Mix plywood and foam under fiberglass

Discussion in 'Fiberglass and Composite Boat Building' started by MaddMatt, Dec 7, 2020.

  1. MaddMatt
    Joined: Oct 2020
    Posts: 11
    Likes: 0, Points: 1
    Location: buffalo ny

    MaddMatt Junior Member

    Looking for guidance on something I've been struggling to understand.

    In building a fiberglass over ply boat, I understand that fiberglassing the interior as well makes for a stronger finished product. What if I want to add foam to the hull walls to provide some insulation? Do I fg the ply first, add foam and fg again or epoxy foam to ply and then fg? Is there some other method?

    Thanks, inquiring minds want to know!

    Matt
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    When you mention 'fibreglass over ply', are you planning on using polyester or epoxy resin?
    Epoxy would be preferable, never mind that it costs a bit more.

    What size and type of boat do you want to build?
    If I was going to add foam insulation inside the hull, I would definitely fibreglass with epoxy (or at least apply a few coats of epoxy resin) to the plywood first.
    And then consider how I might attach the foam.
    Do you just want the foam to be under the cabin and deck, or on the hull topsides as well, going down to the waterline?
     
    Last edited: Dec 8, 2020
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I would say don't glass over your insulating foam, actually ply is not useless as an insulator, and you might find the foam is not necessary, depending on the area of course. If you find you want insulation, you can just stick it up with a cheap glue later.
     
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  4. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Foam is after glassing. That foam is not considered structural.
     
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  5. MaddMatt
    Joined: Oct 2020
    Posts: 11
    Likes: 0, Points: 1
    Location: buffalo ny

    MaddMatt Junior Member

    Thanks everyone!

    The plans are for straight fiberglass over plywood. I was figuring on epoxy for the resin.

    I was thinking of how to finish the interior and considering a painted fiberglass finish in areas but I'd have to cover up some of the structure to make it a level surface. I can just as easily come up with another option though.

    Thanks!

    Matt
     
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