Reasons For Air Bubbles In Silicone Sealants

The formation of bubbles in silicone sealant during construction can be attributed to various reasons, including the following:

1、Air Entrapment During Application: When workers apply sealant on scaffolding, the operating environment limits the uniformity of application, making it easy for air to become trapped in the sealant joint. During joint finishing, the compressed air generates an outward expansion force, causing the uncured, soft sealant joint to bulge and form bubbles. This phenomenon is more common in high-movement capability weather-resistant sealants. To avoid this issue, it is recommended to apply the sealant from the bottom upward to reduce bubble formation.

2、Moisture at the Interface During Application: During outdoor construction, if the interface is not completely dry after rainfall and sealant is applied, sunlight can cause moisture within the interface to evaporate, pushing up the uncured sealant joint and forming bubbles. Additionally, damp polyethylene foam backing rods may also cause bubbling in the sealant joint.

3、Foam Backing Rod Breakage: Closed-cell polyethylene foam backing rods are typically used in sealant joints. If the rods are improperly compressed during installation, internal air pockets may rupture and release air, leading to bubbles after sealant application. Furthermore, the ethanol released during the curing of alcohol-based weather-resistant sealants may react with certain foam rods, also causing bubbles. Solutions include cutting the foam rod and placing the cut side inward or switching to open-cell foam backing rods.

4、Sun Exposure Before Curing: Immediate exposure to sunlight after sealant application can cause honeycomb-like bubbles to form inside the sealant joint, resulting in external bulging. To avoid this, it is recommended to apply sealant on the west or north side of the building in the morning and on the east or south side in the afternoon, allowing the sealant surface to skin over before sun exposure.

5、Large Day-Night Temperature Differences and Thermal Expansion/Contraction of Interfaces: Aluminum has a high thermal expansion coefficient, and large aluminum panels undergoing repeated thermal expansion and contraction during curing can cause bubbling in the sealant joint. It is advisable to avoid applying sealant during midday when sunlight is strongest to minimize bubble formation.

6、Dry Winter Climate in Northern Regions: Silicone weather-resistant sealants require moisture from the air to cure. In the dry winter climate of northern regions, the curing time is prolonged, and uncured sealant joints are more susceptible to environmental influences, leading to bubble formation.

7、Chemical Reaction Between Substrate and Sealant: Certain chemical additives in cement or concrete may react with the sealant, causing bubbles. Compatibility tests should be conducted before construction, and if necessary, a primer should be used to separate the substrate from the sealant to prevent chemical reactions.