How to cure fiberglass

Written by c.l. rease
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How to cure fiberglass
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Setting fibreglass requires the use of a resin. Cured polyester resin hardens fibreglass cloth, forming a rigid part. The resin itself will not cure unless mixed with a catalyst called a hardener. Adding too much hardener to the resin will cause the resin to cure nearly instantly. Adding too little hardener to the resin will cause the resin to remain tacky. Fibreglass that remains tacky can sometimes harden with an additional step.

Skill level:

Things you need

  • Fibreglass cloth
  • Fibreglass mould
  • Scissors
  • Polyester resin
  • Stainless steel measuring cup
  • Methyl Ethyl Ketone Peroxide (MEKP hardener)
  • Stir stick
  • Paintbrush
  • Heat lamp

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  1. 1

    Cut multiple pieces of fibreglass cloth to fit inside of a fibreglass mould with a pair of scissors. Set the cut pieces aside.

  2. 2

    Pour enough polyester resin into a stainless steel measuring cup to coat the cut pieces of fibreglass cloth.

  3. 3

    Add the amount of MEKP hardener recommended on the hardener can to the measured resin. Mix the two parts thoroughly with a stir stick. Set the fibreglass cloth into the fibreglass mould. Coat each piece of fibreglass cloth with the mixed resin.

  4. 4

    Allow the coated fibreglass to cure for three to eight hours. The cure time varies depending on air temperature. Temperatures warmer than 21.1 degrees Celsius cause the resin to cure quickly, while cooler temperatures cause the resin to cure more slowly.

  5. 5

    Touch the fibreglass with a finger. Allow the fibreglass to cure longer if it remains tacky. Set the fibreglass under a heat lamp to cure the fibreglass if it remains tacky after 12 to 24 hours.

Tips and warnings

  • Wear protective gloves and protective eyeware when working with polyester resin.

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