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How To Mould A Body Kit To Your Car - And Should You Do It?

January 28, 2019

How To Mould A Body Kit To Your Car - And Should You Do It?

Moulding a body kit to your car may appear like something that anybody can do, but it is a complex process that ought to be done by someone who is experienced in doing this kind of work.

In most cases, body kit parts do not fit as perfectly as OEM parts; some sections of the body kit parts may be slightly longer or wider, and may even have minor scuffs. You’ll need to know how to heat, re-shape, shave, fill, and paint an array of different body kit materials. You also need to know how to prepare the exterior of your car to fit the body kit parts.

Needless to say, it is easy to make a mistake - and making a mistake in body kit moulding may mean having to redo everything. If you are not experienced in moulding body kits, you should at least do it with the help of someone who has experience doing this kind of work.

Working with Body Kit Materials

For the most part, the car body kits currently available on the market are composed of a varied selection of the following materials: ABS plastic; polyurethane (urethane); fiberglass; carbon fiber; or composite forms of the those materials. Each of these materials should be handled differently.


Fiberglass is fiber-reinforced plastic that incorporates many small glass fibers, and as such, it is quite brittle. Excessive bending or moulding can cause cracks. Fiberglass body kits demand a lot of prep work when moulding. Preparation is required for both the fiberglass parts and also the surfaces on the car where they will be fitted.   

ABS Plastic

ABS Plastic is less brittle than fiberglass, so it is easier to work with. However, you must be careful when working with ABS Plastic because it tends to absorb heat and melt easily. Excessive sanding using power sanders can cause the material to split and melt into hair-like strands.

Carbon Fiber

Carbon fiber body kits are very rigid, so reshaping them without causing them to break is almost impossible. However, you can trim or cut them. Also worth noting about carbon fiber parts is that you may not need to paint them. The parts already feature clear-paint coating, and you probably won’t want to hide the appealing look of their weaved carbon fibers. 


Polyurethane body kits are arguably the easiest to work with because they are flexible, and also because they tend to fit just right. These kits can be easily bent or coaxed into the right position.

How To Mould Your New Body Kit

Now that we know about the materials involved, let’s look at the necessary steps to successfully mould a body kit to your car:

1. Dry-fit the Kit

After you receive your body kit parts, you should first dry-fit them on your car to see the pieces align. Dry-fitting means positioning and aligning the body kit parts as you would want them to be when the work is done.

Dry-fitting will help you to see the gaps that you need to fill, and the adjustments that you need to make on the different body kit parts. It also helps you to take note of cracks or other defects on your car that you may need to deal with first, before fitting the body kit part. You may need to drill screws to hold the body kit parts in place.

While the body kit parts are still on your car, use tape to mark the edges and ends of the body kit parts on your car; this will guide you when you start to prepare the designated surfaces of your car for the actual fitment of the body kit.

2. Cracks, Gaps, and Sanding

After marking the edges of the body kit parts on your car, remove the body kit parts and attend to the gaps and cracks that you may have noticed. If there are any cracks or seams in the marked areas, you’ll need to use an epoxy adhesive to cement them. If there are gaps or dents, you may need to apply body filler to close those openings.

After applying adequate amounts of body filler and smoothing it out, wait for it to dry. When dry,  do some good sanding to cut all the high edges down. It is wise to use a good quality air sander to ensure that high-quality trimming down of the edges and smoothing the surfaces.

After using the air sander, you can further smooth the surfaces doing block sanding by hand. The best way to do block sanding is by doing criss-cross sanding motions across the taped surfaces. As you continue to do the sanding, you can stop at certain points, and dry-fit the different body kit parts to see how much more sanding you need to do.

Once you are done sanding the taped surfaces, you’ll need to block sand the body kit part surfaces that are going to be glued to your car. The way you’ll do this part depends on the type of body kit material you’re working with. 

3. Adhesive and Fitting

After you are done with sanding, you’ll need to refer to the installation instructions for the body kit, then apply an appropriate epoxy adhesive as directed. The best method is to apply the adhesive to both the body kit part and the entire surface on which it is going to be placed. Once the adhesive is in place on both surfaces, fit the body kit part onto the car. You’ll need to hold the part in place until the adhesive dries. 

4. Finishing Touches

After gluing each of the body kit parts onto the car, let them fully dry according to the instruction for the adhesive. Then, sand down the protruding blobs of dried adhesive with a coarse sanding wheel. Do this for all the parts.

Next, use a finer sanding wheel to smooth the edges of the body kit fitments. After that, it is recommended that you apply an additional coat of fiberglass filler along all the edges where the body kit parts join with the car. Following that application is another sanding process that will prepare the car for painting.

Use Experienced Help

As you can see, the body kit moulding process appears relatively simple but is actually rather complex. It’s best to leave it to experienced hands, or to work in tandem with someone who’s done it before so you can avoid mistakes. The end results will be that much better for it.

You can get more information about how to mould a body kit onto a car in the AusBody Works blog. AusBody Works is an established supplier of affordable ABS-plastic and Polyurethane body kits in Australia. You are always assured of the highest quality with our body kits, which all come from top-rated international body kit manufacturers.

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