There are many reasons for the foaming of silicone weathering sealant during construction, and it is relatively complicated. It is difficult to use one method and one result to determine the cause of foaming. Silicone structural sealants generally complete the glue injection work in the factory. The environment and operating conditions in the factory are relatively good, and it is easy to meet the external conditions required when the silicone sealant is cured. Silicone weather-resistant sealants generally complete the injection work on the construction site, and the site environment and working conditions are poor. The external conditions required by the silicone weather-resistant adhesive during the curing process are not easily met. Climate, environment, operating conditions and other non-man-made factors have a great influence on the curing quality of silicone weathering adhesive. Therefore, the limitations of the environment and operating conditions in which the weathering glue is used determine the main cause of blistering. Let's make some analysis on these specific situations.

1. Air was wrapped in the glue during injection

Silicone weathering glue is generally completed on the construction site, and the working conditions are poor. Workers stand on the scaffold to inject glue, and the uniformity of the glue is not easy to grasp, and it is easy to entrap air in the glue joints. After sizing, the surface of the glue joint is scraped and pressed to make it smooth and smooth. The pads in the glue joint are generally closed-cell polyethylene foam rods. The air wrapped in the glue joints is not easy to overflow. Outside the bulge tension, the weather-resistant glue seam is generally wider and small in thickness. It provides high-displacement weather-resistant glue with low hardness, and the glue is very soft before curing. The bulge tension of the compressed air slowly propped up the glue seam to bubble up. This phenomenon is more likely to occur in the application of weather-resistant glue that can provide more than +25% of the glue seam displacement capacity. On the contrary, some weather-resistant adhesives with lower allowable displacement ability have higher hardness and thicker before curing. The bulge tension of the compressed air wrapped in the glue seam is not easy to support the glue to foam. Therefore, the more weather-resistant glue that can provide high displacement ability, the more attention should be paid to the uniformity of the glue when injecting the glue. Generally, vertical glue joint injection can be applied from bottom to top, which can overcome some blistering. More important is the proficiency and sense of responsibility of the work operator.

2. The interface is wet when injecting glue

When working outdoors, it often rains, especially in the summer in the south. It rains almost every day. If the inside of the interface is wet and dry after the rain, inject the glue directly, and wait for the sun to irradiate the substrate and glue joints. When the temperature rises, the moisture in the glue joint will evaporate, which will foam the uncured and soft glue, and sometimes the foam stick will also cause the glue to foam. Therefore, do not blindly seek progress during construction. Wait until the interface is dry before injecting glue to avoid the above situation.

3. Deflate the foam stick

The cushion rods in the glue seams are generally closed-cell high-foaming polyethylene foam rods. When placed, the internal airbags rupture and release air due to improper extrusion. When the glue is just injected, there will be bubbles or bulges. The bulging appearance, the solution to this situation, one is to cut the foam stick with the cut facing inward. The second is to use an open-cell foam stick or a foamed polyethylene foam stick to overcome the above situation. In another case, weather-resistant adhesives generally have more alcohol types. Alcohol-based weather-resistant adhesives will release ethanol when they are cured, and ethanol will react with some foam sticks. For example, when a construction site uses Yongan alcohol-based silicone weathering adhesive, it foams. However, when another oxime-type weather-resistant adhesive from Yongan Company was used for injection, there was no blistering. After encountering similar situations several times, the problem was solved by changing the foam stick or changing the glue.

4. Sun exposure when the glue is not cured

Silicone glue cannot be exposed to the sun before it is cured, especially if it is exposed to the sun just after the glue is injected, it will cause honeycomb bubbles inside the glue joint, which will cause the outside of the glue joint to bulge. This is the case in alcohol type silicon. It will be more obvious when ketone glue is used. In the hot summer construction, this situation is not easy to overcome. Avoiding sun exposure when injecting glue will overcome some bubbles. The specific method is to inject glue on the west or north side of the building in the morning, and on the east or south side of the building in the afternoon. After the glue is injected, the glue is cured for a period of time, and the surface layer has been skinned. When it is exposed to the sun, it has a certain resistance and can overcome some blistering.

5. The surface temperature of the substrate is too high

  When the silicone adhesive is cured, the temperature of the bonded material cannot exceed 50°C. This conclusion has been recognized by most silicone adhesive manufacturers. When the surface temperature of the substrate exceeds 50°C, the glue will cause foaming in the glue joints. The above-mentioned situation will be encountered in the weather-resistant caulking of the metal panel curtain wall. When the material to be bonded is exposed to the sun, especially the temperature of the aluminum sheet surface machine, the temperature will reach 80°C. At this time, the glue injection can easily cause the glue seam to bubble. Therefore, you should choose to inject glue in the second half of the afternoon or on a cloudy day to improve the above situation.

6. The temperature difference between day and night is large, and the thermal expansion and contraction of the interface are large

  This situation is more likely to occur when the aluminum curtain wall is injected with glue. Aluminum is a material with a large linear expansion coefficient, and the day and night temperature in spring or autumn in northern my country is relatively high. For example: when the sun shines directly on the aluminum plate at noon, the surface temperature of the aluminum plate can be as high as 60℃-70℃, and the temperature at night drops to about 10℃. The large aluminum plate expands and shrinks more due to heat, the interface displacement is large, and the weatherproof glue is caulked. Later, the actual displacement of the interface is borne by the glue joint. During the curing process, excessive and repeated expansion and contraction will cause the glue joint to bubble. Therefore, avoid the strongest direct sun at noon when the glue is injected to improve Some of the above blistering phenomena.

7. The climate in the north is dry in spring

  Silicone sealant must take advantage of the moisture in the air to form an elastic sealing material through polymerization. The temperature in the air is closely related to the curing speed. The spring climate in northern my country is dry, and the curing time is very long after the silicone rubber is injected. The uncured silicone sealant is easily affected by the external environment and provides opportunities for various blistering phenomena.