Get hull surface even?

Discussion in 'Fiberglass and Composite Boat Building' started by andysailor, Nov 10, 2017.

  1. andysailor
    Joined: May 2017
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    Location: Sweden

    andysailor Junior Member

    I have sanded off the old paint from one side of the hull. In many places I have grinded out gelcoat cracks and other voids, filled, and sanded. But...

    This side is very uneven. Have tried to go over it all again and fill up the uneven, but it's just not that easy.

    Would a high build epoxy help me?
    Or any other ideas? The rest of the boat has turned out much better, but this side haunts me
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    When you say you sanded after filling, exactly what was the method of sanding ? To get a less uneven surface, you need a sanding long-board that won't create local depressions.
     
  3. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    And how big is the boat and how much of the time will it be in the water? It can make a difference in the products used.
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    You need to "fair" the boat, then you'll want to smooth the hull. No, they're not the same. Fairing is what you see, while smooth is what you feel. For example, if you have a golf ball dent in your freshly waxed and polished car door, it's likely still quite smooth, but the eye easily sees the unfairness of the dent.

    What you need to do is identify the low and high spots around your hull and this is simple with a "guide coat". Once long boarded, you'll see all the sins of the grinding. My site has a "Tips & Tricks" section that briefly describes the process.
     
  5. andysailor
    Joined: May 2017
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    andysailor Junior Member

    The boat is 46ft trimaran and will be in thw water all the time.

    The hull/ama was sanded with a orbital sander and polish machone to tet all topside paint off the boat.

    The question now is how I shall proceed. More filler, epoxy high build, sand more on the gelcoat(some areas the fiberglass is shown),
    I have tried some with a one foot longboard, not very long, maybe try to build me a 2ft board.
     
  6. andysailor
    Joined: May 2017
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    Location: Sweden

    andysailor Junior Member

    I ha
    Thanks!
    Good ingo on your website!

    Does it matter what kind of paint to roll or spray the first coat with, the one to get the hull all in one color

    How much would a tool like this help me?
    Products | Flexisander http://www.flexisander.com/en/products
     
  7. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The Flexisander is a tool that some professional might use, but for a one off, hard to justify in cost. Fairing and smoothing operations are simply a necessary evil and if done right, makes a cheap job look great. There's no real short cuts, you either get it fair or there's going to be waves, humps and bumps. The same with making it smooth, it is or is still needs more effort.

    Use a regular primer for the first coat, as you'll sand much of this off on the first pass with the long board. Once you've identified high and low spots, knock down the highs and if the lows are shallow enough, use a high build primer. If the lows are too deep, you'll need filler.
     
  8. andysailor
    Joined: May 2017
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    andysailor Junior Member

    Thanks again!

    Does it need to be a two part component primer to use for detection of high and lows?
     
  9. PAR
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    PAR Yacht Designer/Builder

    Again, any primer will do, you'll sand much of these initial coats off. The coating doesn't need to be heavy or thick, just the opposite is necessary to identify the highs and lows. Most use a cheap rattle can, lacquer style, because it wipes off easily with thinner.
     
  10. andysailor
    Joined: May 2017
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    Location: Sweden

    andysailor Junior Member

    Sorry for all novice questions :)
    So when If I use a cheap regular primer, sand most off it off, detects some low spots. Is it ok to put a two component fairing compound on top of the cheap primer in those low spors? I want to be sure the fairing compound will have a good surface to stick to.

    What size of sanding longboard do you recommend? No extreme curves on the hull or amas. Same question for spatual

    Another question....
    I have used a polyester based filler which contains silica. Maybe similar to Bondo? I have noe rad so many negative opinions about polyester filler. Shall I sand it all off before I start the fairing process?
     
  11. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    The cheap primer needs to be removed before you go over it with a better product.

    Silica isn't a problem, talc and cheap base resins are, so depending on the polyester compound it may be OK....or not. Bondo is bad. Epoxy is better.
     
    Last edited: Nov 14, 2017
  12. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Junior Member

    I recommend a visit to your local auto+body paint supply house to see what selection of sand papers, longboards is available. Your board needs to mate up with available papers. No matter how it is sliced 9x12 paper will not work with a 24" board.

    I fair with a stiff board and smooth with a soft one. The stiffness determines wether the surface conforms to the board, or if the board conforms to the surface. My favorite fairing boards are made from core foam.

    PAR's sight gives much good advice. Pay attention to the many forms of feed back your board provides. How it moves, sounds and flexes will tell how things are progressing.
     

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

    PAR Yacht Designer/Builder

    Paper is best purchased on rolls, not sheets, which gives you the option of any size long board. You can now buy commercial long boards, though most just make them up as needed. I have several of different lengths and widths, from about 6" to 24". I use 1/8" acrylic, 1/4" acrylic, 1/8" and 1/4" plywood for the majority of the board bases, with handles and paper clamps as they can be arranged. I doesn't need to be fancy, just bend uniformly for the area involved. Additionally, it's often wise to slide a skinny piece of soft rubber or foam between the paper and board, so you can "float" it over stuff. It really a process and once you get your head around it, thing will go better for you.

    Yes, remove the primer when you need to fill a low spot. You'll use more to see if it's be fixed anyway. A light dusting is all that's necessary with the primer. Log onto auto-body forums to find the way they do "blocking" (fairing) and "flattening" (smoothing) operations. It's the same thing, just on less round objects, with different terminology.
     
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