How to Repair a Longboard Fin Box With Epoxy Resin

Written by sean chappell
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How to Repair a Longboard Fin Box With Epoxy Resin
Fixing your board on you own will get you back in the water faster than going to a surf shop for repairs. (longboard image by bacalao from

The fin box is a square plastic piece that is glassed into the bottom of the board and is used to hold the fin in place. If you've had a recent encounter with shallow rocks while riding a wave, it's possible that you caused damage to the fin set-up on your longboard. No one wants to miss out on good waves while waiting on a shaper to repair a damaged longboard. If you have a damaged fin box, you can perform the repair on your own and get back in the water within a few days.

Skill level:

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Things you need

  • Epoxy resin
  • Fibreglass cloth
  • catalyst
  • Plastic cup
  • Craft stick
  • Sand paper
  • Block sander
  • Masking tape
  • Coping saw

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  1. 1

    Use a razor blade to cut around and remove the fin box. If the fin box is cracked, throw it away and buy a new one at your local surf shop. Turn your board upside down and allow it to dry out for 24 hours; any remaining water will permanently damage your board.

  2. 2

    Prepare your board to be repaired. Use a razor blade to away any soft or damaged foam around the fin box, leaving the surrounding area with dry and firm foam. Cut out a piece of new foam using a coping saw to fill the damaged area. Shape as needed by sanding or cutting with a razor blade. The piece should wrap around the fin box and fit snugly into place.

  3. 3

    Use a craft stick to mix 56.7 to 113gr. of epoxy resin in a plastic cup and add several drops of catalyst.

  4. 4

    Pour enough resin to cover the area where the fin box will be set. Place the fin box into the slot where it was set originally, and add more resin to attach the foam piece that you cut out before. Press down firmly so there is no air between the foam and make sure the fin box is set level. Allow to dry overnight in a well-ventilated area (e.g., a garage with the door cracked open).

  5. 5

    Use a block sander to smooth out the surface of the bottom of the board and the area surrounding the fin box. Cut out a piece of fibreglass cloth to fit around the unfinished area around the fin box. Cover the slot in the fin box with a piece of masking tape to prevent resin from leaking in and hardening.

  6. 6

    Mix epoxy resin in a cup with catalyst. Use a craft stick to put a layer of resin on the board surrounding the fin box. Lay the fibreglass cloth on around the fin box and put one last layer of resin on top. Make sure the final layer slightly overlaps the edges of the fin box. Allow to dry overnight and sand to a clean, smooth finish using a block sander.

Tips and warnings

  • If the fin box is wobbly, it can be removed and reset. If the fin box is cracked, it needs to be removed and replaced.
  • Do not add the catalyst to the epoxy until you are ready to apply it. Catalyst is a chemical reactant that causes the resin to harden after about 10 to 20 minutes of use.
  • Work in a well-ventilated area. Do not work inside your house; the smell is very strong and can cause nauseousness.
  • Use a mask and gloves when handling resin. Resin is toxic and extremely messy and difficult to clean up if it gets on your skin.

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