What is a sealant used for?

• A. An insulating medium used wet on bolts, screws or rivets to stop mating surfaces contacting, thereby causing dissimilar metal or galvanic corrosion.
• B. A lubricant applied to fasteners to reduce friction.
• C. A decorative coating for exterior panels.
• D. A sealant used to attach panels permanently with no movement.

Answer: (A)

Sealants in aviation are used to seal joints and insulate mating metal surfaces, preventing moisture and electrical contact between dissimilar metals. When different metals are in contact in the presence of an electrolyte (like moisture), galvanic corrosion can occur, with the more anodic metal corroding faster. Applying a sealant around bolts, screws, or rivets keeps the surfaces apart and blocks the conductive path, reducing or preventing galvanic corrosion. It’s often applied in a pliable, wet state so it can penetrate gaps and form a durable barrier as it cures. The other options describe lubrication, decorative coating, or permanent bonding, which do not address the corrosion-protective insulation sealants provide.