Boat building: Fairing

Discussion in 'Boat Yard Basics' started by oysterbreath, Nov 7, 2011.

  1. oysterbreath

    oysterbreath Well-Known Member

    OK fellas, some of you have built multiple boats. Maybe you've used different fairing compounds. Which are your favorites and WHY? I've been thinking. People always want an easy sanding fairing compound but wouldn't that also mean it's easily scratched when finished? SO in the long run isn't a fairing compound that is a bear to sand better?
  2. cutrunner

    cutrunner Cert. Yamaha technician

    Imo (and im not a pro) is that filler needs to flex, otherwise it will crack. If its too hard it wont flex. But a soft one is easier to damage, and sand. Its kinda your damned if you do, damned if you dont.. But i could be wrong.

  3. WhiteDog70810

    WhiteDog70810 Mostly Harmless

    I only have a "n" of 1, but I can contribute to this discussion.

    You're only laying down thin layers, so the fairing compound doesn't need to be as tough as the epoxy you use to tie the whole thing together. If you build up edges or lay fillets with it, you would probably have some structural issues, but when used as designed it is plenty tough enough. Once you lay your first layer of glass and you have to pretty up all the wood flour/epoxy boogers left over from fillets without gouging the underlying fabric, you will understand why coating the entire bottom with that stuff is a terrifying thought. I also find it is easier to sand 24 hours after it kicks vs next weekend. It does get a bit harder for a little bit after it kicks.

    Protecting scratchable surfaces is the reason guys coat the bottom with graphite/epoxy. By all reports, you better have the bottom where you want it when you lay that stuff down, because it is a bear to sand.

  4. DuckNut

    DuckNut Brandon, FL

    You should have very little fairing to do. You are building a wood boat and wood sands so much easier than epoxy. So fair your wood. Also, your comment about fairing scratching easy - your wood is softer.

    The easiest sanding mix is phenolic microballoons (mix will be brown/reddish) followed by glass microspheres (white) and the hardest is silica (white). Wood flour is somehwere in the middle and depending on the wood used the color will vary.

    Cut is right. It needs to bond well but also flex to some degree. If you make a mix so hard that won't flex you can end up tearing it off of the intended use. Brett had a post of exactly this after a year of use of the grass slipper.
  5. Brett

    Brett > PRO STAFF <

    I used bonding resin and talc between layers of glass,
    For final fairing: gelcoat and talc/cabosil depending on thickness.

    1) Do most of the fairing while the hull is still wood.
        Much easier to sand wood than epoxy or polyester..
    2) Keep your fiberglass layup neat and clean. The smoother your layup the less you need to fair.
    3) Sand down fiberglass overlaps before applying the next layer of 'glass.
        Those overlaps cause most of the work in final fairing.
        Easier to grind 'em flat between layups than after the final layup.
    4) I found it easier to do my primary fairing over the next to the last layer of 'glass.
        That way the final skin of fiberglass is being applied over an almost finished surface.
        All the big lows have been filled and the last layer of glass holds everything together.
    5) Wet sanding will show you every ripple on the hull.
        If you are a true anal retentive, avoid wet sanding, you'll never finish.   ;D

    There was no final fairing on the Slipper.
    Sanded off the fiberglass lumps and gloss coated with epoxy.
    A simple workboat finish that turned out better than expected. I lucked out.
    Where I play is all oyster creeks, no use trying for yacht finish on a beater hull.
  6. firecat1981

    firecat1981 BBA Counselor

    True words there my friends.

    I like to mix my own fairing mixes and this last time it worked out very well. I did my fairing the traditional way right before topcoating, but with sanding in between layups and doing a knockdown of all the highpoints and overlaps. It was pretty minimal except over where I had the biaxial cloth because it is much rougher when glassed then woven cloth.

    I mix mine with 4-5 parts, which some might find excessive, but I like how it works out.
    1 - Obviously the resin, either 2:1 or 4:1 if I have it for extended pot life

    2 - micro balloons for added sandability and darker color which helps with leveling and making sure you don't dig into you glass.

    3 - microspheres, I use these to cut down on the price cause they are less expensive then the micro balloons but do almost as good a job. however they are white so they don't give you a contrasting color. I usually did about a 50/50 with the balloons.

    4 - Microfibers! It didn't affect the sandability much, however it will add stregnth to the mix and help prevent cracking from what I am told. I am a big fan of microfibers and mixed just a little into ever fillet and used them heavily in places I bonded and filled.

    5 - silica, sometimes just a little to prevent any sagging when doing vertical surfaces.

    This is just my mix, everyone has a different opinion. I for one will not use products like quickfair because you have a time frame in which it needs to be sanded. With making your own mix I can sand it a day, a week, or a year from now and it will be the same stable mix.