Hello everyone, in the first part of the last issue about the cause analysis and solution of the foaming problem during the use of sealants, we introduced three cases of foaming and their cause analysis and solutions, including random foaming, foaming from broken rods and blistering from chemical reactions. In this issue, we will continue to introduce the other three causes of blistering and their solutions, which are the blistering caused by the thermal expansion of the gas in the closed sealant joint, and the blistering caused by the moisture of the interface or accessory material. and blistering caused by construction under outdoor high temperature conditions

(4) Foaming caused by thermal expansion of gas in closed sealant joints

    This type of blistering occurs less frequently, and occasionally occurs in single components or doors and windows. This kind of foaming usually occurs in the sealant seam where the temperature of the sealant injection environment is relatively high and the sealant injection is relatively closed. Such blistering is not caused by the aforementioned breakage of the foam rod, and there is no problem with the foam rod, but after the sealant injection, there are local small blistering on the surface of a few sealant joints, or short strip-shaped blistering. As shown below

Figure 1 Blistering in closed sealant joints

    The reason for this type of foaming may be that in the entire closed sealant joint, the air sealed in the sealant joint after the sealant injection, when the temperature is high (generally higher than 15 ℃), expands in volume, causing the uncured air. Foaming on the surface of the sealant. The probability of such foaming is generally small, and it is obviously affected by temperature. The higher the temperature, the higher the probability of foaming, and the lower the temperature (below 15°C), the lower the probability of foaming.

   The reason for this type of blistering can also be verified by field tests. In the same project, in the same unit plate with the same design size and material, different methods of filling foam rods and different sealants were used, and several field tests were carried out successively. The test results show that after excluding other influencing factors, the main cause of foaming is temperature. When the temperature is high, the probability of blistering is high; when the temperature is low, the probability of blistering is very small. Testing with different batches of sealant yields consistent results and is not directly related to sealant.

Figure 2 Bubbling phenomenon in closed channel

    Since this situation is caused by the expansion of the air sealed in the sealant seam, the most direct solution to this situation is to avoid complete sealing as much as possible. together. If the construction process needs to completely close the sealant joint, pay attention to the possible influence of high ambient temperature or large temperature difference during sealant injection.

(5) Foaming caused by wet interface or accessory material

    This kind of blistering phenomenon is because the interface or accessory material is wet, the moisture penetrates into the sealant seam, and the water vapor volatilizes, resulting in blistering on the surface of the sealant, as shown in the figure below.

Figure 3 Blistering due to wet interface or accessory material

    The probability of this kind of blistering problem is not very large, because there are more thunderstorms in summer, this kind of situation mostly occurs in summer. The solution is: do not construct in rainy days; after rainy days, make sure that the sealant joints and related accessories (such as foam sticks) are dry before construction. If necessary, remove the accessories and wait for the sealant joints to dry and refill before construction.

(6) Foaming caused by construction under outdoor high temperature conditions

    This kind of foaming phenomenon is caused by the construction under high temperature outdoor conditions. Under high temperature conditions, the temperature of the substrate in contact with the sealant is also relatively high, and the reaction is violent, and a large number of bubbles are released in a short time, resulting in the appearance of the sealant surface. blistering phenomenon

Figure 4 Foaming caused by construction under outdoor high temperature conditions

    The probability of such blistering problems is not very large. The solution is to suspend the construction under high temperature outdoor conditions, and wait for the temperature to drop before construction.

    The above summarizes some of the causes of foaming. In actual engineering, the causes of sealant foaming may be more complex and diverse. It may be the combined effect of the above two reasons or multiple reasons, or other possible chemical reactions and gas release. , which needs to be further solved and improved in the continuous sealant application process.

    The foaming mentioned in this article refers to the hollow inside of the sealant and the bulge on the surface of the sealant caused by various reasons, and does not include the phenomenon of “bulging” of the solid inside the sealant and the bulge on the surface of the sealant. The "bulging" phenomenon is the result of the combined effect of the weathering adhesive curing speed, ambient humidity, ambient temperature difference, and the width of the adhesive seam, panel material and size, etc. The inside of the sealant is solid, not hollow, and the phenomenon of foaming needs to be paid attention to. distinguish.

Figure 5 The sealant joint of glass curtain wall is bulging (left) and the sealant seam of aluminum curtain wall is bulging (right)

    The foaming of the sealant results in a hollow part in the colloid. In the foaming part, the actual thickness of the sealant is insufficient, the bonding area may decrease, and the bonding strength will decrease. This has an impact on the construction quality, not only the appearance, but also the waterproof and sealing properties of the sealant to a certain extent. The specific reasons for the foaming phenomenon of sealant are analyzed in the previous article, and most of the reasons are caused by improper construction. Therefore, the author recommends that in the actual construction of curtain wall doors and windows, the training of construction workers should be strengthened, the construction should be carried out in strict accordance with the construction process specifications, and attention should be paid to construction details, which can effectively avoid the occurrence of foaming problems and ensure the construction quality of the sealant.