Definition
A chemical added to a resin or polymer to start and complete the hardening (curing) process, causing the material to change from a soft, workable state into a solid, finished form with its intended strength and properties.
Plain English
A substance you mix into a resin to make it set hard. Without it, the resin stays soft; with it, the resin turns into a strong solid part.
Context Anchor
Seen in aircraft maintenance when mixing two-part adhesives, repair resins, sealants, or coatings before applying them to an aircraft part.
Derivation
From the older sense of 'cure' meaning to prepare or preserve something through a process (as in curing meat or leather). Applied to chemistry, it describes the process that changes a soft material into its final, hardened state. The 'agent' is the substance that causes this change.
Why Pilots Care
When working with composite repairs, sealants, or two-part adhesives, the correct curing agent and the correct mix ratio are critical. Too little, too much, or the wrong agent can leave the part weak, brittle, or improperly bonded — a real safety issue on structural components.
Analogy
It is like the part of a two-part household glue that makes the mixture actually set. Without it, the material may look mixed but never reach full strength.
Intuition Check
Curing does not mean medical healing here. It means the controlled hardening of a material. Agent does not mean a person here. It means the substance that makes the hardening happen.
Example Sentence 1
The technician carefully measured the curing agent before mixing it with the epoxy resin for the composite patch.
Example Sentence 2
Using too little curing agent left the repair soft and unable to carry structural loads.