Making fiberglass car molds

Written by james mulroy
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Making fiberglass car molds
Car bodies can be made from fibreglass moulds (modified car image by FotoWorx from

Cars can be made using a number of methods. Traditionally, car parts are machined or cast. However, car parts now are frequently being made out of composite materials. These composite material parts are made by laying up epoxy and a fibre (fibreglass/carbon fibre) onto a mould. The mould can be made out of various materials including wood, metal or fibreglass. Fibreglass is often chosen due to its high strength-to-weight ratio. The DIY person can build their own fibreglass car part moulds by making an exact mould of a pre-existing car.

Skill level:

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Things you need

  • Lab coat
  • Nitrile gloves
  • Safety glasses
  • Poreless peel-ply
  • Car part (bonnet, exhaust pipe, etc.)
  • Fibre-reinforced polymer (FRP) mould release
  • Epoxy
  • Polythene cup
  • Wooden stir rod
  • Fibre (fibreglass)
  • Rotary cutter
  • Epoxy spreader

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  1. 1

    Dress yourself in proper attire including a lab coat, nitrile gloves and safety glasses.

  2. 2

    Lay a sheet of poreless peel-ply down on your working area. Peel-ply is a thin-film plastic that does not adhere to epoxy and will help keep your work area clean.

  3. 3

    Remove the car part that you wish to replicate from the car and place it on the peel-ply.

  4. 4

    Coat the car part in FRP mould release to keep epoxy from sticking to the car part.

  5. 5

    Mix the epoxy to the ratio designated by the manufacturer in the polythene cup with the wooden stir rod.

  6. 6

    Cut the fibreglass using the rotary cutter to the same size of the part that you plan to copy. Cut enough sheets to get your desired thickness.

  7. 7

    Lay a single sheet of fibre down over the car part and spread epoxy over it with the epoxy spreader. The epoxy should saturate every fibre.

  8. 8

    Lay another sheet of fibreglass down and spread more epoxy over the fibre. Repeat this step until you have reached your desired thickness. Allow the epoxy to dry for the time designated by the manufacturer.

  9. 9

    Peel the part from the fibreglass mould and apply FRP mould release to the new mould before laying any composite material down to make a replicate car part.

Tips and warnings

  • Use vacuum bagging to get parts with finer surface finishes and better strength-to-weight ratios.
  • Use enough FRP mould release to completely coat the part. A missed spot will have epoxy permanently glued to it.
  • Use nitrile gloves instead of latex. Some people are allergic to latex and latex also falls apart when in contact with certain chemicals used in composites.

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