There are three forms of silicone sealant cracking
Cohesive failure is manifested as cracks in the middle of the glue joint; bonding failure is manifested as cracks on both sides of the glue joint; mixed failure is manifested as cracks in the middle of the glue joint and cracks on both sides.

The following is an explanation of the reasons that cause the cohesive failure and bonding failure of the sealant:
The cohesive failure of the sealant is usually manifested as a crack in the middle of the colloid (the sealant in the glue joint is called colloid after curing), because the thinnest middle is the first to be cracked.

One sealant quality problem

1. With the continuous precipitation of white oil for a long time, it will cause excessive shrinkage, rigidity, and loss of displacement ability of the joint colloid, which cannot adapt to the displacement of the thermal expansion and contraction of the substrate, causing cracking.

2. The content of cross-linking agent in the formula is small, which is not enough to make the sealant react to form a perfect cross-linked network structure, and there are structural defects, which can easily lead to colloid cracking.

3. The sealant is not used within the validity period.

Two application reasons　

1. The seam design is unreasonable, and the seam width is less than 6mm, which may cause cracking.

2. The formation of a large number of bubbles during the sizing process can easily cause the colloid to crack.

3. Uneven sizing thickness can easily cause the colloid to crack in thin places.

4. When the surface temperature of the substrate is too high or too low, it will be easy to crack after the glue is cured.

5. When the sealant is subjected to external force during the curing process, it is easy to cause the gel to crack after curing.

6. The colloid may crack due to large external force or large deformation of the base material, for example, earthquake, typhoon, etc.

7. When the three-sided bonding phenomenon occurs, the displacement that the sealant can bear will be limited to within ±15% of the original design displacement, which will easily cause the gel to crack.

Three applicability issues

1. The displacement capacity of the selected sealant cannot meet the joint displacement requirements.

2. The modulus of the selected sealant does not meet the joint requirements.

3. Bond failure.