Reference: Abbott, Richard. Analysis and Design of Composite and Metallic Flight Vehicle Structures 3 Edition, 2019
Jointing compounds are used for protection at joints where they act by excluding dirt and moisture, and by providing a reservoir of slightly soluble chromates which act as inhibitors. Sealants are applied to joints to prevent the escape of fluids, such as fuel, but they also exclude moisture.
Common aircraft fay surface and joint sealing products are typically qualified to MIL-S-8802. These sealants are commonly used for both joint surface and edge sealing as well as for sealing fuel tanks. Note that a liquid shim also acts as a surface seal.
Sealants can be both conductive (for grounding and lightning strike protection) and non-conductive (for electrical isolation and protection against galvanic corrosion).
Temperature resistant sealants for firewall applications are typically qualified to MIL-S-38249.