I have seen plastic welding kits @ Harbor Freight but never used & not sure how it works. I think it is just a torch with maybe plastic material as welding rods. I assume you heat the plastic (your crack) to melting point & melt fresh plastic material to the area, but not sure.
Or I would research best material to patch plastic. (Epoxy, Bondo, Fiber Glass body filler, etc) Fiber glass body filler would be my guess, Epoxy may be to brittle for flexing plastic.
To prep surface for old fashion patch I'd...
1. Scuff area with 4" grinder (to give patch rough/clean surface to stick to)
2. Chase crack with the grinder (groove)
3. Drill holes down both sides of crack clear through to allow patch material to ooze out other side. Then mushroom it out to give patch material extra hold.
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Last edited by C Jovingo Landscaping; 10-13-2012 at 10:25 AM.