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Epoxy runs

Discussion in 'Strippers, Stitch-n-Glue, and Other Wood Composite' started by Bradh, Sep 3, 2008.

  1. Bradh

    Bradh New Member

    I'm a first time strip canoe builder and have been successful so far build a staplless canoe. But now, after all my work I've messed up on my epoxy. I'm using Raka non blush and wetted the wood before applying the glass. When I was wetting the glass the next day it was a little cooler than normal, high 60's in the shade. I think I applied the epoxy too thick and by the time I was done I realized I had significant runs. I didn't notice them until the sun got low enough to shine into my garage but Oh My God, it's not pretty. I waited another day, lightly sanded and added another coat to fill the weave and hoped that the runs would disappear. They haven't. Can I sand them out, scrape them? What's the best method and is this common?
     
  2. Dan Lindberg

    Dan Lindberg Ex Wood Hoarder

    Epoxy runs - yes, they are common when too much resin is applied, (or not scraped off). Espeshilly if you are using the same resin to fill the weave as you did to wet it out, roll on thin coats and use a plastic wide blade "knife" (think drywall) to smooth the wet resin surface. And let the resin flow out.

    Yes, the best method to remove them is to use a carbide paint scrapper after they are cured.

    As for the "look" of the curing resin. It doesn't matter, as you need/should be block sanding it "flat"/smooth anyway prior, to appling 2-4 coats of uv resistant marine varnish. The varnish should also be sanded between coats.

    When you are finished, if you look at it with reflected light, it should be flawless. Check out some of Martin Step's pics for examples, at Green Valley.

    Dan
     
  3. Todd Bradshaw

    Todd Bradshaw Sailmaker

    I don't know where you are getting your instruction from, but I think the only problem you have is one of perception of the directions and/or methods for building a stripper. Epoxy resin is not varnish, and it doesn't behave and self-level like varnish. Nobody (and I mean NOBODY) can roll, squeegee or brush epoxy filler coats on a canoe and wind-up with a suitably smooth surface ready to show the world. You fill until you have completely covered the cloth texture and then sand or scrape it until it's truly smooth, followed by varnishing. Trying to fill so neatly with epoxy that there is no need for final smoothing is both impossible and the true mark of an amateur building job.

    Drips in filler coats don't really matter because they will be removed as part of the process (or at least they should be if your goal is to build a good boat). It may take a few additional seconds with a sander or scraper to remove a hardened drip than it would have to prep a smooth spot, but that is the only penalty you pay for having drips. When I fill I totally ignore drips and don't waste any time at all worrying about them during the filling process. They will be removed later with no problem as a normal part of the finishing process and the hull will end up as smooth as a baby's butt.

    There are, however, some things that ARE very important in the process. Getting the cloth down tight on the surface, careful roller and squeegee work to avoid introducing a lot of tiny bubbles in the cloth and being sure that you have adequate thickness of filler coats in order to be able to do your final smoothing without cutting into the cloth. The dumbest thing in strip building are directions that specify how many filler coats you should add to hide the weave.

    This is one of my pet peeves and every single strip builder should understand it. Different brands of epoxy resin and different specific formulas within those brands have different viscosities - some are thicker and more syruppy, others tend to be a bit thinner. As temperature varies (both workshop temp and the temperature of the resin itself at various points during the application) the viscosity of the resin also varies. It will actually even be changing as you are applying it. Different application tools and different builder's application techniques also vary considerably. The end result of all this is that nobody can tell you ahead of time how many filler coats you will need. You make that decision as you work. The safest rule of thumb to get the weave covered and give yourself a little cushion to allow you to sand later without cutting into the fiberglass cloth is actually quite simple:

    "Add filler coats as needed until the weave it totally covered and not visible anywhere - - and then add one more filler coat."

    Depending on the conditions, the particular resin and your application style, this might take three or four coats, but it might also take six. The important thing is not how many coats it takes, but how well the cloth is covered when your done. The final resin thickness should be the same either way, it's just a matter of what it takes to get there. Once cured, you're ready to sand or scrape as needed until the surface is smooth, drip-free and ready to varnish and be proud of. With a $50, 5" random orbit sander you can go from "drip-mania" to professionally smooth and ready for varnish in two or three hours of not particularly difficult work.
     

    Attached Files:

  4. Jim et al

    Jim et al Curious about Wooden Canoes

    Great advice to keep you motivated Brad. I would add change your sandpaper early and often to keep the smoothing going quickly. As soon as I sense the paper disk is no longer cutting as well as it should I swap it out for a new one. It may be a bit wasteful but it really helps reduce sanding time.

    Jim
     
  5. Canoez

    Canoez Paddle Bait

    Runs in Epoxy

    I've found that for cured runs in epoxy, the best solution to get rid of them is to use a cabinet scraper. You'll have to sharpen it fairly often, but it removes just the runs in a fairly quick manner.

    The big plus is that unlike a random orbital sander which operates over a small area and can create digs, divots and unfair surfaces, the cabinet scraper, followed by a flexible longboard gives an excellent surface. I always find people tend to focus on a small area when using the orbital sander and wind up with unfair areas. If you use a random orbital sander, keep moving!!!
     
  6. OP
    OP
    Bradh

    Bradh New Member

    Thanks for your advice. I'll add another coat to cover completely and will scrape or sand to smooth. Picture to follow
     

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