Damage to the bumper that reaches the surface of the polyporpylene cannot be fixed just by painting. Use the repair methods shown below to repair damage that reaches the surface of the polypropylene.
1. Rough cut the damaged area 45º using a knife and then sand the angle smooth.
2. Welding damaged area
3. Melt polypropylene welding rod using a heat gun and fill in the cracked area.
4. Grind polypropylene surface carefully. It melts easily due to the heat generated by friction. If melted, remove that area. Also, grind the area where solvent is to be applied.
5. Apply polypropylene primer evenly with a brush over an area wider than the area to be repaired.
Dry it at 20ºC (68ºF) for more than 10 minutes.
6. Mix main filler material and hardener at a ratio depending on paint specifications. Mix filler material and apply over the damaged area.
When the filler material hardens, you will have a desirable finish with flexibility like polypropylene.
7. Sand the damaged area with sandpaper using #180~#240 grit paper.
8. Degrease the painted surface.
9. Mix polypropylene primer and hardener at a ratio depending on paint specifications.
Spray polypropylene primer on the surface of the damaged area and the bumper.
10. Apply polypropylene primer.