How to make a fiberglass tank mold

Updated March 23, 2017

Fibreglass gas tanks are a popular option for motorcycle and off-road vehicle enthusiasts looking to customise their machine. These tanks are often weigh much less than a traditional metal gas tank, which can be valuable for riders looking to maximise fuel efficiency. They are also considered a safer alternative to metal tanks for extreme sport racing, and other riding situations where an impact is more likely to occur. Due to the way in which fibreglass shatters and responds to impact these tanks can provide a wealth of safety benefits compared to metal tanks. Making your own fibreglass tank should take two to three days.

Determine the size of the gas tank you will be creating a mould for using your measuring tape. In most cases the simplest way to attain these measurements is to use an existing compatible gas tank.

Purchase blocks of floral arrangement foam from a craft store. This foam is usually dark green, and can be bought in a variety of different shapes and sizes. The foam will be used to carve out a mould of your gas tank, so you may need to purchase multiple blocks of foam to cover the size of the tank.

Use spray adhesive to connect multiple blocks of floral foam together. Allow the adhesive to dry before cutting.

Sculpt the foam using a carving or modelling knife. Start from the bottom and work your way up, using your measuring tape to ensure proper dimensions. It may be helpful to have your gas tank or motorcycle nearby for visual reference as you sculpt.

Stop sculpting occasionally to ensure symmetry on both sides of the foam. Use your knife to pare down uneven edges, measuring each side with the measuring tape for precision.

Use low-grit sand paper (grade 220 to 400) to sand down the foam and finalise your mould design.

Coat the interior of the mould with a liberal coating of mould-release wax. This wax will ensure that the fibreglass does not stick to the mould as it cures.

Cut your fibreglass cloth to the necessary shape and dimensions using scissors.

Mix your epoxy resin in a small container, stir the resin thoroughly to attain an even consistency.

Coat the interior of the mould with resin, use a paint brush to ensure that it is evenly distributed.

Apply the fibreglass cloth over the resin. Apply pressure to the cloth as you lay it to avoid folds or wrinkles in the cloth.

Coat the exterior layer of fibreglass cloth with resin, then lay a second layer of fibreglass cloth on top. Run your paint brush along the fibreglass cloth to evenly distribute it. Use a putty knife to remove air bubbles as they arise. Continue layering epoxy and fibreglass until you have four layers of fibreglass cloth.

Allow the entire mould to set for at least 24 hours. Once the fibreglass and epoxy have completely set, remove the fibreglass from the mould. Sand the cured fibreglass until you can expose the seam where the fibreglass meets the edge of the mould. You can use a tongue stick to pry at this seam if the fibreglass sticks to the mould.

Use sandpaper to sand the exterior of the fibreglass and remove any blemishes or imperfections.

Things You'll Need

  • Measuring tape
  • Floral arrangement foam
  • Spray adhesive
  • Knife
  • Low-grit sandpaper
  • Mold-release wax
  • Fibreglass cloth
  • Epoxy resin
  • Scissors
  • Container
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About the Author

Jacob Stover is a writer and editor from Ann Arbor. He has been writing professionally since 2009. His work has been published in the "Wayne State University Literary Review." He holds a Bachelor of Arts in English and film studies from Wayne State University.