1. Quality requirements for structural adhesive

There are many indicators for structural adhesive, and it is generally believed that there are four essential properties: good adhesion, sufficient strength, appropriate displacement ability, and long-term durability. To meet the four elements, a specially formulated silicone adhesive must be used.

The strength and displacement capacity of structural adhesive are interdependent, and the displacement capacity decreases with increasing strength, and vice versa. Therefore, a special formula of structural adhesive is required to meet both of these indicators simultaneously.

2. Quality requirements for weather resistant adhesive

2.1 Weathering adhesive should also have four basic characteristics: good and durable adhesion, a certain modulus, appropriate displacement ability, durability, and protection of building appearance.

The importance of adhesion is self-evident. Non adhesion with the substrate is one of the reasons for building water leakage. Good expansion performance means lower modulus and good displacement ability.

2.3 A lower modulus surface sealant will generate less stress on the interface during stretching, which is beneficial for the long-term adhesion of the sealant. Good displacement ability means that the sealant is less likely to crack due to excessive displacement of the plate interface.

The service life of sealant depends on its durability and cannot crack due to ultraviolet radiation; Also, improper use of sealant can affect the aesthetics of the building. The pollution and sagging caused by sealant are very obvious and lack aesthetic appeal.

3. Quality inspection of sealant

(1) The structural adhesive must have cohesive failure.

1.1 The cross-section of the structural adhesive cut should have uniform color, and the adhesive injection should be full and dense.

1.2 The injection width and thickness of structural adhesive should meet the design requirements, and the width should not be less than 7mm and the thickness should not be less than 6mm.

1.3 A cutting surface should be made perpendicular to the adhesive, and two vertical cutting surfaces with a length of about 50mm should be cut along the substrate surface from this cutting surface. The silicone structural adhesive block should be manually pulled in a direction greater than 90 °, and the damage to the peeling surface should be observed.

1.4 Observe and inspect the quality of the adhesive, measure the thickness and width of the adhesive with a steel ruler with a division value of 1mm.

（2）. The quality inspection of weather resistant adhesive should comply with the following regulations

2.1 The surface of the weather resistant adhesive should be smooth and free of cracks, and the thickness and color at the interface should be consistent.

2.2 The glue injection should be full, smooth, dense, and seamless.

2.3 The bonding form and width of weather resistant adhesive should meet the design requirements, and the thickness should not be less than 3.5mm.

2.4 The inspection of weather resistant sealant should be carried out through observation and cutting inspection methods, and the width and thickness of the sealant should be measured using a vernier caliper with a resolution of 0.05mm.

4. Building rainwater leakage caused by sealant reasons

Improper construction, including missing silicone, cutting corners or not following the drawings during construction, and not filling the interface with sealant, can lead to waterproof failure, which is more lethal.

4.2 When external forces, gaps, and water factors coexist, water leakage is inevitable. Leakage of silicone, cutting corners, or not following the drawings during construction can cause poor sealing and water leakage. At the same time, it should be noted that the sealant should fill the entire interface and fully contact the substrate to ensure good adhesion between the sealant and substrate, which is also one of the prerequisites for the durability of the sealant.

4.3 If the displacement capacity of silica gel fails to reach the displacement capacity of the interface, it will inevitably lead to poor weather resistance of the sealant, insufficient anti-aging capacity and other consequences. However, the displacement capacity of the sealant will be significantly reduced after aging. The reason why the displacement capacity of the plate cannot be met is that the sealant with low displacement capacity is used, or even the fake sealant.

4.4 Because the three sided bonding will limit the displacement ability of the sealant, it is necessary to use anti adhesive tape to avoid three sided bonding. The joint at the junction has a large displacement due to different forces, so it is important to reserve expansion joints in the design to allow the sealant to bear the excessive displacement and avoid direct collision between the window frame and the wall.

5. Structural assembly failure caused by sealant reasons

The common cause of structural assembly failure is bonding failure, which is also the most common reason. Bonding failure indicates that the structural adhesive is ineffective and also means assembly failure.

5.2 Untreated materials have a large amount of foreign matter adhering to their surfaces, which can affect the establishment of adhesion if not effectively cleaned. However, there are also certain differences between the types of bonding and cleaning solvents. Cleaning substrates with different cleaning solvents results in significantly different bonding strengths, so solvents should also be selected through adhesion testing.

5.3 Interface design is also very important in structural assembly. In addition to meeting the requirements for the width and depth of the structural adhesive, the ease of construction and the curing characteristics of the sealant are often overlooked. This is the main reason for the failure of most structural assemblies. Improper design not only makes it inconvenient to apply silicone, but also makes it difficult to fill the interface and clean. Therefore, the adhesion of silicone adhesive cannot be guaranteed. If a separate interface design is adopted, the double-sided adhesive strip with spacing effect is placed near the four sides of the glass, and the weather resistant adhesive of the structural adhesive is separated, so that its construction and curing are not affected by each other.