Q&A Epoxy Resin vs Polyester Resin for Wood

Should one fibreglass using epoxy or polyester resin over wood.

In this case it was to join the plywood panels of a stitch and glue boat.

First, Woven fabric will give a smoother finish than chopped strand matt and is much stronger for the same weight.  It also requires less filling of the weave to get a smooth surface.

epoxy glass taping boat chine: storerboatplans.com

If you want the boat to last a long time I would be using epoxy rather than polyester.

The polyester relies on going a little way up the cellulose tubes and hardens. Just sort of tangles up.

The epoxy tangles up the same way but ALSO joins onto the molecular structure – much stronger.  It actually joins onto the molecular structure of the cellulose (hydroxyl bond) which polyester doesn’t.

One of the sad moments in my boat repairing life was after I had used polyester resin to fibreglass a boat’s deck.  The owner came down the day after the ‘glass had been resined and said it looked nice.  He then noticed a thread hanging out the edge and gave it an unconscious pull.  Half a metre of the cured surface tore off.  Back to the drawing board!

Epoxy IS more expensive but does a much more permanent job. But if you just want the boat for a couple of years and then are happy to throw it away polyester will probably be OK and will save you money.

Sometimes polyester does stick OK to wood, but it is not reliable.

For information see our FAQ on how to use epoxy. Here are some sample articles.

Preventing Rot Pt 1 – The Good, the Bad and the Fugly
Preventing Rot Pt 2 – Epoxies that “soak in”
Eliminating Screws and other Fasteners – save money and do a better job

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