The plastic welder looks just like a soldering iron.. Its the rods are just strips of the same plastic..
Something i found out the hard way is that my anni valance isn't plastic weldable. As its made using a 2 part chemical. You have to use special rods to effectively Braise not included.. Welding 2 different plastics is hard to do.
I tried plastic welding my bump strip 4 times. first 3 times it cracked!

But stick with it! You will get there in the end
