Comments by "Drew Hodge" (@drewhodge3820) on "Best Plastic Welder? Weld Repair Stronger Than New? Let’s find out!" video.

You don't start plastic welding on the surface when doing butt welds You have either grind out a bevel (V grove) or melt a bevel into to the areas being welded. The same way you bevel metal when welding thick material. So like metal welding you then back fill the bevel with the welding material. That method especially applies to the plastic welders that have a central feed tip for the welding rods. Then the additional strength comes from the metal staples or mesh that should be melted into the surface plastic your trying to join. Surface welding isn't the strongest but some times it's the only option. You still need to preheat the crack/joint in the plastic before welding to get the best penetration weld, especially with thicker plastics.
1