How to Make a Mold for a Fender

Fiberglass molds allow you to create multiple copies of a particular car part. Making a mold from an existing fender will allow you to make numerous identical fenders from that single mold. Such a mold can be used to craft fiberglass car or truck fenders. It is a less expensive option than purchasing factory-made replacement fenders. With a two-sided mold that meets at the center, you can mold both sides of the three-dimensional fender in a single mold.

Instructions

1

Clean and polish the fender you will be using to craft your mold. Any dents or imperfections should be removed, as these will transfer over to the mold and any fenders made from the mold.

2

Coat the fender with four coats of parting wax. Mist the coated fender with three coats of PVA release film. Add parting flanges or dams to what will be the parting planes of the mold or the spot where the two halves of the mold meet. You can cut strips of poster board to use as parting flanges or roll a snake of modeling clay and apply it to these portions of the fender.

3

Use a cup gun to apply a polyester tooling gel coat to the coated fender. The finished gel coat should have a thickness of 20 to 25 mils consisting of three coats of 7 to 8 mils. The coats need to be applied continuously. Do not allow one coat to harden before the next coat is applied.

4

Apply the 1.5-ounce fiberglass mat to the coated fender as a stabilizing layer, using epoxy. This layer should be added between 90 minutes and five hours of when the last of the gel coat was applied. Allow the mat to cool before adding additional layers.

5

Sand the mat. Apply resin followed by additional layers of fiberglass mat. Two to three layers of fiberglass mat can be applied at a time. Use a bristle roller or grooved saturation roller to roll out the air bubbles every few layers before more resin and mat is applied. In total you will need about eight to 10 layers of mat.

6

Strip off the parting flange. Apply parting release wax to the flange on the mold.

7

Follow the steps above to create the second half of the mold that will match up with the first mold.

8

Remove the mold from the original fender using a mold release wedge. Wedges should be inserted between the mold and the fender and gently tapped to separate the mold and the fender. Pressurized air or a rubber mallet can be used to assist in separating the mold and fender.