: Don't mean to open a can-o-worms but I gotta ask.....why epoxy instead of the
: much cheaper poly resin? I have built four s&g kayaks using top dollar
: epoxy and think I might try using the poy resin for my next project.
: Doesn't make sense that nearly all production boats are made using poly
: resin not epoxy, but yet most home builders all use the high dollar epoxy.
: comments.........

We go over this every once in a while.

There are good explanations of the strengths and weaknesses of these materials at varius sites, and in several books. You can do extensive research and come up with numerous answers to this question. But basically it boils down to picking one or the other -- and most people are now picking epoxy.

It was not always this way. Many boats were built with polyester resin, and many are still being made with this material. If you get a "fiberglass" boat the odds are that this boat was made with polyester resin. However, if you get a wood boat that is covered with glass cloth and a plastic resin, then you are dealing with a different animal.

Polyester resin adheres fine to many types of wood, but some species are too resinous, too oily, or have other problems with polyester resin. Unfortunately red cedar is one of the iffy species for polyester. On the other hand, White cedar is OK with polyester, and for many years the specified materials for cedar strip canoes were white cedar strips and polyester resin.

The greater availability of western RED cedar, particularly in long lengths, and its reasonable cost, led to people building with this wood, and covering the woodwork with the more expensive epoxy resin. Some people continued to use polyester, but sealed the wood with shellac or lacquer before applying the glass and resin.

It is a tradeoff on costs and convenience of the wood versus the cost and convenience of the resin. The glass fabric is frequently the same these days, though in the past some cloth was treated for use with one resin or the other.

You can find many books on building plywood boats in a stitch and glue method using polyester resin and fiberglass tape. H. H. "Dynamite" Payson is sometimes credited with inventing the process. I'm not sure that is completely true, but he certainly has written enough about this to be genuinely credited with popularizing the method. The technique was simply expanded to epoxy resin at a later date.

Polyester resin has some solvents in it which keep it thin. These, and the catalyst that causes it to harden, are nasty materials which can make you ill. Epoxy is somewhat less smelly and somewhat safer, although people do report allergies to the epoxy.

If you want to use polyester resin you will join a long line of people who have done so, and you will probably be very happy with your boat.

It will probably cost you less and you may finish a bit faster. Take care to wear a good respirator mask (you can easily afford one with what you save on the costrof the resins). if you are careful with the applicaton of the resin you may have fewer runs (polyester is a bit better on vertical areas as it is thicker) and you may be able to skip sanding between coats of resin as you fill the weave of the fabric (in the presence of air the polyester hardens with a tacky surface that accepts the next coat of resin readily. Your last coat must block air from the hardening resin). Unlike epoxy boats you do not need to varnish this to protect it from UV radiation, so you'll save time and money.

With all the good things going for polyester there are a few better things going for epoxy:. It flexes better so it stays in better contact with the wood should you hit rocks, or be in situations where the boat is stressed a great deal. This means fewer areas of delamination to be fixed over the years. It is easier to mix small batches. It is a superior glue, so joints are somewhat stronger. (Polyester is strong and well proven; epoxy is stronger. But how strong is strong enough?) Epoxy also soaks into the pores of the wood sealing it (or encapsulating it) to prevent water absorption. This factor alone is highly desired for wood products used in a marine environment.

hope this helps

PGJ