Definition
An adhesive made from milk protein (casein) mixed with alkaline chemicals, historically used in the construction and repair of wooden aircraft structures. It bonds well to wood but is vulnerable to moisture and fungal attack, and has largely been replaced by modern synthetic resin glues such as resorcinol and epoxy.
Plain English
A type of glue made from a protein found in milk. It was once common in wooden aircraft but is rarely used today because it weakens when it gets damp.
Context Anchor
Seen in maintenance references, repair records, and inspections involving older wooden aircraft or wooden aircraft parts.
Derivation
From the Latin caseus, meaning cheese. Casein is the same milk protein that gives cheese its body, which hints at why the glue is animal-derived rather than chemical and why moisture affects it the way it does.
Why Pilots Care
Knowledge of casein glue helps ensure correct repairs on older wooden airframes where structural bonds must remain reliable.
Intuition Check
Do not assume casein glue is just any strong glue. In aviation maintenance, the material, age, moisture resistance, and approval for the repair all matter.
Example Sentence 1
The mechanic noted that the original wing spar joints were assembled with casein glue and recommended a thorough inspection for moisture damage.
Example Sentence 2
Restorers often replace aged casein glue joints with modern adhesives for improved durability.