Introduction: How to Properly Repair Cracked Plastic Trim
Video tutorial on how to repair cracked plastic trim. A similar procedure can be used on a plastic bumper as well and I will be producing that video in the future. This procedure can be used to repair existing damaged trim or make custom trim. This can be applied to a variety of plastics found on both the exterior and interior of a vehicle, but isn't just limited to automotive applications either. This particular tutorial was done on a 1997 BMW 540i.
- 180 grit sandpaper
- 220 grit sandpaper
- 400 grit sandpaper
- sanding block
- abrasive pad
- rubbing/isopropyl alcohol or degreaser
- soldering iron
- adhesion promoter
- high build primer
- plastic epoxy
- body filler applicator
First step is remove the paint and getting to the raw plastic as we don’t want any contaminants. Use 180 grit sandpaper to remove the paint to expose the bare plastic. Carefully sand the area, depending on the damage you will want to provide some support so the cracked area doesn’t get worse. Use an abrasive pad just to clean any edges with didn’t get or hard to reach areas which will remove any dirt or lightly attached contaminants from the surface.
Just to give you a view where I'm at after sanding. Clean the area using rubbing alcohol, then allow it to evaporate.
Use a soldering iron to tack the crack back together, roughly holding the damaged area. Once satisfied, if your soldering iron has changeable tips, use a flat tip. Now melt the crack back together fully, don't be afraid to stick the soldering iron in the crack so it's not just a surface repair. Some plastics after being melted will take longer to cure than others and is shown by the plastic feeling somewhat softer or rubbery compared to the rest of the plastic piece. Some plastics may take a couple days to cure and the repair won’t be as strong until it has cured. After the plastic has cured, sand the area with 180 grit sandpaper smoothening the repair along with making a slightly lower spot where we will be applying some epoxy filler after for extra reinforcing.
Use an automotive grade flexible epoxy to fill and reinforce the damaged area. Ensure that the epoxy is compatible with the plastic you are working with. Clean the area using rubbing alcohol, then allow it to evaporate. Mix the epoxy accordingly, then apply it using a body filler applicator. Apply more epoxy if needed, allow it to harden, curing times will vary between manufacturers. Once cured, block sand the area with 180 sandpaper to rough out the shape. Using a flexible rubber pad to follow the contour of the trim and 220 grit sandpaper.
Clean the area using rubbing alcohol, then allow it to evaporate. Considering this is plastic, we will need to apply an adhesion promotor. Then apply a high fill primer which will fill in any imperfections in the surface if there is any. Once dry, wet sand the area using 400 grit wet/dry compatible sand paper.
Clean the area using rubbing alcohol, then allow it to evaporate. Apply a paint of your choice, in the video I have used a color matched acrylic enamel single stage paint. You can use a two stage paint as well which involving applying a base color and then clear coat. Color matched paint can be custom mixed at your local automotive parts store.
Allow the paint to dry. Dry times will vary depending on your climate and the paint used. If you wish, you can wet sand the paint to remove any excessive amounts of orange peal, then buff for a mirror shine.