How do I Weld & Repair Motorcycle Plastic?

Written by chris stevenson
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How do I Weld & Repair Motorcycle Plastic?
Repairing fenders and farings is easy with a plastic weld kit. (motorcycle image by Goran Bogicevic from

Motorcycle fenders can sustain damage just like any other part. Although plastic fenders have been designed to absorb impact, sometimes the damage they suffer can result in cracks and tears. Rather than replace the fender or fairing, the motorcycle owner has a few options. One of those options can be a plastic welding kit designed to restore the plastic damage back to its original condition. Repairing your own fender damage can be accomplished by the average motorcycle owner. He needs only to find the right plastic repair kit, gather a few tools and learn some repair procedures.

Skill level:

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Things you need

  • Socket set and wrench
  • End wrenches
  • Sponge
  • Dish washing soap
  • Putty knife
  • Drill motor and bits
  • Plastic cleaner
  • Plastic weld kit
  • Plastic adhesive
  • Sandpaper
  • Sanding block
  • Flat file
  • Fibreglass patch
  • Masking tape
  • Primer
  • Paint

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    How to use Motorcycle Plastic Weld

  1. 1

    Remove the damaged plastic motorcycle panel, such as a fender or fairing, using the proper size socket or end wrench. Secure the piece in a wide-jaw vice, or make it immobile with supports so you can work on it. Use a sponge, soap and water to clean the area to be fixed. Mask off the undamaged area.

  2. 2

    Locate the inside of the crack's end. Use the drill motor and a small bit, 1/8-inch or smaller, to drill a small hole at the end of the crack--this will stop the crack from spreading. Surround the entire crack with drill holes on all sides. Space the holes about 1/4-inch apart and 1/4-inch away from the crack. Run the drill bit up the crack channel to widen it until you reach the end.

  3. 3

    Sand the damaged area with heavy 220-grit sandpaper. Sand a crosshatch pattern back and forth. Sand the inside of the damaged panel in the same manner. Clean both sides of the piece with plastic cleaner and wipe dry. Cut a patch of fibreglass mat to the size of the damaged area, overlapping by at least 1-inch on all sides. Cut it flush with the outside edge of the damaged piece.

  4. 4

    Soak the fibreglass patch in plastic adhesive and apply it to the underside of the crack. Let it dry completely. Turn the piece over. Mix the contents of the plastic weld according to directions. Spread the plastic weld on the surface of the damaged area. Press it down hard with the putty knife so the material enters the drill holes and all air has been removed. Build up the putty slightly higher than the surface of the plastic. Apply a thin layer of plastic weld putty to the inside of the piece. Let it dry completely.

  5. 5

    Shave off the outside surface of the piece using a flat file, taking the height of the putty down nearly to the surface. Finish sanding the piece with a fine 400-grit sandpaper wrapped around a sanding block. Smooth until desired finish has been obtained. Clean the piece with plastic cleaner. Apply appropriate primer coat and paint to match finish.

Tips and warnings

  • Leave the built-up plastic weld on the inside of the damaged piece--do not sand or file. This will add backing strength.
  • An alternative method of repair involves the use of plastic glue directly in the crack, and C-clamps to hold it in place. This method will not be as strong as the patch method, but can work on smaller cracks and splits.

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