newbie dumb question

Discussion in 'Materials' started by oldrob, Oct 6, 2019.

  1. oldrob
    Joined: Oct 2019
    Posts: 1
    Likes: 0, Points: 1
    Location: Whanganui New Zealand

    oldrob New Member

    HI all , as a builder of sof canoes beginning in the 1940's and now thinking of building a strip planked canoe I am given to ask if the epoxy glue is stronger than the wood strips and wood is stronger than canvas why would I need to cover the hull with a fabric of some sort having used skin on frame canoes in white water rivers with rocks and submerged trees as hazards and had only two insignificant tears to cope with
     
  2. Blueknarr
    Joined: Aug 2017
    Posts: 659
    Likes: 102, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    Welcome to the forum.

    As was once explained to me:
    All you HAVE to do is breath and pay taxes. Even they are optional if you're willing to accept the consequence.

    The fabric is not used to strengthen the wood as it is there to protect the sealing of the wood.

    Wood is almost an ideal material for boat building. But it has two inherent flaws. It changes dimensions according to moisture content and rots when wet.

    Epoxy can overcome both issues IF a 100% seal is maintained. If the epoxy seal is broken, scratched or chipped, then water can be absorbed into the wood. A small scratch will act as a one way valve, letting water in but not out. The wood swells distorting the vessel and creating additional cracks to let more water in. The wood also starts to rot reducing it structural integrity.

    Fiberglass cloth prevents scratches from completely breaching the epoxy seal.

    You don't have to glass your canoe, if you're willing to accept its quick demise.
     
  3. Blueknarr
    Joined: Aug 2017
    Posts: 659
    Likes: 102, Points: 43
    Location: Colorado

    Blueknarr Senior Member

    An experiment to show how slow semi-sealing dries;

    Three simular rags or paper towels.
    1st as is no baggy.
    2nd sealed in Ziploc baggy.
    3rd in unsealed Ziploc baggy.

    Record their respective dry weights.

    Submerge for five minutes, then hang to dry.

    Record how long it takes for them to return to original weight.

    I predict that the sealed sample will dry in a few minutes. The un-bagged one will take a few hours. The semi-sealed will take a few days.
     

  4. rwatson
    Joined: Aug 2007
    Posts: 5,831
    Likes: 271, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Oh really? 6 oz 110 lbs per inch breaking strength doesn't help 4 mm, random grained soft planks?
    6 oz. Fiberglass Cloth http://www.miapoxy.com/p-174-6-oz-fiberglass-cloth-style-7533.aspx

    My 16ft strip plank WITH 6oz cloth got blown off its stand in 50mph winds, ending some 20 yards down a paddock.
    There would have been some serious cracking of the Western Red Cedar without the glass, but only the hardwood unglassed chine strips broke.
     
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