polyester vs. epoxy for repair
Epoxy has many advantages over polyester. To name but a few:
It''s stronger (higher tensile strength & less brittle)
It forms a much better bond with the substrate. Polyester isn''t even really designed to form a secondary bond.
It shrinks less when it cures.
Its more versatile ie. use of thickeners etc.
A thin film of epoxy will cure, a thin film of polyester may not.
Epoxy can be used at much lower temps than can polyester.
Epoxy has a longer open time.
Epoxy emits little or no toxic fumes.
Epoxy will wet out carbon fiber - polyester won''t.
Cured epoxy is less affected by immersion in water.
Unmixed epoxy has a shelf life measured in years. Polyester is months.
I would say its not necessary to use polyester in ANY type of glass repair. Its just not worth the few dollars you might seem to be saving.