How to Fix a Fiberglass Boat Core

The flotation material that makes up the core of a fiberglass boat can be damaged by water, if water gains access to it through the boat's fiberglass skin. Water will destroy the bond between the core and the fiberglass, causing the core and skin to separate, or "delaminate." When you find the soft spots characteristic of delamination, repairs are needed as quickly as possible.

Things You'll Need

  • Drill
  • 1/4-inch bit
  • Marine epoxy
  • Disposable syringe
  • Plastic drop cloth
  • Dock locker
  • 320-grit sandpaper
  • Palm sander
  • Automotive paste wax
  • Electric buffer
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Instructions

    • 1

      Press the fiberglass firmly, running your hand over the spot where you suspect the fiberglass and core to have separated. A firm hull is good; where the hull has a soft spot, the deck has delaminated. Feel around the soft spot and define the area that requires repair.

    • 2

      Drill air holes in the fiberglass soft spot, measuring about 1/4 inch in diameter and spaced about 1 inch apart, using a drill and 1/4-inch bit. The holes must penetrate the skin and go about one-third of the way through the core.

    • 3

      Mix marine epoxy until it's about the consistency of mustard. Pour the epoxy into a disposable syringe. Inject the epoxy into the air holes. Push on the fiberglass as you do so to work the epoxy through the area between the fiberglass and the core.

    • 4

      When the soft spot is saturated with marine epoxy, step away from the work. Lay a sheet of clear plastic, such as a disposable drop cloth, over the area. Move a substantial weight with a flat bottom, such as a dock locker, onto the plastic. Allow the epoxy to cure fully.

    • 5

      Sand the finished repair with 320-grit sandpaper and a palm sander. Paint the repair, if desired. Wax the finished repair with automotive paste wax. Buff with an electric sander.