fixing vs mending

fixing and mending both are nouns.

Word	Noun	Adjective	Verb	Adverb
fixing	Yes	No	No	No
mending	Yes	No	No	No

As nouns, fixing and mending are synonyms defined as:

Other synonyms of fixing include fix, fixture, mend, repair, reparation.

fixing (noun)	mending (noun)
the act of putting something in working order again	the act of putting something in working order again
the sterilization of an animal	garments that must be repaired
(histology) the preservation and hardening of a tissue sample to retain as nearly as possible the same relations they had in the living body
restraint that attaches to something or holds something in place