Tying poly and epoxy repair areas together

Discussion in 'Fiberglass and Composite Boat Building' started by sbklf, Dec 3, 2007.

  1. sbklf
    Joined: Feb 2006
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    Location: Houston,TX

    sbklf Junior Member

    I used epoxy below the deck, up the sides and over the gunnels for structural repairs on my boat. I then used polyester resin on the top side (deck). Now I have to tie the two together (at the deck/side wall intersection). I know that epoxy bonds to poly and not the other way around so I poly'ed the deck to within 3" of the side and plan to epoxy that 3" and then another layer overlapping the poly to tie them together. Will this work?

    How long do I need to wait before applying the epoxy over the poly to get a good mechanical bond?

    I have decided to Gelcote the deck rather than using polyurethane paint. What do I have to do to the epoxy areas to get the Gelcote to adhear to it?

    If I ever, do this again, I will reconsider materials to use. Epoxy sounded like a good idea at the time.
     
  2. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    Epoxy IS a good idea. The deck will be a problem under the polyester resin, as it separates and absorbs water. Why didnt you use all epoxy?
     
  3. the1much
    Joined: Jul 2007
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    Location: maine

    the1much hippie dreams

    the poly will only separate if you didnt lay it up right. how many boats over 20 years old have ya seen with delamination caused by water?,,the cause usually starts out as a crack or hole, and the same will happen with ANY resin that isnt maintained.poly boats have been built for years and are still out there.im no epoxy dude, but the chemical reaction of poly stops after 24 hours,so after the 24 hours there shouldnt be any probs., but im not 100% sure. and you do the same with the epoxy area to get it ready for gel as you do the epoxy, the gel dont care if its poly or if ya messed up and used that heavy epoxy heh ;)
    just the regular sanding and prep'n the area
     
  4. sbklf
    Joined: Feb 2006
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    Location: Houston,TX

    sbklf Junior Member

    Why do you think the deck will be a problem? (it's Nidacore). I went with poly where I could mostly due to cost but I also want to gelcoat the deck because I feel it is more durable than paint. The epoxy area that will show is not that large so I figure if I have to, I can mix paint to match the gelcoat for that small area (I don't mind if the deck is not perfect).

    I layed some epoxy over one week cured poly yesterday. As of this AM it seems to have cured OK and bond.
     
  5. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    My mistake - I made the assumption it was wood because you used epoxy. In that case I wonder you used epoxy on the hull at all- asuming it was Nidacore as well.
    A few more details needed i guess.
    I do know that two pack poly paint will be a darn sight easier to apply and get a good result from than using Gelcote. gelcoat is a thick goo, and laying it out and sanding it smooth is a major time eater.
     
  6. the1much
    Joined: Jul 2007
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    Location: maine

    the1much hippie dreams

    ta get gel ta sand, get the "waxed" then put it on thick, sand with 220 for a few, then 320, then its ready for primer, unless your staying with gel, then ya just add the wet sanding. and if durability is an issue, then awl-grip is more durable then gel,, but then ya cost goes up,,,,,,,ALOT ;)
     
  7. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Sand the polyester resin well before applying epoxy to it and it will last much longer. There will be an unreacted somewhat sticky layer on the surface of the polyester and the epoxy won't bond well to it, so this layer needs to be removed. A week of non use is not a good test of the bond.
     

  8. AroMarine
    Joined: Jul 2005
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    Location: Atlantic City NJ

    AroMarine Junior Member

    First things first when interchanging products polyesters/epoxy the most important thing is making sure your underlying work is cured. Depending on the size of your repair a heat gun is a good choice. Curing both the polyester and the epoxy using your hand as temp guage serves me well: If it is too hot for your hand it is too hot for the resin. When the polyester is cured grinding is better than sanding for your epoxy tab. 36 grit. Do not wipe down with solvents ie. acetone/lacquer thinner. Use water instead. Also vacuuming with brush is much better than blowing the work with air. Applying gelcoat to epoxy is possible. I have had better luck with West System for this using fast hardener even in a warmer climate. MAS resin a little less better also using fast hardeners. 50/50 epoxy systems have never been good for me using gel for top coat. The important thing is accurate ratios and thorough mixing. Then after overnight cure, minimal time longer is better, using water and scotch brite pads scrub off amine blush from epoxy. Grind or sand depending on you level of cosmetic need then again with water scub work down. Then while wet I heat areas drying the surface and repeat water scrub this helps final cure and cleans amine . Again for final wipe down no solvents use water. Apply gel and your good to go
     
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