Modifying your car’s bodywork can be a necessity for performance upgrades or simply to achieve a custom look. If you’re facing issues like tire clearance with a new wheel setup, or just want to enhance the aerodynamics of your vehicle, creating custom Fibreglass Car Parts can be a cost-effective and rewarding solution. This guide will walk you through the process of modifying existing fenders using fibreglass, similar to the method I used to help a friend with his Ralt R5 CSR Mazda race car. His larger tires were hitting the stock fenders, leading to an inelegant and inefficient modification. Instead of replacing the entire front bodywork, we opted to craft new fender sections from fibreglass and graft them onto the existing structure. While I don’t have step-by-step photos from that project, I’ve created illustrations to guide you through each stage.
First, determine the extent of the modification needed. For our race car project, we needed to raise the fender line to accommodate the larger tires. Start by creating a template to guide the cutting of the blue foam, which will serve as the base for our fibreglass car part.
Alt: Blue foam template being positioned onto a car fender to outline the area for fibreglass extension, highlighting DIY fibreglass car parts creation.
Using a hot wire cutter, carefully shape the blue foam according to your template. Once cut, place the foam piece on top of the existing fender to ensure it matches the desired shape and fit. This step is crucial for visualizing the final fibreglass car part and making any necessary adjustments before proceeding.
Next, secure the foam mold to the fender using clear packing tape.
Alt: Securing a custom-cut blue foam mold onto a car fender with clear packing tape, preparing for fibreglass application in DIY car bodywork.
The tape acts as a barrier, preventing the polyester resin from dissolving the foam during the fibreglass application process. For this particular project, we also wanted to incorporate vents into the new fender design. We used wooden molding, hot-glued onto the taped foam, to create these vent shapes. This demonstrates the versatility of using foam to create complex shapes for fibreglass car parts.
Alt: Wooden molding hot-glued onto a foam fender extension to create vent shapes for a custom fibreglass car part, showcasing detail in DIY auto bodywork.
With the foam mold prepared, apply a generous coating of mold release wax to the taped surface. This is essential for the successful removal of the fibreglass mold later on and is a key step in creating professional-looking fibreglass car parts.
Alt: Application of mold release wax to a taped foam car fender mold, essential step for releasing fibreglass car parts from the mold during fabrication.
Now it’s time to apply the fibreglass. Saturate fibreglass cloth with polyester resin and carefully lay it over the foam mold.
Alt: Wetting fibreglass cloth with polyester resin and applying it over a foam car fender mold, demonstrating the initial layers of fibreglass car part construction.
You can choose between woven fibreglass cloth or chopped strand mat (CSM). If using CSM, polyester resin is mandatory as epoxy resin won’t properly dissolve the styrene binder in CSM. In fact, using epoxy with CSM will only result in a sticky, unusable mess.
A useful technique for working with woven cloth is to pre-cut the pieces and lightly adhere them to your pattern using 3M Super77 spray adhesive. This helps keep the cloth in place while you saturate it with resin using a short bristled paintbrush. When applying multiple layers of cloth (or CSM), ensure each section overlaps the previous one by at least an inch to maintain structural integrity of your fibreglass car part.
Once the polyester resin has fully cured, carefully peel the fibreglass mold away from the foam pattern.
Alt: Separating a cured fibreglass mold from a foam pattern after resin hardening, revealing the initial fibreglass car part shape formed.
To create a carbon fiber positive from this fibreglass mold, the process continues. First, apply another layer of mold release wax to the inner surface of the fibreglass mold.
Alt: Applying mold release wax to the inside of a fibreglass mold to prepare it for carbon fibre molding, a step in creating advanced composite car parts.
Begin layering carbon fiber cloth inside the fibreglass mold, wetting each layer with epoxy resin. When applying the resin, use a short bristled brush and a stippling motion to ensure the resin fully permeates the carbon fiber cloth as it conforms to the mold shape. I recommend using epoxy resin for carbon fiber lamination as it results in a significantly stiffer and stronger final fibreglass car part, or in this case, carbon fiber part.
Alt: Layering carbon fiber cloth and epoxy resin inside a fibreglass mold to form a carbon fibre car part, illustrating the molding process for composite auto components.
For optimal strength, apply layers of carbon fiber cloth at alternating 45/90 degree angles. Woven carbon fiber is only stiff along its fiber orientation, so this cross-ply technique maximizes the rigidity of the fibreglass car part.
Before the epoxy resin completely hardens, trim any excess carbon fiber material around the edges of the mold using scissors.
Alt: Trimming excess carbon fiber material from the edges of a mold with scissors before the resin fully cures, streamlining the finishing of carbon fibre car parts.
Trimming at this stage is significantly easier than after the resin has fully cured.
Once the resin is fully cured, the finished carbon fiber part can be removed from the fibreglass mold.
Alt: Removing a cured carbon fibre car part from its fibreglass mold, showcasing the final shape and finish of a DIY composite automotive component.
After demolding, the final step involves bonding the new carbon fiber fender sections onto the existing car bodywork. Use a suitable bonding agent and blend the seams smoothly using body filler for a seamless, professional finish. This completes the modification process, resulting in custom fibreglass car parts (or carbon fiber parts, depending on your chosen material) that enhance both the function and aesthetics of your vehicle.
Alt: Bonding a new carbon fibre fender section onto an existing car body and blending it with filler, finalizing the custom fibreglass car part installation and bodywork integration.
