Following window installation, homeowners frequently confront a frustrating defect: "Why is there internal condensation inside the double glazing that cannot be wiped off? Is it caused by sealant defects, or did the aluminum spacer and molecular sieve fail?" Ji'an Screen Mesh delivers a structural failure diagnosis and ranking framework.
1. Primary Conclusion: Aluminum Spacers Do Not Cause Fogging
Internal fogging is exclusively triggered by seal failure allowing water vapor infiltration. The aluminum spacer itself does not dictate whether insulated glass fogs up. The sequential inspection priority for fogging is strictly: Butyl Sealant ＞ Silicone Sealant ＞ Molecular Sieve.
2. Three Critical Factors Governing Insulated Glass Condensation
| Component Stage | Engineering Standard | Failure & Fogging Mechanism |
|---|---|---|
| Primary Sealant (PIB Butyl) • Core Moisture Barrier | Applied to spacer flanks; national specifications require a thickness of 3mm. | Many fabricators apply only 2mm or less. Uneven or thin application causes butyl discontinuity and voids under press compression, failing to block vapor; or using low-content butyl tape substitutes. |
| Secondary Sealant (Silicone) • Structural Protection | External structural barrier blocking liquid water droplets and securing glass units. | Silicone features a microporous structure that cannot stop vapor penetration; if silicone contains white mineral oil, it reacts chemically with butyl, causing the primary barrier to dissolve and liquefy. |
| Adsorbent Media (Molecular Sieve) • Final Moisture Defense | Requires a static water adsorption capacity of ≥16% (standard 3A zeolite). | Nearly 80% of units use budget desiccant (Class B) with only 10%–11% capacity (1/3 less capacity, half the cost) and underfill spacers; fogging occurs as soon as moisture exceeds adsorption capacity. |
3. Sourcing Recommendation
To eliminate internal glazing condensation, strictly verify continuous butyl application (≥3mm), specify certified 3A molecular sieves, and eliminate white oil silicone sealants. Pair premium aluminum spacers from Ji'an Screen Mesh with dual-seal protocols for durable insulated units.