Need help fiberglassing and painting flat bottom skiff

Discussion in 'Fiberglass and Composite Boat Building' started by SamC, Sep 22, 2019.

  1. SamC
    Joined: Sep 2019
    Posts: 20
    Likes: 1, Points: 3
    Location: Fulton county Ga

    SamC Junior Member

    Hi
    I have finished building my plywood skiff and the next step is to fiberglass it. I have researched some on how to fiberglass plywood, but I still have a fiew questions.
    What type of cloth and resin should I use? How do I add more lairs of fiberglass? I want about 1/4" thickness. Where should I buy the materials? How do I paint over fiberglass?
    This will be my first time fiberglassing anything and I would appreciate any advice from experienced boat builders

    Thanks in advance
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Are you going to use the boat where it will be hitting rocks on a regular basis? Otherwise, 1/4 inch is way too much.
     
  3. SamC
    Joined: Sep 2019
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    Likes: 1, Points: 3
    Location: Fulton county Ga

    SamC Junior Member

    No, just for use on lakes and maybe bays
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Can you post photos and a description. For example, thickness of the materials and speed expected.
     
  5. SamC
    Joined: Sep 2019
    Posts: 20
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    Location: Fulton county Ga

    SamC Junior Member

    It's 12' long 3' wide and 2' tall. The bottom of The boat is 5/8" thickness and the walls are .3" . It is a 90 degree angle where the bottom meets the walls. I'm also a new boat builder and I didn't use marine grade plywood because I didn't want to invest a lot in my first boat
    IMG_20190920_184008.jpg
     
  6. SamC
    Joined: Sep 2019
    Posts: 20
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    Location: Fulton county Ga

    SamC Junior Member

    And I'm not sure about the speed, but I do want a motor more powerful than a troling motor
     
  7. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    SamC
    Welcome to the forum.
    Oh, how I wish you posted here much sooner.

    The good news is your boat will float.
    The bad news is it won't have a long life. It might be less effort to start again with marine plywood than to sufficiently seal the existing plywood. Did you use exterior or interior plywood?

    First. to last for very long. the plywood needs to be completely encapsulated with resin. Especially between the plywood and frames. You should take everything apart, seal all the surfaces of all the individual pieces, then put it back together.

    Second. Fiberglass cloth is difficult to apply to sharp corners. Round off all the corners of the plywood while you have things apart. The inside corners ought to have a thickened resin fillit to prevent the cloth from having a gap where it won't lay fully into the corners.

    Thirdly. Don't short cut applying the FG cloth and resin. Pre seal all wood! Then glue on the FG fabric. Some people try to seal and fabric in one step. Some of the resin is soaked out of the cloth into the wood leaving the fabric resin starved and not well atached.

    Fourth. You could greatly reduce the dimensions of the framing. Eliminating most of it if you add a gunnel.

    Or (my personal recommendation) spread a gallon of oil based paint in it as is. Get a year or two of use while you make its replacement.
     
  8. SamC
    Joined: Sep 2019
    Posts: 20
    Likes: 1, Points: 3
    Location: Fulton county Ga

    SamC Junior Member

    If non-marine plywood is completely sealed in resin and protected from sunlight, how long will it last? I will replace the walls with marine plywood, but I'm afraid the bottom cant be replaced without replacing most of the boat. I made the boat mostly for practice and know it won't be my best but would like it to last a while
     
  9. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Interior plywood will delaminate in a few months. Exterior could last a few years. Marine could survive decades.

    The trick is getting the plywood fully sealed where the framing is.
    The joints will flex. This cracks any resin bridging the framing and plywood. Water wicks into the cracks and does its destructive work.

    I would chalk it up as a hard lesson learned. Use lots of paint. Use it for awhile. Learn what features you like or dislike. Then build another you will like better in a couple of years.
     
  10. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    With plywood as thick as you used, there is not need to fiberglass over the whole thing. For waterproofing, you can use a layer of 1.5oz mat and polyester resin. Remember to round the edges.
     
  11. SamC
    Joined: Sep 2019
    Posts: 20
    Likes: 1, Points: 3
    Location: Fulton county Ga

    SamC Junior Member

    So I'm about to waterproof the boat and I looked up "1.5 ounce mat" and I keep finding "chopped strand 1.5 ounce mat" aswell as products that just say "1.5 ounce mat." Is there a specific type I should get?
     
  12. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Mat is made from shop strand.

    What resin ate you intending to use? Epoxy or polyester?
     
  13. SamC
    Joined: Sep 2019
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    Location: Fulton county Ga

    SamC Junior Member

    I'm going off of Gonzo's suggestion of using 1.5 oz mat and polyester resin for waterproofing, do you think that will work? Honestly I really don't know anything about fiberglass and the difference between epoxy and polyester.
     
  14. Blueknarr
    Joined: Aug 2017
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    Likes: 99, Points: 28
    Location: Colorado

    Blueknarr Senior Member

    I hate to use generalities. Because the Law of Fingers syates that for every rule of thumb there are four fingers pointing in other directions.

    Polyester is considered "less than" epoxy. Less expensive. Less water resistant. Less bonding strength. Less pot life (working time). Less pleasant to smell. Polyester might be less than epoxy, but it can still be adequate. I wouldn't leave a polyester coated wood boat in the water for longer than a week at a time. If you plan on storing the boat in the water use epoxy.

    Polyester has a bad reputation when used over wood. I blame most of the failure to poor craftsmanship. Trying to bond fiberglass to unsealed wood is folly regardless of resin used. Seal first, then bond FG to the sealed and sanded wood!!!

    Mat FG on plywood is good. I add a layer of woven FG bridging joints or seams in the plywood. 3" wide knit tabbing tape would do well. Apply an additional cost of resin after the cloth has kicked. Then spread fairing compound (bondo) over the whole thing. Sand smooth and paint.

    Lots more little details.

    Once the outside is done. Try removing most of the inner framing. It will be very difficult to lay cloth over the existing frames.
     

  15. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    I've built a few skiffs with exterior plywood and polyester/mat on the seams. With one coat of paint, and left outside in the weather, they lasted more than three years.
     
    Blueknarr and ondarvr like this.
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