a very important role. Therefore, every glue used in the building curtain wall must be streamlined and standardized.

2. What are the common problems of silicone sealants in low temperature environment in winter?

1) Slow curing

The primary problem with silicone sealants at low temperatures is slower cure. The curing process of silicone sealant is a chemical reaction process, and the temperature and humidity of the environment have a certain effect on its curing speed. Generally, for one-component silicone sealants, the higher the temperature and humidity, the faster the curing speed. In the autumn and winter season, the temperature drops sharply, which reduces the curing reaction rate of the silicone sealant, resulting in slower surface drying time and deeper curing. Generally, when the temperature is lower than 15 ° C, the curing speed becomes slower.

For metal sheet curtain wall, because the sealant solidifies slowly in autumn and winter seasons, when the temperature difference between day and night is large, the gap between the plates will be greatly stretched and compressed, and the sealant at the joints is prone to bulging.

2) Deviation of bonding effect

As the temperature and humidity decrease, the adhesion of the silicone sealant to the substrate will also be affected. Generally suitable for the environment of silicone sealant: two components should be used in clean environmental conditions of 10 ℃ ~ 40 ℃, relative humidity of 40% ~ 60%; single component should be 4 ℃ ~ 50 ℃, relative humidity of 40% Use under ~ 60% clean environmental conditions. When the temperature is low, the curing rate and reactivity of the sealant are reduced, and the wettability of the surface of the adhesive and the substrate is reduced, resulting in a longer period of time for the adhesive to form a good adhesion to the substrate.

When the temperature is too low, condensation water or frost is easily formed on the surface of the substrate during the volatilization of the cleaning solvent, which affects the adhesive effect of the silicone sealant.

3) Colloid thickening

As the temperature decreases, the silicone sealant will gradually thicken and the extrudability will be poor. For two-component sealant, thickening of component A will cause the pressure of the glue machine to increase, and the amount of glue will be reduced, which will cause the glue to be full. For the one-component sealant, the colloid is thickened. During the process of manually using a glue gun, the extrusion pressure is relatively large, which reduces the efficiency of manual operation.

3. How to solve the above problems during winter sizing?

Use high-quality silicone sealant products and strictly follow the construction process guidelines. The recommended construction temperature of Sibao single-component silicone sealant: 4 ℃ ~ 50 ℃, the recommended construction temperature of Sibao two-component silicone sealant: 10 ℃ ~ 40 ℃, when the temperature is lower than the above temperature, construction is not recommended.

If the user must perform the construction below the above temperature due to the rush time of the curtain wall project, it is recommended to follow the steps below:

1) Pull off test. Before using the two-component sealant, pull-off test is required to determine the appropriate mixing ratio; single-component sealant needs to be tested for surface drying time to determine the operating time of the sealant at low temperature;

2) Peel adhesion test. Peel adhesion test should be performed in low temperature environment to confirm that the sealant can be cured and adhered well before use;

3) Clean the substrate. The cleaning process should use a suitable cleaning solvent and use the "two wipes" method to clean the substrate. After cleaning the substrate with a cleaning solvent, wipe it with a clean cotton cloth to ensure that the surface of the substrate is clean and prevent the residual solvent on the surface of the substrate from affecting the adhesion of the sealant to the substrate. After cleaning the substrate, the sizing must be completed within 1 hour, otherwise it must be cleaned again.

4) Apply primer (if necessary). First, a suitable primer should be selected. On the one hand, the primer chemically reacts with the substrate, and on the other hand, it chemically reacts with the silicone sealant, which acts as a bridge to promote the adhesion of the silicone sealant to the substrate. Use a natural hard brush or a clean lint-free cotton cloth to apply a thin and even primer on the surface of the interface to be glued (avoid repeated brushing). Do not pour directly or use the primer too much. After the primer is completely dry, apply the sealant. After the substrate is primed, apply the sealant within 1 hour. When the construction site is dusty, the sealant should be applied immediately after the primer is dried.

5) Extend the curing period. Due to the silicone sealant applied at low temperature, the overall curing rate and adhesion to the substrate are relatively slow, so it is necessary to appropriately extend the curing period in winter; during the curing period, avoid handling and movement before the sealant is cured.

6) Check. Under the conditions of low temperature construction, during the large-scale application of glue, the frequency of on-site tapping inspection of the silicone sealant must be increased, and quality control records must be made to ensure the construction quality.

7) It is recommended to carry out the following methods for the phenomenon of large temperature difference between day and night in autumn and winter: (1) It is recommended to work in a cloudy environment, because the temperature difference between day and night on a cloudy day is small, the deformation of the glue joint is small, and it is not easy to occur; Adopt appropriate sunshading measures to prevent the panel from being directly exposed to sunlight, reduce the temperature of the panel, and reduce the joint changes caused by temperature difference; (3) use the second application method, first apply 1/2 of the joint depth After the surface is dry, perform a second glue to fill the seams.