There are three forms of silicone sealant cracking: one, cohesion damage, manifested as crack in the middle of the glue seam. Two, bonding failure, shown as the crack on both sides of the glue seam. Three, mixed failure, shown as crack in the middle of the joint and both sides of the crack at the same time. The reasons for cohesive failure and bonding failure of sealant are described as follows:
Cohesion damage
The cohesive damage of weatherproof glue is usually shown as colloidal (sealant in the joint is called colloidal after curing) middle cracking, because the middle is the first to be pulled apart.
Reason analysis:
(1) The quality of sealant
1, in a long time with the continuous precipitation of white oil, resulting in excessive shrinkage of joint colloid, hardness, loss of displacement ability, can not adapt to the displacement of thermal expansion and cold contraction of the base material caused by cracking.
2, the characteristics of oxime type adhesive: poor resistance to joint displacement cracking ability.
3, the content of crosslinking agent in the formula is small, not enough to make the sealant reaction to generate a perfect crosslinking network structure, there are structural defects, easy to lead to colloidal cracking.
4. The sealant is not used within the validity period.
(2) Application reasons
1, the joint design is unreasonable, the joint width is less than 6mm easy to lead to cracking.
2, the formation of a large number of bubbles in the sizing process is easy to lead to colloidal cracking.
3, oxime type sizing is too thin easy to crack.
4, uneven sizing thickness is easy to lead to colloidal cracking in a thin place.
5, when the surface temperature of the substrate is too high or too low, the gel is easy to crack after curing.
6, sealant in the curing process by external force is easy to lead to colloidal cracking after curing.
7, by the action of a large external force or substrate deformation, such as earthquake, typhoon, colloid may crack.
8, three side bonding phenomenon occurs, the amount of displacement sealant can withstand will be limited to ± 15% of the original design displacement, easy to lead to colloidal cracking.
(3) Applicability
1. The displacement capacity of the selected sealant cannot meet the displacement requirements of the joint.
2. The modulus of the sealant chosen does not meet the requirements of the joint.
3, bonding failure.
(4) Application problems
1, the substrate surface cleaning method is improper, the cleaning solvent is not appropriate;
2, the surface of the substrate cleaning can not meet the requirements of sealant, sealant is applied when the surface of the substrate is not volatile dry;
3. The primer used is improper or the primer has failed before use;
4, the substrate surface coated with primer is excessive, the substrate surface is not volatile dry when applying sealant;
5, the sealant in the process of applying the interface sealant is not fully compacted;
6, the contact area of sealant and substrate is too small to ensure the adhesion of sealant and substrate (interface design is not reasonable);
7, sealant in the curing process is affected by the outside world, such as wind load, thermal expansion and contraction of the substrate;
8, construction of the environment temperature is lower than 5℃ caused by condensation and dark dew on the surface of the substrate.
(5) Applicability
1, stone curtain wall has not done the pollution test, can not determine whether the sealant will pollute the base material;
2, metal, stone curtain wall using acid glue will lead to a chemical reaction between the glue and the substrate;
3, glass curtain wall glass and aluminum profile bonding using acid glue, coated glass coated surface bonding using acid glue will lead to bonding failure;
4, before the start of no compatibility test, bonding test and can not ensure the adhesion of sealant and substrate. Contact between chemically incompatible assembly accessories (e.g., seals, spacers, gaskets, fixing blocks, etc.) and the sealant will cause the sealant to discolor or lose adhesion to the substrate.
(6) Quality problems
The displacement capacity, modulus and scalability of the sealant after curing cannot meet the requirements of use. 【 the 】