Definition
A chemical agent added to a resin or other base material to cause it to cure into a solid, rigid form. In aircraft work, hardeners are most commonly used with two-part epoxy and polyester resins for composite layups, fiberglass repairs, and structural bonding.
Plain English
The second part of a two-part glue or resin that you mix in to make it set hard. Without it, the resin stays liquid.
Context Anchor
Seen in aircraft maintenance, especially when mixing epoxy, composite repair materials, sealants, and some paints or coatings.
Derivation
Hardener comes from “harden,” meaning “to make hard.” In aviation maintenance, it names the ingredient that makes another material change from soft or liquid into a firm, usable solid.
Why Pilots Care
Ensures coatings and repairs achieve full strength and resist corrosion or delamination.
Intuition Check
Hardener is not just a stronger or thicker version of the main material. It is the separate part that makes the material chemically set.
Example Sentence 1
He measured the resin and hardener carefully before mixing them for the fiberglass patch on the wingtip.
Example Sentence 2
Using too little hardener left the finish soft and prone to chipping after curing.