Definition
The first coating applied to a prepared aircraft surface as part of a finishing system. A primer bonds to the underlying material and provides a chemically compatible base for the topcoat, while also adding corrosion protection to the metal beneath.
Plain English
The first layer of paint-like coating put on a clean, prepared surface. It sticks to the metal and gives the next coat of paint something to grip onto, while also helping to prevent rust and corrosion.
Context Anchor
Seen in aircraft painting, corrosion protection, and maintenance repair instructions before applying the final finish.
Derivation
From the Latin primus, meaning 'first.' A primer is literally the first coat — the one that goes on before everything else.
Why Pilots Care
A sound primer layer prevents hidden corrosion that can weaken structure and ensures the finish lasts through years of weather exposure.
Intuition Check
Do not confuse this with an engine primer, which helps start some engines by adding fuel. In a finishing system, primer is a coating applied to the aircraft surface before the final finish.
Example Sentence 1
After cleaning and etching the aluminum panel, the technician applied a coat of primer before spraying the topcoat.
Example Sentence 2
The technician waited for the primer to cure before applying the topcoat to the fuselage.