Hi.

A glue in its container, stays useable until applied, has no exposure to air or whatever makes it 'hard'. Closing the container after use, keeps it useable for still a long time.

 

If the application is between two surfaces, were the glue is confined to similar 'air tight' conditions as it was in the container, it usually hardens as supposed to. What differs in both conditions, inside the container and inside joined impermeable parts ?

Hi.

A glue in its container, stays useable until applied, has no exposure to air or whatever makes it 'hard'. Closing the container after use, keeps it useable for still a long time.

 

If the application is between two surfaces, were the glue is confined to similar 'air tight' conditions as it was in the container, it usually hardens as supposed to. What differs in both conditions, inside the container and inside joined impermeable parts ?

The joined parts often aren't always impermeable. The yellow wood glue is exposed to air because the wood has cavities containing air. The same is true for regular white glue joining paper, wood, leather etcetera.

 

See this article for different glue types and characteristics: >> List of glues

Glues are extremely varied and so are their hardening processes.

Some harden by evaporating the solvent, for instance through the thickness of glued papersheets.

Others harden by a chemical reaction, including with ambient humidity.

Some of the higher end glues are two part that require you to activate it through mixing. This is not something typically found in a home though unless you have hobbies that include Fiberglass or some such.

The other component is moisture in the case of cyanoacrylate glue.