epoxy question,

Discussion in 'Boatbuilding' started by zember311, May 31, 2004.

  1. zember311
    Joined: May 2004
    Posts: 16
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    Location: FL

    zember311 Junior Member

    Hello all, first time member of this site.

    I have a question.

    I have been building Radio controlled boats for 12 years, I discovered i am boatstruck and started o build the real deal.

    currently I am working on 2 hydro runners and i just finished a 12 foot by 40" row boat for a friend.

    long story short.

    I am using 635 thin epoxy, 3:1 with 7 1/2 oz, E style fiber glass cloth to cover my hydro.

    there are a few seams, due to the compelxity of the sponsons/hull which left me unable to glass the hull with a solid sheet.

    i found standard 100 grit sand paper cloggs fast when sanding these seams, I went over to the 1/8 grated 120 grit drywall sandpaper and duye to the 1/8 open square grids, the paper lasts a bit longer, but still i am seekign the ULTIMATE SMOOTH finish.

    i used a very dense foam roller on the hull of the row baot and the surface came out great, but the hydro may have some seams that shows through.

    before I try thisd , I thought I would ask,,

    will bondo stick well enough to scuffed 635 thin epoxy to finish out the seams to a smooth surface before my final epoxy coats?

    I am using pigment dye in the epoxy so the pink of the bondo isn't a concern.,

    I'm just not sure if I can do this or not?


  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Epoxy is easier to work when you catch it at stages you can do the most damage. Those seams would have been a bunch easier if you'd have razored through them during the "gel" stage, as they then could be laid flat against the work, rather then over top of each other.

    Since you've now got cured cloth set in goo, you have to abate the surface. I use 60 to 80 grit for the rough in work, 60 on air drive tools and 80 by hand.

    Since this sounds to be a sheathing for abrasion resistance more then hull strength, the method I mentioned above would have been the way to go as you'd only needed fill the weave with more goo to finish off the skinning. Now you got humps. No biggie, grind them down (yea, I know . . . .) and add filler as needed, but only as needed. Bondo can work on boats without engines, but I don't recommend it. It's designed for automotive body work and doesn't take to the vibration created in a powered craft. It will crack and fall off a hull in pretty short order, because they flex a lot more then the stuff is designed for. A better putty would be epoxy and a filler. You get the great bond between the epoxies and the "fairing" process can be controlled better.

    There are a bunch of different fillers available. You'll be using "fairing" fillers and these are light weight, easily sandable materials that are used for cosmetic or surface applications like shaping, filling or fairing.

    West System 407 or 410 are very good fillers for these needs. 407 is a mixture of microballons and fibers (I think) and can be used in bonding applications as it has some strength. 410 is a pure low density filler that is only used for filling/fairing, it sand very easily, though shouldn't be used under dark paint, or other surfaces subject to high temperatures.

    I almost always add other fillers to the filler I need for the job, usually West 406 because I like the adhesive qualities gained by doing so. It increases it's strength and adhesion, but does make it a touch harder to sand.

    Log on to West Systems web site and have them mail you a User's Guide and Manual. They are still free (I think, again) and they have a host of other info available, a lot of it free for the asking, download or mailing. They have a bunch of info available on line about the different processes and techniques too, their book on boatbuilding is worth the cost. If you're really getting into building boats this way then get the book. The web site will be worth the trip there, trust me . . .
  3. zember311
    Joined: May 2004
    Posts: 16
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    Location: FL

    zember311 Junior Member

    Great information~!

    Thank you.

    The razor blade trick is the way I am going to go for future building. That makes the most sense/ not to mention ease in the long run.

    You can see the great luck I had with the row boat @


    That was a custoim hull, no plans, or prints. I ended up with no raised seams on that hull.

    but this one,.


    when it got to the glassing part, I was just a little blown away with folds, cuts, seams.

    I'll get some 60 and 80 action going on, grind the seams down as smooth as i can without going through the glass fabric,( a nice long taper effect ) then a few rolled on final coats should do the trick.

    Thanks again.

  4. lprimina
    Joined: Jan 2004
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    Location: Morehead City NC

    lprimina Senior Member

    Also use bidirectional cloth.
    West system is a very fine company and their products work but there are other companies that have the same type of products at a cheaper price.
    On an earlier thread the home pages of a lot of the epoxy Co. are listed.
  5. Armada
    Joined: Mar 2005
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    Location: Turkey

    Armada Junior Member


    "On an earlier thread the home pages of a lot of the epoxy Co. are listed."
    Could you please advise the lead because I need that lead for my project :)

  6. DavidJ
    Joined: Jun 2004
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    Location: Canada

    DavidJ Senior Member

    I realize this is an older post but there is a couple of issues that concern me. Par is correct about Bondo not being a good choice as a filler; however, I want to add that all polyester products(of which bondo is one) will not properly bond to epoxy. You can use epoxy over polyester, but never the other way around.

    Also I might be mistaken but it appears that zember is using epoxy as a clearcoat and also with pigment added to make it into a sort of paint. I don't know about the pigmented epoxy, but I would highly recommend coating the clear epoxy in a uv resistant varnish(probably the pigmented one as well). Epoxy will yellow when exposed to ultra-violet light.

    Good luck with your boatbuilding zember. I also got started in this business by building model boats. One day I found out my obsession applied to real boats as well. Got a job in the marine industry, started an apprenticship and next fall Im going back to university to study naval architecture.
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