Why does window and door glass fog up? Various reasons...
Release date:
2025-09-01
The basic manufacturing process of insulated glass involves steps such as glass cleaning, molecular sieve filling, application of butyl sealant, lamination, and finally, the application of a second sealing layer. Each step is closely tied to material selection, the skill level of operators, and the overall quality of the production process.
Glass cleaning
Cleaning the glass is the first step in hollow glass production—and one of the most critical steps to ensure the airtightness of the final product. If oil stains and sweat on the glass aren’t thoroughly removed, the adhesive strength of the sealant to the glass will significantly weaken, ultimately compromising the sealing performance of the hollow glass. Unfortunately, in current manufacturing practices, many producers—especially smaller companies—often fail to prioritize proper glass cleaning, leading to a high number of substandard products entering the market.
Desiccant Selection
When selecting a desiccant, it’s essential to consider its properties comprehensively. The choice of desiccant is directly linked to the type of hollow glass sealant being used and should be evaluated in conjunction with it.
Failure of the edge seal in insulated glass units means that doors and windows lose their intended functionality. Not only does this result in inadequate energy efficiency, but it also prevents consumers from clearly seeing outside through the foggy air layer, compromising the transparency of the glass and reducing its thermal insulation performance. Prolonged condensation can lead to mold growth or alkali buildup on the inner surface of the glass, causing unsightly white spots and severely affecting the aesthetic quality of the insulated glass. Clearly, choosing a high-quality insulating glass sealant is essential to preventing condensation from forming in the first place.
The selected hollow glass sealant must meet national or industry standard requirements, and the first and second sealing layers of the double-glazed unit should be compatible—specifically, they must not dissolve into or react with each other. Failure to do so could lead to contamination of the glass surface, potentially accelerating its aging process.
Double-layered hollow glass coating
Laminating is the crucial intermediate step in manufacturing double-glazed hollow glass. The application of butyl sealant before lamination directly determines the overall quality of the hollow glass. If there’s a gap between the two sealing layers, it can lead to air leakage. Additionally, care must be taken to avoid applying the second sealing layer too thinly. Over time, after installation and exposure to fluctuating environmental temperatures, sunlight, and wind pressure, the sealant may develop cracks. Even tiny cracks can allow moisture to gradually seep into the sealant layer, causing condensation and ultimately compromising the sealant’s ability to maintain its airtight performance.
Summary
Apart from a few legitimate hollow glass manufacturers experiencing condensation issues due to product quality problems, some consumers’ one-sided pursuit of low-priced products has also created opportunities for unscrupulous traders. These dishonest vendors simply use double-sided adhesive to directly bond two panes of glass together, then apply ordinary, inexpensive silicone sealant—effectively passing off the result as hollow glass. Unfortunately, this so-called "hollow glass" offers no real soundproofing or insulation benefits and, in fact, tends to develop condensation when exposed to humid weather. Once condensation occurs in such makeshift "glass," it typically becomes irreparable and must be replaced entirely.
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