Video: Bumper Repair with Hot Air Plastic Welder
This video will demonstrate how to weld plastic using a hot air welder and standard welding rods. As with all plastic repairs, you will need to clean the repair area with plastic cleaner. Put on a heavy wet coat and wipe the area with a clean paper towel. Wipe in one direction to avoid re-contaminating the surface. Use a DA sander with 80 grit sandpaper to remove any coatings that are on the plastic. Remove the paint and any primer that may be beneath the paint until you've exposed bare plastic. Remove paint on both sides of the crack and along the crack line.
After removing all the paint and exposed the bare plastic, blow the dust away with compressed air. Turn the bumper over and clean the plastic with plastic cleaner. If there is any paint on the surface, you will need to remove the paint with a DA sander. Align the damage and apply aluminum body tape. Aluminum body tape is very stiff and can withstand the heat from the welding process. Use a body spreader on the tape to squeeze out the air and maximize the adhesion of the tape. Leave an edge of the tape unstuck to ease removal. Apply tape along the entire crack and especially at the edge, as this is the most difficult part to keep aligned. Use a rotary tool with a teardrop shaped bit. Be sure to round off any sharp edges. From the back of this bumper, we find the symbol TPO.
Look up the symbol in The Book of Plastic Repair that was included with your welder or on the Internet at polyvance.com. We will be using a TPO rod for this repair. Set the temperature of your welder to approximately eight hundred thirty degrees Fahrenheit and wait for the welder to achieve operating temperature. Heat the tip of the rod and the base material with the welder until the rod melts together with the base material. Apply downward pressure on the rod as it is melting. The downward pressure will give the rod better penetration into the base material. Continue melting the rod along the crack line until the crack is completely filled. Allow time for the plastic to cool, then peel the tape from the opposite side.
Use a rotary tool with a teardrop shaped bit to grind a v-groove along the crack line. Be sure to round off any sharp edges. Heat the tip of the rod and the base material with the welder until the rod melts together with the base material. Apply downward pressure on the rod as it is melting. The downward pressure will give better rod penetration into the base material. Continue melting the rod along the crack line until the crack is completely filled. Use a rotary tool with a teardrop shaped cutting bit to grind away excess plastic. Grind the plastic until it is slightly below the level of the surrounding plastic. Use a DA sander and 80 grit sandpaper and sand away the high spots and to abrade the surface. Abrading the surface will help the epoxy filler bond better. Since this plastic is TPO, apply adhesion promoter to any exposed plastic, so that the filler will have a better bond. Parts A and B must be mixed in equal proportions to cure properly. Adding more Part A will not make it cure quicker.
Use a body spreader to mix the two components. Continue mixing until there are no streaks and you have a uniform color. Be careful not to mix air into the filler as this will create pinholes in the epoxy. Apply the filler to the repair area and allow time for the epoxy to cure fully. Even though the epoxy is sandable in about 20 minutes, it is not fully cured. Maximum adhesion is not achieved until the epoxy is fully cured. Cure time can be reduced with the application of heat. Sand and contour the filler to match the profile of the surrounding plastic and finish sanding with 180 grit sandpaper. Sand the area where primer will be applied with 320 grit sandpaper. The tight spots may need to be sanded by hand. Blow the dust away with compressed air or use a tack cloth.
Paint will not stick well to TPO unless an adhesion promoter is applied. Spray a light coat of adhesion promoter on any exposed plastic and allow time for it to dry. Spray primer on any areas that will be top coated..