Its just fibreglass, if you can do paper mache from elementary school, you can do glass work.
Go to west marine, or any boat/marine supply store, and get yourself some glass mat and some 2 part epoxy, or vinyl ester resin, or whatever they have in stock for cheap.
Get the gate on a flat surface/horizontal.
Grind out the damaged section. Use a 10 to 1 taper. Meaning if the thickness of the repair is 1/4", then you need to grind out about 2.5 inches tapering up.
Hot glue, tape, whatever, a solid piece of wood to the inside of the gate so you have a backing to work against. Put a piece of wax paper on the wood so the resins dont stick to it and glue that wood to your gate hahah.
Cut out pieces of the glass to fill the hole, getting larger and larger until you've built up the hole to the level of the painted surface. Do a little more than you think you need and leave it a little tall.
Now mix up your epoxy/resin. Wet each piece of glass with the resin and lay it in place, and roll/squeegee any air bubbles out. Keep doing each piece of glass until you've filled the repair area. Let dry overnight, sand flat and reinstall hardware and paint.
You can then reinforce the INSIDE of the gate in the high stress areas by just adding more glass and resin and build it up. Dont get too thick tho, as I believe the gate latch can only handle up to a certain thickness.
Sounds hard, but any grade schooler can do it, its alllllllll in the prep work tho.
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