How many layers of fiberglass cloth?

Discussion in 'Fiberglass and Composite Boat Building' started by MichaelG, Oct 12, 2007.

  1. MichaelG
    Joined: Oct 2007
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    Location: Bourbonnais Illinois

    MichaelG Junior Member

    I'm building my first boat and need to know how many layers fiberglass cloth to use on the bottom. I'm using 6 oz. e-glass, 60" wide? The boat will be about 16' x 4' and plan on going up each side 6" with the fiberglass. I will be covering 1/4" Lauan. Can you use the slow hardners below 80 degrees to extend working time because of the length?
    Thanks
    MichaelG
     
  2. BWD
    Joined: Aug 2006
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    Location: Virginia, US

    BWD Senior Member

    Hard to say.
    What kind of boat?
    Sail, power, oars, all of the above?
    Where will it be used?
    What is the shape (a picture/drawing would help)?
    Etc.
    without knowing all that, I could say if it's a rowboat for a pond, one layer in and out is enough.
    If a power boat for the ocean, lots more....
     
  3. MichaelG
    Joined: Oct 2007
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    Location: Bourbonnais Illinois

    MichaelG Junior Member

    The design will resemble a 16' Jon boat 4' wide 24" deep with a 2inch sub floor. I will use the boat on rivers and small lakes. I'm going to construct compartments for the oars, fishing poles, etc. I will build the boat so it can use up to a 15hp. motor. I have the inner frame started.
    Thanks
    MichaelG
     

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    Last edited: Oct 13, 2007
  4. Moosemiester
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    Location: Ohio, USA

    Moosemiester Junior Member

    Layup Advice

    The number of layers required depends on whether or not the fiberglass is there to protect the wood, and be waterproof, or is part of the structural integrity of the boat.

    Another consideration is the quality of the roving. The 6oz cloth you see on E-Bay ridiculously cheap is little better than simply mixing fibers in the epoxy!!

    I wouldn't worry about using slow hardner, and the working times. I've laid plenty of big pieces of heavy cloth in 80 degree heat using a 4" chip brush and small batches, the trick with epoxy is that once you've got the cloth good and soaked leave it alone, any bumps/strings/piles of fiberglass fuzz mixed with epoxy are easily sanded off once it dries. Using small batches you'll tend to mix the resin better. Not enough mixing makes bubbles!

    Two layers is the absolute minimum, three is better... The more prep time between the layers the stronger the finished product will be.

    HTH
     
  5. MichaelG
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    MichaelG Junior Member

    The cloth glass will do alittle of both, but more to protect the wood and waterproof.
    Thanks
    Moosemiester
    MichaelG
     
  6. BWD
    Joined: Aug 2006
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    BWD Senior Member

    If you have not used epoxy before, I will say, go for the slow!
    Once you have experience, it is easy to do it fast, but if you are like most, the first go will not be that smooth.

    Also, nothing wrong with 6oz, but if you use a 15hp motor you might need strength beyond that of 1/4 inch ply, because you will plane and pound.

    I would guesstimate you would want more like 20+ oz weight of glass on the bottom and transom inside and out.
    also there should be continuous stringers from transom to bow along the bottom, with the frames notched to let them pass through. Using 10-12oz plain weave glass will be easier, less layers....
     
  7. MichaelG
    Joined: Oct 2007
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    MichaelG Junior Member

    Thanks BWD

    I had second thoughts about that 1/4" also. I believe my problem partly is I purchased a inexpensive Jon boat plan and I trying to make it better. I should just build on what I need for my uses. Your input I will use.

    Thanks
    MichaelG
     
  8. Moosemiester
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    Location: Ohio, USA

    Moosemiester Junior Member

    Reinforcing the jon boat

    There's nothing wrong with the idea of using the old boat as a shell for new reinforcement. Three layers of 10oz cloth, using epoxy, properly applied, is amazingly strong.

    I suggest you get the surface good and rough (40 grit minimum), put down a layer, give it a couple of days, sand off the big bumps and little globs of string that inevitably pop up, rough up the whole thing, lay another, and if you've got any big depressions do a little fairing between layers 2 and 3.

    An expert can lay three layers right on top of each other, most of us amateurs can't pull this off! So rely on a good mechanical bond to hold the layers together.

    The nice thing about fiberglass/resin work is that after it dries you can fix your mistakes. The biggest mistake I made in the beginning was trying to get everything perfect while it was still wet!

    I use a 4" disposable brush to lay cloth. Lots of folks swear by rollers. They both work with practice.

    West System is really easy to use, but expensive.

    U.S. Composites is not quite as thin, and takes a little more work to get good saturation, but it's 1/2 the price.

    Being the bottom of the boat I'd use barrier coat additive (West Brand) on all the layers for good measure.

    I haven't used the other brands enough to have an informed opinion.

    And please please wear a really good respirator with a charcoal filter!!

    Let us know how it turns out!
     
  9. PsiPhi
    Joined: May 2007
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    Location: Queensland

    PsiPhi Newbie

    Hi, I've just started my first boat, a 12ft sailing dingy, and had my first enounter with epoxy.
    Living in Queensland as I do, I went down to BoatCraft Pacific and got some of thier BoteCote epoxy resin.

    My first go a brushing the epoxy into the cloth was an unmitigated mess, but I let it dry, sanded off the bumps, and threw the now solid brush away.
    Next lot I used a 3inch plastic spreader/putty knife-ish type thing - epoxy went on much cleaner and much quicker.

    In their book Boatbuilding with BoatCote [AUD$5+pp] BoatCraft say that because the chemical reaction generates heat (which speeds up the cure) if you pour all the mixed goop over the cloth straight away, rather than keep it in the mixing container and apply it a bit at a time, it can disipate more heat and extend (slightly) the working time you have.
    I didn't do this because I wasn't fibreglassing the entire hull, just waterproofing the joins, but found that mixing multiple small batches was not really a problem.

    Oh, and as well as the breathing mask, have a good supply of those disposable laytex gloves.
     
  10. nero
    Joined: Aug 2003
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    Location: Marseille, France / Illinois, US

    nero Senior Member

    Make a test pannel. This will allow you to see if your process is possible.

    The dry method is better. And you may be able to lay all of your cloth dry and wet out the laminates at one time. The test pannel will tell show you how fast your resin will penentrate.

    Keep a heat gun handy. Use it to help kick the resin and to make all the tiny bubbles out-gas. It only takes a little of this ... do not cook the resin. The other advantage of this is for the sides of the hull. It will reduce the viscosity of the resin and keep it from running out of the fabric.

    The process is strange. As you fan the wet glass, many pin point sized bubbles come out. This also makes the resin quite thin, so keep a 4 inch foam brush in the other hand to tip the resin back in to place with. As soon as the heat gun goes away the resin starts to cool and gets to a gel state soon. This is not an exotherm, where the epoxy gets hot and changes color.

    I use washed, ice cream buckets to mix epoxy in. Also a cordless drill with the new style paint mixer work well. The paint mixers are solid twisted black plastic blades on a metal rod. Hardnend epoxy peals off of them. Much easier and faster mixing action than the all metal paint mixers. It pulls silica fillers into the mix quickly.
     
  11. Moosemiester
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    Moosemiester Junior Member

    Interesting Posts

    The posts on this thread clearly demonstrate that there are a lot of different techniques, and that they all work if practiced long enough.

    The heat gun idea is a new one I had never heard of.

    I've found that once you find the right mix of filler and the right brand of epoxy for the job you're doing, bubbles are no longer a problem. But it takes a couple of years to get a good feel for what "exactly" the right mix is.
     
  12. nero
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    Location: Marseille, France / Illinois, US

    nero Senior Member

    Fillers in the epoxy reduce the elasticity. They are great on top of the fabric, but not for between or inside the weave. Sometimes you have to do it anyway.

    The heat gun came from boatdesign.net. It works very well. Becareful. It only takes a few passes to work. I just did one side of my 14.5 meter catamarn hull all by myself. Only way to do that was by the dry method. The heat gun helps keep the work area manageble. Since I am using uni-glass the resin runs out the channels. The ambient temperature has a big effect on the way things work. 90 to 100 degrees the resin is very thin. It requires 2 or more people to do the same job. at 70 to 80 degrees life is wonderful. The resin has a thicker viscosity.
     
  13. Moosemiester
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    Moosemiester Junior Member

    ...

    For most of the stuff I do, a little less elasticity is OK, so adding some cabosil to make the epoxy a little less saggy on vertical surfaces doesn't affect the outcome...

    But I'm working on the decks and superstructure of a good sized boat (36') not a high performance small flexing hull!!
     
  14. nero
    Joined: Aug 2003
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    Location: Marseille, France / Illinois, US

    nero Senior Member

    The elongation of the resin is to match or be slightly more than the fiber that it is used with. Has little to do with the size of the hull. It has to do with the fatigue of the structure. With a big hull like yours it may be very important.

    That said, Sometimes we have to do what we do. smile.
     

  15. sbsboats
    Joined: Oct 2007
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    Location: Ontario, Canada

    sbsboats Junior Member

    you should be ok with fast hardener....just have a friend standing by mixing you up small batches and handing them to you ...MIX carefully!...you want the two ingredients mixed thoroughly....(scrape the sides and bottom of container) and do not whip air into the mix...pour it on and use squeegies to spread it out.
     
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