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How to Fix a Crack in a Rear Bumper Yourself

by Pearl Lewis

Bumpers are the front line of defense for a vehicle and are designed to be sacrificed to secure the safety of the driver, as well as prevent damage to the vehicle body. It is not surprising that bumpers often sustain damage, even during minor incidents, such as backing into a mailbox. While major collision damage may require bumper replacement, minor cracks and tears can be repaired at home. Body work and collision repairs are expensive, but a cracked bumper repaired at home is likely to cost a fraction of the price you might pay at a repair shop.

Remove the cracked bumper cover from the body of the vehicle. Look for screws on the sides of the vehicle beneath the taillights and in the wheel wells, as well as in the middle, beneath the trunk latch. Lift the trunk carpeting to check for additional screws that attach the bumper cover to the body. Place the bumper on a padded work surface to prevent unnecessary scratching of the surface, and ensure that the work environment is well ventilated.

Use 80-grit sandpaper to roughen the area around the crack on the inside and the outside of the bumper. Clean the area, and remove the particles produced by sanding, both inside and outside, with surface cleaner. Allow the area to dry completely.

Wipe the roughened area with plastic prep solvent to encourage better filler adhesion. Allow the plastic prep solvent to dry.

Measure the crack, and cut and apply an appropriate size piece of self-adhesive fiberglass mat to the back surface of the bumper. Ensure the piece of mat covers the crack with about one inch of excess mat around the crack. The fiberglass mat provides extra support to the damaged area and makes filling the crack an easier process.

Identify the plastic type from which the bumper is made: PP, PPO, TPE, PUR or TPUR. The type is usually engraved or stamped on the inside of the bumper cover. The plastic type determines which filler adhesive to use for the repair.

Follow the manufacturer's instructions for mixing the filler adhesive. Use a smooth-edged plastic or heavy paper spreader card, approximately the size of a credit card, to spread the filler over the damaged area. Apply the first layer, spreading the filler in the direction of the crack. The second layer of filler is applied by stroking across the crack, at right angles to the first stroke, using shorter strokes. Use a clean edge of the spreader card to remove any excess material. Allow the filler to harden.

Use 80-grit sandpaper to remove any uneven bumps, and ensure the filler is flush with the level of the bumper. Polish the repaired area with wet 400-grit sandpaper. Remove any dust particles with a damp rag, and allow the area to dry.

Prepare the damaged area for painting by applying a primer coat. Follow the instructions for application provided by the manufacturer of the plastic primer. Allow the primer to dry and then sand the area lightly with 400-grit sandpaper to promote paint adhesion. Remove dust particles with a damp cloth, and allow the area to dry.

Paint the bumper with plastic paint, following the instructions provided by the paint manufacturer. Apply a second coat of paint, after the first has dried, to ensure maximum coverage of the damaged area. Allow the paint to dry completely, and install the repaired bumper cover on the vehicle.

Warning

  • Chemical inhalation can cause dizziness or fainting. Be sure to work in a well-ventilated area when using solvents, glues or paints.

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About the Author

Pearl Lewis has authored scientific papers for journals such as "Physica Status Solidi," "Materials Science and Engineering" and "Thin Solid Films" since 1994. She also writes an education blog entitled Simple Science in Everyday Life. She holds a doctorate from University of Port Elizabeth.

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  • car dealership 3 image by Alexey Stiop from Fotolia.com