How to Repair Fiberglass Fenders

by Jay Kurz

Fiberglass fenders can be an expensive fix if you have to order a brand new one. An easier route is to do the repair yourself. Almost all fiberglass fractures or even holes can be repaired in a quick and relatively easy process. Fiberglass comes in many different forms but for body work the most common is filler. This consists of fiberglass resin that has different materials added to it to increase the volume of the resin. Filler is usually the consistency of putty or peanut butter.

Step 1

Determine if the fender is repairable. Any crack can be fixed, and holes that are 6 inches in diameter or smaller can also be repaired. Any repair using fiberglass filler to a hole larger than 6 inches will not be that strong.

Step 2

Prepare the fender by grinding out any fractures or holes. Carefully grind a the crack into a shallow channel. Sand superficial cracks until they are no longer visible. If there is a hole, sand the perimeter of the hole smooth. The walls of a hole and the walls of a crack should taper gradually for the best bonding results.

Step 3

Wipe the fender clean with a rag and acetone. The acetone will make sure there is not any oil or residue on the surface which could affect the bonding process.

Step 4

If you are repairing a hole or a crack that goes through the fender, use aluminum tape to cover the hole. Stretch the tape tight so that it does not sag into the hole or the crack..

Step 5

Mix the filler with the hardener in the small bucket as directed on the labels. Use a polyester resin for the strongest repairs. You don't have to worry about the color of the resin because you will be painting over it. Mix until the hardener is completely absorbed by the filler. It will be all one color when its ready to apply.

Step 6

Pack the filler into the damaged areas by hand. If you are repairing a hole, remove the fender and set set it on a flat hard surface so the tape does not sag. It is important that there are no gaps between the filler and the fender. Use the putty knife and smooth the filler so that you have a even surface. If the putty sinks in you can add more until its level with the rest of the fender. Let cure until it is hard and cool to the touch.

Step 7

Sand the excess filler down until it's a smooth level surface again. Wear a respirator for protection. You will be able to restore the original surface using this process.

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