Endurcir belong to the 2
nd group.
Endurcir is conjugated the same way that verbs that end in :
-ir
Endurcir is conjugated with
auxiliary avoir.
Endurcir verb is direct transitive.
French verb endurcir can be conjugated in the reflexive form:
Endurcir verb is a direct transitive verb, so ive voice can be used.