How to Build Motorcycle Fenders With Fiberglass

by Chris Gilliland

It's not unusual to find fiberglass aftermarket bodywork components. Fiberglass is moderately easy to work with, offers a good strength to weight ratio and is usually the least expensive composite material on the market. Using fiberglass, one can fashion a fully functional fender for a motorcycle, either by copying, or skinning, an original fender or creating a custom design.

Skinning Method

Step 1

Clean the original fender to be copied. Fill in any low spots and sand down rough, raised edges to prevent them from being copied onto your new fender.

Step 2

Apply a a 50/50 mixture of water and white glue to the fender. This will seal the original part and allow the new fiberglass part to be removed easily.

Step 3

Pre-cut your fiberglass material into small strips. This will make it easier for you to place the fiberglass onto the fender in the following steps. Prepare your resin and hardener mixture according to the manufacturer's recommendations.

Step 4

Lay down the first layer of fiberglass onto your original fender, placing the pre-cut strips as close to each other without overlapping. It is okay to let the strips extend past the edge of the fender. If using multiple cloth weights, or thicknesses, start with the heaviest cloth first. This will provide a stronger base for the fender as you build up the layers of fiberglass.

Step 5

Apply your resin mixture to the fiberglass cloth with a paintbrush, using light dabbing motions to saturate the fiberglass cloth. Be careful not to disturb the fiberglass strips. You will notice that the cloth becomes transparent as it absorbs the resin, this is normal.

Step 6

Lay a second layer of cloth onto the fender, overlapping the first layer. This time, dab the cloth lightly without extra resin, using the tip of the brush to compress the second layer against the first layer. Once the cloth has absorbed some of the resin from the first layer, seal it by applying another coat of resin on top of the second layer.

Step 7

Using a plastic spreader or squeegee, remove any trapped air bubbles. Be careful not to move any of the fiberglass layers.

Step 8

Continue layering the fiberglass material and coating with resin epoxy until you have met your desired thickness and allow to cure. The curing process usually takes between 30 minutes to 24 hours.

Step 9

Carefully, remove the new fiberglass fender from the original and test it against the motorcycle for size and fitment. If it fits correctly, cut away excess material and wet sand the exterior until smooth.

Step 10

Drill in any mounting holes as required to fit your motorcycle.

Step 11

Prime and paint your fender before installing it on the motorcycle.

Custom Method

Step 1

Take measurements of your motorcycle's fender mount points. Accurately measure the distance between mounting bolts as well as distance from fork leg to fork leg and tire clearance height.

Step 2

Sketch out your intended fender design, including mounting location details.

Step 3

Shape your new fender using clay or a block of foam by carefully cutting away material. You will only be forming the basic shape of the fender, so it may look a bit unwieldy. Leave enough material to allow for the addition of details and fine-tuning later in the process.

Step 4

Sand the form lightly to further refine the mock-up fender's shape, being careful to keep the form symmetrical.

Step 5

Smooth down any raised edges on the fender's surface and fill any unwanted holes or gaps using body filler.

Step 6

Test the new fender mock-up against the motorcycle to check for proper sizing.

Step 7

Apply a 50/50 mixture of water and white glue to the fender mock-up. This will seal the original part and allow the new fiberglass part to be removed easily.

Step 8

Pre-cut your fiberglass material into small strips. This will make it easier for you to place the fiberglass onto the mock-up in the following steps. Prepare your resin and hardener mixture according to the manufacturer's recommendations.

Step 9

Lay down the first layer of fiberglass onto your fender mock-up. If using multiple cloth weights, or thickness, start with the heaviest cloth first. This will allow for a stronger base for the fender as you build up the layers of fiberglass.

Step 10

Lay down the first layer of fiberglass onto your mock-up, placing the pre-cut strips as close to each other without overlapping. It is okay to let the strips extend past the edge of the fender. If using multiple cloth weights, or thicknesses, start with the heaviest cloth first. This will provide a stronger base for the fender as you build up the layers of fiberglass.

Step 11

Lay a second layer of cloth onto the mock-up, overlapping the first layer. This time, dab the cloth lightly without extra resin, using the tip of the brush to compress the second layer against the first layer. Once the cloth has absorbed some of the resin from the first layer, seal it by applying another coat of resin on top of the second layer.

Step 12

Using a plastic spreader or squeegee, remove any trapped air bubbles. Be careful not to move any of the fiberglass layers.

Step 13

Continue layering the fiberglass material and coating with resin epoxy until you have met your desired thickness and allow to cure. The curing process usually takes between 30 minutes to 24 hours.

Step 14

Carefully, remove the new fiberglass fender from the fender mock-up and test it against the motorcycle for size and fitment. If it fits correctly, cut away excess material and wet sand the exterior until smooth.