How to Make Your Own Fiberglass Mold

Written by quyen tong
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How to Make Your Own Fiberglass Mold
You can make your own fibreglass mould at home. (Hemera Technologies/ Images)

You can save money by knowing how to make your own fibreglass moulds. Working with fibreglass allows you to make car body parts, boat parts and various home decorations. Creating a fibreglass mould can be tedious work. Even so, it is a beneficial skill because it allows you to control the quality of your project.

Skill level:
Moderately Challenging

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Things you need

  • Styrofoam
  • Bondo
  • 180-grit sandpaper
  • 220-grit sandpaper
  • Polyester primer
  • Moulding wax
  • Resin
  • Polyester resin and hardener
  • Plastic mixing cups
  • Brushes
  • Fibreglass roller
  • Fibreglass mat
  • Razor blade
  • Wooden mixing stick

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    How to Create the Mold

  1. 1

    Carve the foam block according to the specifications of your design. If your project is too large for one foam block, you can glue multiple pieces together. Sand the foam with 180-grit sandpaper to remove rough edges and unwanted undulations.

  2. 2

    Cover the foam with Bondo and allow it to dry for two hours. Sand the Bondo with 220-grit sandpaper until smooth. Spray the polyester primer directly on top of the Bondo in three even coats and allow it to dry. Drying times will vary due to different manufacturers, so follow the directions on the label carefully.

  3. 3

    Once dry, sand the primer with 220-grit sandpaper and continue to sand with finer grits. You can stop the sanding process once you are wet-sanding with 1,000-grit sandpaper. To wet sand, mist the surface with water and use 1,000-grit sandpaper to sand the surface until it is completely smooth.

  4. 4

    Allow your mould to sit for three or four days, waxing it once a day. Wax the mould just as if you were waxing a car. Apply the wax and allow for it to appear foggy. Once foggy, buff off the wax until the mould is shiny.

    How to Lay Fiberglass

  1. 1

    Cover the mould in tooling gel and allow it to get tacky. Once tacky, brush the resin directly on top of the moulding gel. Separate the fibreglass sheet into fine strands and place it on top of the resin. Use a roller to remove any air bubbles stuck in the resin. For a thicker piece of fibreglass, you can lay more layers of resin.

  2. 2

    Cut the protruding pieces of fibreglass with a razor once the resin has dried. Remove the fibreglass part with a wooden mixing stick.

  3. 3

    Paint directly on top of the fibreglass or sand the surface before painting. Do not sand too much of the raw fibreglass surface or you will reveal the fibreglass strands behind the resin. To obtain the smoothest surface, wet-sand with 1,000-grit sandpaper before and after painting.

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