Home » Blog » Why are secondary silicone sealants for insulating glass cracking?

Why are secondary silicone sealants for insulating glass cracking?

Generally, silicone sealant as a secondary sealant for insulating glass, cracking in three forms: cohesion damage, manifested as cracking in the middle of the sealant seam; bonding damage, manifested as cracking on both sides of the sealant seam; and mixing damage, manifested as cracking in the middle of the sealant seam and the two sides of the cracking at the same time. Truemei mainly explains the reasons that lead to the cohesion damage of the sealant and bonding damage.

Sealant cohesion damage is usually manifested as cracking in the middle of the gel

Sealant quality problems

  1. A long time with the continuous precipitation of white oil, caused by excessive contraction of the joint colloid, stiffness, loss of displacement capacity, unable to adapt to the substrate thermal expansion and contraction of the displacement caused by cracking.
  2. The formula of the crosslinking agent content is small, not enough to make the sealant reaction to generate a perfect cross-linking network structure, there are structural defects, which can easily lead to gel cracking.
  3. Sealant is not used within the validity period.

Sealant construction problems

  1. The joint design is unreasonable, the joint width is less than 6mm easily leads to cracking.
  2. The formation of a large number of bubbles in the process of sizing can easily lead to gel cracking.
  3. Uneven thickness of sizing will easily lead to cracking of the gel in thin places.
  4. The surface temperature of the substrate is too high or too low when the construction, the gel curing gel is easy to crack.
  5. The sealant in the curing process by external forces can easily lead to curing gel cracking.
  6. Subject to large external forces or the substrate to produce large deformation, for example, earthquakes, typhoons, etc., the gel may crack.
  7. A Three-sided bonding phenomenon occurs, the sealant can withstand the displacement will be limited to the original design displacement of ± 15% or less, which can easily lead to gel cracking.

Sealant applicability issues

  1. The joint design is unreasonable, the width of the joint is less than 6mm easily leads to cracking.
  2. The formation of a large number of bubbles in the process of sizing will easily lead to colloid cracking.
  3. Uneven thickness of sizing will easily lead to cracking of the gel in thin places.
  4. If the surface temperature of the substrate is too high or too low when the construction, the curing of the gel is easy to crack.
  5. The sealant in the curing process by external forces can easily lead to curing gel cracking.
  6. Subject to large external forces or the substrate to produce large deformation, for example, earthquakes, typhoons, etc., the gel may crack.
  7. A three-sided bonding phenomenon occurs, the sealant can withstand the displacement will be limited to the original design displacement of ± 15% or less, easily lead to gel cracking.

Sealant bonding damage is usually manifested as peeling of the substrate from the sealant

Sealant application problems

  1. The substrate surface cleaning method is not appropriate, cleaning the use of solvents is not appropriate;
  2. The substrate surface cleaning does not meet the sealant application requirements, the application of sealant when the substrate surface is not volatile dry;
  3. The use of the primer is not appropriate or the primer has failed before use;
  4. Substrate surface painting of the primer is too much, the application of sealant when the surface of the substrate is not evaporated dry;
  5. Sealant in the process of application of sealant in the interface is not fully compacted;
  6. The sealant and substrate contact area is too small to ensure the adhesion of sealant and substrate (interface design is unreasonable);
  7. Sealant in the curing process by external influences, such as wind load effect, thermal expansion and contraction of the substrate;
  8. Construction of the ambient temperature below 5 ℃ caused by the substrate surface condensation and dark dew.

Sealant applicability issues

  1. The stone curtain wall did not do a pollution test, can not determine whether the sealant will pollute the substrate;
  2. Metal, stone curtain walls using acidic sealant will lead to a chemical reaction between sealant and substrate;
  3. Glass curtain wall glass and aluminum profile bonding using acidic sealant, coated glass coating surface bonding using acidic sealant will lead to bonding failure;
  4. No compatibility test, or bonding test before the start of work and can not guarantee the bonding of sealant and substrate. Chemically incompatible assembly accessories (e.g., sealing strips, spacer strips, gasket strips, fixing blocks, etc.) in contact with the sealant will lead to discoloration of the sealant or loss of adhesion between the sealant and the substrate.
Share your love