: Is there any secret to prevent fraying of glass?
:

Masking a clean edge, and then trimming the fiberglass cloth at the masked line works well for me. Of course the surface under the fiberglass patch must be dry or at least past the tacky stage.

Vaclav has a nice page explaining this technique (see the link below). Teh photo below is from that page.

Cutting the fiberglass on a bias (diagonally) to the weave as much as possible also minimizes fraying.

John