How to Use Fiberglass Filler


Fiberglass filler is a thick putty-like substance made from fiberglass resin and a number of cheap substances that thicken the resin. Fillers main ingredient is resin, so it needs a catalyst to cure or become hard. This can be used on anything from repairing a leaky hot tub to repairing a chip in the hull of a boat. Also filler is used for bodywork on cars and other metal needs. Filler is basically used just like bondo for filling in small holes, chips, or cracks.

Things You'll Need

  • Sandpaper
  • Rags
  • Respirator
  • Rubber gloves
  • Putty knife
  • Fiberglass filler
  • Hardener
  • Small bucket
  • Stir stick
  • Prepare the area you're applying the filler too by scuffing it with 100-grit sand paper. Make sure no shiny spots are left on the surface.

  • Wipe the area with a damp rag to remove any remaining dust. Make sure the area is dry before you apply the filler.

  • Wear rubber gloves when you mix the filler and hardener together as directed on the containers. This can take a couple minutes to thoroughly mix. When the mixture is all one color, it is ready to apply.

  • Use a putty knife to apply the mixture until the gap is entirely filled. Smooth the filler out so it is level with the surrounding area. Make sure the filler is flat and smooth to save some sanding time. Let it cure until it's hard and cool to the touch.

  • Wear your respirator as you sand the area until you have a smooth and level surface.

Tips & Warnings

  • Always wear a respirator and saftey glasses when you work with fiberglass.


  • Photo Credit tmib seattle/
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