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How to Apply Fiberglass to Wood

by Richard Rowe

Wood and fiberglass seem like something of a perfect match. Fiberglass resin is designed to soak into a material matrix to strengthen and seal it, be that matrix of glass fiber or plant cellulose. Fiberglass resin can seal wood to form a shell that protects the wood, and provides a smooth painting surface. It also fills in any imperfections. Glassing over wood requires a few precautions and techniques to ensure uniformity, strength and bonding.

Turn the heat in your shop up until the room reaches about 90 degrees, and allow it to maintain that temperature for 20 minutes before beginning the fiberglass procedure. Place the resin in front of your heater vent to bring it up to about 85 to 90 degrees. Heating the room in this way will open the wood pores to prepare them for fiberglass application.

Mix the resin and hardener according to manufacturer recommendations. Do not mix any more than one cup at a time, as the resin/hardener reaction will create its own heat and speed curing. Pour resin into disposable roller tray. Soak the foam-head roller with resin very thoroughly, but roll it out in the pan afterward to remove excess.

Roll the resin-soaked roller directly onto the wood surface to seal it. Use very slow, even, diagonal strokes to apply the resin without causing it to foam up. Cover the entire wood surface, and then open your shop door to quickly vent the hot air. This will cause the wood pores to shrink while the resin sets up, sucking the resin into the wood and preventing bubble-causing "out-gassing" from the wood. Allow the resin to set up completely until it is completely hard.

Sand the entire surface with 120-grit sandpaper to help the next coat of fiberglass stick.

Repeat Steps 1 and 2. Cut your fiberglass mat into six-inch strips and lay them on the surface. Run the resin-soaked roller over the fiberglass mat, soaking it thoroughly but not so much that the resin builds up and runs. You might be tempted to simply pour the resin over the mat and spread it, but do not; the glass mat will float to the top of the resin and show through to the finished surface.

Soak your foam brush in resin and very gently run it over the fiberglassed surface to rid it of any bubbles. Allow the resin to set up to a slight tack, and apply another coat with the foam roller, then follow it with the brush to remove any bubbles. Allow the fiberglass to harden fully -- at least two hours to ensure that it is completely set.

Sand the surface with 500-grit sandpaper, and then 1000-grit sandpaper. Wet-sand the finished resin with 1000-grit sandpaper to leave a beautiful, transparent surface that will bring out the grain of the wood and keep it from harm.

Warning

  • If you are planning to fiberglass an old wooden boat to restore it, bear in mind that the fiberglass resin will seal into the wood any moisture, bacteria or mold it contains. These things will eventually cause the wood to rot inside the fiberglass shell, leaving it visually acceptable but structurally unsound.

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About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

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