Core principle of anti cracking of neutral silicone sealant
After curing, a three-dimensional network structure of high elasticity silicone rubber is formed, which relies on its displacement deformation ability to offset the internal stress caused by thermal expansion, contraction, vibration, and settlement of the substrate, and will not cause hard tensile tearing; Silicon oxygen bonds are resistant to ultraviolet radiation, ozone, and aging, and do not pulverize or crack outdoors for a long time.
Displacement capability (core indicator of crack resistance)
± 25 level: Common for conventional doors and windows, indoor joints, and expandable by 25% of its own length;
± 50/100/50 level: preferred for large panel curtain walls, sunrooms, and color steel tiles with large expansion joints, with a large deformation margin and almost no tearing.
Elasticity index
High quality adhesive has a fracture elongation rate of ≥ 400% and does not break when stretched several times; Low modulus colloids are softer, have lower stress, and have much better crack resistance than high modulus hard adhesives.
chemical stability
Neutral ketoxime/alcohol curing, non corrosive, non corrosive to aluminum, stone, and coated glass, without interface debonding or indirect cracking; Resistant to temperature fluctuations of -50~150 ℃, alternating between hot and cold without cracking.
High tensile strength without fracture
High and low temperature crack resistance test
2、 Select by scenario (specialized anti cracking model)
1) Indoor kitchen and bathroom (moisture-proof+resistant to slight deformation)
Neutral anti mold silicone adhesive (grade 0 anti mold), displacement ± 25 level; Sink, toilet, bathroom corner, with minimal deformation and anti mold and non cracking properties, represented by Wacker SN121 and Baiyun anti mold adhesive.
⚠️ Acidic glue cannot be used to corrode stainless steel and stone, which may cause cracking and detachment in the later stage.
2) External doors and windows, sunrooms, and exterior wall joint filling (high-frequency cold and hot expansion)
Neutral weather resistant silicone adhesive (mandatory)
Conventional doors and windows: ± 25 grade weather resistant adhesive;
Large glass, broken bridge aluminum, sunroom, color steel tiles: upgraded with * * ± 50 grade low modulus weather resistant adhesive * * (Antai 196, Yuhong WS200), with large joint expansion and contraction, completely eliminating seasonal cracking.
3) Curtain wall, large structure expansion joint (with significant displacement)
Neutral silicone structural adhesive/high displacement weather resistant adhesive of grade 100/50, specifically designed for high-rise curtain walls and skylights. The national standard requires high displacement crack resistance and cannot be replaced by ordinary glass adhesive.
4) Severe temperature difference conditions (around the stove and equipment)
High temperature resistant neutral silicone adhesive, long-term 150-300 ℃, does not crack, flow, or become brittle after repeated thermal cycles.
3、 90% cracking is not due to poor adhesion, it is a construction error (key avoidance pit)
- Fatal error: Three sided bonding (most common)
The adhesive sticks to both sides of the gap and the bottom substrate at the same time. When expanding and contracting, the adhesive is locked and cannot be stretched, so it must tear in the middle.
✅ Solution: deep seam is filled with polyethylene foam backing strip, and only two sides of the seam are glued to retain the freedom of deformation. - The size of the adhesive seam is not standardized
Seam width<3mm: There is too little colloid allowance, and slight expansion and contraction can lead to direct breakage; The adhesive layer is too thin (<2mm): there is no elastic buffering; Too thick (>12mm) with incomplete internal curing and internal stress cracking.
✅ Standard: The seam width is 5-10mm, and the adhesive thickness is taken as 1/2~2/3 of the seam width. - Inadequate substrate treatment
There is water, oil stains, dust, and release agent on the seams, and the glue cannot stick firmly. The edges peel off first, and then the entire strip cracks.
✅ Construction: Wipe with alcohol → completely dry before applying glue; Stone and coated glass should undergo compatibility testing in advance. - Disturbance during the solidification period
Before 24 hours of drying and 48-72 hours of complete curing, open and close doors and windows, vibrate, and expose to rain, and the unformed adhesive layer will permanently crack under stress. - Mismatched selection
Indoor ordinary neutral adhesive (with only ± 25 displacement) for large retractable sunrooms, with excessive deformation due to temperature differences between winter and summer, and seasonal cracking every year.
4、 Quickly select crack resistant adhesive and check packaging parameters
Identify 3 packaging labels:
Type: Neutral weather resistant sealant (outdoor)/Neutral anti mold sealant (kitchen and bathroom);
Displacement capacity: ≥ ± 25%, large expansion joint ≥ ± 50%;
Modulus: Low modulus is preferred, with low soft stress and stronger crack resistance.
5、 Cracked Remedial Plan
Whole crack: completely remove the old adhesive, clean it thoroughly, plug the backing strip, and reapply high position neutral weather resistant adhesive;
Surface fine cracks: Cut V-shaped grooves on the surface, apply adhesive and compact;
Edge peeling and cracking: Polish the bonding surface, apply primer to enhance adhesion, and then reapply adhesive.