Which method is NOT commonly used for sealant application?

The method identified as not commonly used for sealant application is micro-spray. Sealants are typically applied using methods that allow for controlled placement and consistent thickness, such as brush, spatula, or extrusion guns.

Brushing offers precision while allowing the user to direct the sealant to specific areas, and spatulas facilitate even spreading over larger surfaces. Extrusion guns provide efficient application of sealants, especially in larger volumes or in situations requiring continuous beads, which are critical for maintaining performance under various conditions.

Micro-spray, on the other hand, is not a standard practice for applying sealants in aerospace or similar applications, primarily because it may result in overspraying, inconsistency in application thickness, and potential waste. Consequently, while it might find use in specialized coating processes, it does not align with the typical requirements for sealant application where uniformity and precision are essential.