OK, I have been studying up on fiberglass repair, reading books, posts on the internet, West system manuals, etc. I wanted to understand what I was getting into before I tear into this project boat of mine. Of course there is this debate going on over the use of epoxies or Polyester resins for fiberglass repairs.<br /><br />And I am not here to solve it I just want to provide some information I have gleaned from several sources.<br /><br />In short what I am planning on doing at the current time is to use both products in my repair.. I will seal all of my plywood components; the stringers, decking, and transom in 2 coats of standard marine epoxy.. Then I plan to install these sealed components into my boat with Polyester resins and standard Fiberglass mats and cloths.<br /><br />Here is my reasoning. Epoxy is more waterproof than Polyester. Epoxy will virtually guarantee that water and mold will not get to the plywood. But Epoxy resins are also double the cost of polyester resins. Epoxy is about $50 a gallon: <br /><br /> http://www.clarkcraft.com/cgi-suppl...esin&*******=7f1f5b445920d7593ea7931b9b817d10 <br /><br /> http://www.shopmaninc.com/epoxy.html <br /><br />Polyester is about approximately $20 a gallon: http://www.shopmaninc.com/polyesters.html <br /><br />Polyester is also designed to go along with ALL types of fiberglass cloth, especially Matting because the polyester can dissolve the binders in the matting, which Epoxy can not. And I know there are special Epoxy matting materials, if you want to pay $$$ for them..<br /><br />I especially want to use matting when I am laminating up the transom on my boat. Currently my 14 foot fiberglass runabout has 2 layers of ¾ inch plywood that are totally delaminated and dry rotted. Fortunately, I can get to and remove the entire transom from the inside of the boat without splitting the deck ,etc Hopefully.<br /><br />So my plan is to replace the transom with 3 layers of 3/8 ply and matting in between each layer. In order to get these pieces into place I am going to have to cut them in different places and then laminate them back together in the boat..<br /><br />From the outer skin, I plan to lay in:<br />Matting w/polyester resin<br />Epoxy sealed 3/8 inch Plywood (Cut horizontally to get it into place)<br />Matting w/polyester<br />Epoxy sealed 3/8 inch Plywood (Cut vertically)<br />Matting w/polyester<br />Epoxy sealed 3/8 inch Plywood (Cut to fit with add-on Blocks)<br />Matting w/polyester<br />2 Layers of roving / cloth with Polyester resin to finish the job.<br /><br />In reading Allan Vaitses book, The Fiberglass boat repair manual he makes an interesting observation in Chapter 3 on page 56 that Polyester resin and fiberglass DO NOT stick well to wood; Wood shrinks and swells as its moisture content changes and glass that is laid up on it does not (shrink and swell); they therefore simply wont stick together through many shrinking and swelling cycles He even goes on to say that polyester should be MECHANCIALLY fastened to wood instead of expecting it to glue itself to the wood.<br /><br />Here is a PDF of the pertinent pages so you can read and let me know if I drawing the wrong conclusion from this. http://mysite.verizon.net/sdunt/boat/Tabbing Parts to Fiberglass.pdf <br /><br />That would tend to lead to the conclusion that only Epoxy should be used around wood because of its adhesive properties. But I also found an article from the West Systems Epoxy Works magazine with test data that indicates that Polyester Resin, in this case Gelcoat will stick to Epoxy very well: <br /><br /> http://www.epoxyworks.com/22/polyester.html (The entire Article Here are the interesting parts)<br /><br />Conclusion <br />The overall effect of moisture on the gelcoat's bond to both the polyester and epoxy panels was negligible. The graphs show very little change in the adhesive strength, and much of the variance is within the tolerance of the test method. When the studs were pulled, the failures occurred in the fairing compound, cohesive failure of the gelcoat, or in the bond between the gelcoat and laminate. Since these three modes of failure occurred under similar loads, it indicates that the strength of the bond is close to the cohesive strength of both the gelcoat and the fairing compound. The nine-week exposure may not simulate what could happen after many years, but it does indicate that the gelcoat bond to epoxy laminates is a good bond and should perform well. <br />Our test clearly demonstrates that polyester gelcoat will bond to a properly prepared WEST SYSTEM® epoxy as well as to a cured polyester laminate. This test confirms that polyester gelcoats can be applied over cured WEST SYSTEM epoxy on repairs below the waterline. <br /><br />So I am taking all of this together to say that I should use Epoxy to seal the wood and that will stop the moisture changes and the shrink / swell cycle, also epoxy will actually soak into and glue itself to the wood. Then because Polyester Resin will stick to the epoxy, its cheaper, it works with all kinds of mattings and cloths, and it sticks well to the original fiberglass, I can use it to assemble and finish the repairs.<br /><br />Can someone in the repair business read this over and let me know if I am nuts. Keep in mind that this is a on the cheap repair. I only have $100 in the boat, the outboard and the trailer..<br /><br />Thanks..
