Epoxy vs. Polyester resin

Hello all,
Another question, what are the pro’s and con’s, yes I know polyester is smellier but? I saw on the Duck soup web site that there is a mixed back of stuff used to build hulls both poly and epoxy.

Here is my new cedar hull and my other two boats, on balsa core, one just three layers of glass.

Once upon a time, polyester resin was thought to be waterproof. Ask any of the thousands & thousands of boat owners that have a bottom damaged by osmotic blisters & they’ll tell you it’s not . Now you’re probably not going to get blisters on your toy boat unless you’re some incredible die-hard in need of an intervention, but using a quality goo never hurts. There are five main resin chemistries commonly used in boat building. The oldest & most often used (in full sized boat production) is orthophthalic polyester resin, it’s the cheapest, easy to use, brittle, has a fairly low tensile strength & hurts your mouth to pronounce. Next in line is isophthalic polyester resin, it has much better mechanical properties than ortho resin, greater tensile strength, over twice the elongation spec, superior secondary bonds and better chemical/osmosis resistance. A third resin is known as DCPD which stands for poly dicyclopentadiene (a word not commonly used is everyday conversation). It has a lower styrene content than iso or ortho resin which helps manufacturers meet strict EPA styrene emission levels. A side benefit of less styrene in the mix is less shrinkage during cure (there’s less styrene to evaporate so the goo shrinks less). Since it shrinks less it’s often used to lay-up the first layer of glass to minimize “print through” of the glass weave into the gelcoat. It’s also has better resistance to osmosis than ortho/ios resins & serves as a sort of half-assed osmotic blister protection. Pure DCPD resin is too brittle for boatbuilding so it is blended with either ortho, iso or vinylester. Vinylester resin is the fourth choice & is handled much the same as polyester resin. It is a much superior goo to polyester as far as fatigue, impact resistance, adherence and osmosis resistance. The absolute KING is EPOXY. It is superior in all properties except price. The price aspect is actually very trivial considering the wee amounts of goo used in a toy boat. Even in a full sized boat the extra cost for epoxy resin versus polyester is a very small percentage of the total cost of the boat. If you want to build the best, use the best. Epoxy resin is not that much more expensive than polyester resin. A gallon of poly is about $28USD, a gallon of 1:1 laminating epoxy is $39USD. Those of you that are using West System products are probably thinking that I have some form of head injury because you paid somewhere around $100USD for a gallon of goo. They might as well change the name to “The Goudging Brothers”. Don’t get me wrong, West System products are very good, they’re just way overpriced. If you would like to not take out a second mortgage for epoxy, give Fiberglass Coatings Inc. a try. <<www.fgci.com>> The finest laminating epoxy that they sell for boatbuilding purposes is the 3:1 ratio goo. It is a very high quality product. FGCI has a resident chemist, you can actually talk to him. They make all manner of magical coating goo. The latest epoxy goo chemistry that FGCI is using is DOT non-corrosive so you shouldn’t have to pay for hazardous shipping. I rarely use anything except the 3:1 blend, it’s near $50 per gallon. The 1:1 & 2:1 blends are a little bit cheaper but they don’t have anywhere near the resistance to water absorption. The 3:1 blend is also very chemically resistant. I use this to coat the inside surfaces of metal fuel tanks (after etching them with acid). You’ve got a pretty nice looking hull there, with obviously a fair amount of work involved. Don’t be tempted to save a few bucks by using an inferior goo. If your intent is to finish the hull bright (just a clear coat) you might look into the “Table Top Crystal Clear UV Epoxy” that FGCI offers. I’ve never actually used it so I’m not sure just how suitable it would be for a marine environment. The “UV” part of the name piqued my interest. Normally, epoxy is poor against UV exposure (one of it’s few weaknesses) so it should always be covered with paint or varnish. I feel as though I’ve been rambling, I hope some of this helps.

Happy Yachting - Kip

And that lot is pure, unadulterated common sense, backed up by knowledge!