How to use fiberglass to make a body kit

Written by ryan bauer
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How to use fiberglass to make a body kit
A project that's probably not for a novice. (

If your car's stock look has you yawning every time you look at it, maybe it's time to spice things up with a body kit. Sometimes commercial body kits just aren't what you're looking for or are simply out of your budget. In that case, making your own out of fibreglass can make a lot of sense. While anyone can make a fibreglass body kit, making one that looks good is an entirely different story. If you don't have any fibreglass or auto body experience, you might want to skip this project. Otherwise, this is one of the most rewarding tasks you can take on.

Skill level:

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Things you need

  • High-density Foam
  • Fibreglass sheets
  • Fibreglass matt
  • Aluminium foil
  • Pan spray
  • Bondo
  • Carving tools
  • Measuring tape
  • Electric sander
  • Glue
  • Primer
  • Colour matched paint

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  1. 1

    Sketch your design. Without getting your layout on paper first, your body kit is almost guaranteed to look terrible. This is the place to let your artistic side run wild. Get an idea of what you want by looking at existing body kits, and put your favourite aspects of each one into your design.

  2. 2

    After removing the existing bumpers and trim on your car, cut lengths of high-density foam into the approximate sizes of each part. Using blocks of scrap foam, raise each part until it is resting where it will eventually be located. For the time being, you can secure it in place using some duct tape, if you wish.

  3. 3

    Following your drawings precisely, use a heavy marker to draw out the details directly onto the foam. Make note of the depth each indentation or cutout should be carved to. Draw half of each body panel first, then carefully measure and copy each design detail to the opposite side to ensure perfect symmetry. All it takes is one mistake to completely ruin the project, so triple check your measurements before work begins.

  4. 4

    Begin carving your design into the foam, being careful not to damage the parts during this process. When you lay the fibreglass on top of the foam, remember that each of the parts will be slightly thicker, so compensate for that during your cutting. Make sure every single cut lines up with the marks you drew in the previous step. If you make a mistake, you don't have to scrap the entire piece, just cut out the ruined section, glue another block of foam in its place, and resume work.

  5. 5

    Remove the finished foam pieces, and cover them tightly in aluminium foil to prevent the resin from sticking. You may want to use an adhesive spray to hold the aluminium into place on the foam. Next, spray the outside of the foil with a non-stick cooking spray, which will act as a mould release when you remove the fibreglass. The parts are now fully prepped.

  6. 6

    Begin laying your fibreglass. Start off with just one sheet soaked in resin, and lay it across the outside of the mould. Use a roller to push out any air bubbles, and tuck the fibreglass sheet around the edges and contours of your body kit. Allow the single sheet of fibreglass to completely dry, then gently pull it off of the foam mould. Be careful, as the single fibreglass sheet will be very fragile.

  7. 7

    Reinforce the inside of the parts using multiple layers of thick fibreglass matting. Smooth out the air bubbles on each layer, and allow adequate dry time before moving on to the next layer of glass. By placing this matting on the inside of the parts, you can add as much thickness as desired without changing the outside shape of the finished product.

  8. 8

    Sand the outside of the parts using a rough grit sandpaper, to smooth out any bumpy areas or lumps. A metal file can be used around the openings to ensure clean edges. Use a proper breathing respirator, thick gloves, and long sleeves to protect yourself. Once the finished look is achieved, blast the parts with an air compressor to remove sanding dust, then wipe the entire surface down to remove the last bits. Now is a great time to do a test fit to make sure the parts line up to your satisfaction.

  9. 9

    Cover the entire outside surface with Bondo to create a smooth, finished texture much like a worked piece of auto body sheet metal. Multiple layers may be necessary to thoroughly cover the surface. After letting it cure, sand the Bondo to a flat surface, but don't leave it perfectly smooth. You want to finish with a somewhat rough sandpaper to make sure the paint sticks. Wipe the finished product with isopropyl alcohol to prep it for the next step.

  10. 10

    Prime the parts for paint. Any commercial automotive primer in a spray can will work fine. Use long, sweeping motions to cover the entire surface. Start spraying the can before it hits the surface, and do not stop spraying until you have completed the sweep, and have cleared the surface on the other side. This ensures uninterrupted coverage. Two coats of primer is plenty, and it only needs to dry five to 10 minutes between coats. Let the final coat cure for a couple of hours before moving on to paint.

  11. 11

    Paint your body kit. Use the same, long sweeping motions to completely cover the surface. Use multiple coats of very light paint, as opposed to thicker coats. Same with the primer, let it cure for five to 10 minutes between coats, then move on to the next one. It may take 10 or more coats to thoroughly cover the surface. When done, top it off with two coats of clear coat to protect the finish.

  12. 12

    Mount the body kit to your car. You can use the same mounting system that the original bumpers and trim pieces used, though depending on your car, you may have to craft some custom brackets to do so. Double-check clearances to make sure the panels are tight and everything looks like a good fit.

Tips and warnings

  • As an alternative, you can cover the foam pieces with plaster, then use the resulting mould to make perfectly formed fibreglass parts that are the exact same thickness as the foam mock-ups.
  • You can make ground effects by adding thinner body kits to the bottom of your existing bumpers, giving the car a lower, sleeker look.
  • Never wax fresh paint. It takes 60 to 90 days for the paint to fully cure. In the meantime, protect it with an automotive glaze.
  • Always use a safety mask when sanding fibreglass.
  • Be careful to avoid fibreglass splinters when handling the parts.
  • If you don't securely attach the body kit to your car, you risk it falling off on the highway.

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