Marine grade plywood ?

Discussion in 'Wooden Boat Building and Restoration' started by Travis Grauel, Feb 8, 2020.

  1. Rumars
    Joined: Mar 2013
    Posts: 416
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    Location: Germany

    Rumars Senior Member

    Travis, I'll try to respond the best I can, so please don't be mad at me:

    1. Red oak is not usually a boatbuilding wood because it lacks natural rot resistance. It soaks water like a sponge trough the end grain.
    2. Marine ply has 3 important properties. 2 of them are evident, one is not.
    a) waterproof glue. All exterior rated ply has waterproof glue, and usually it's a red-brown colour. You can boil a sample a few times, if the glue holds, it's good.
    b) equal thickness plys. Easy to check, just look at the end of a piece of ply.
    c) no voids. Face plys are easy to check visually, the interior is at the mercy of the manufacturers reputation.
    3. Ply wood species is not regulated. That means marine ply can be made with less rot resistant species.
    4. Plywood absorbs water trough the endgrain.

    What the above means to you:
    You need to protect the endgrain of frames and ply from water intrusion. Any fastener penetration is a pathway for moisture and must be sealed. Thickened epoxy (wich must be painted) is advised for this.

    Your ply choices are probably fir, meranti, okoume, birch, all in exterior or marine quality labels. A good quality ply of a rot resistant species with painted edges needs no fiberglassing. A non-rot resistant species (okoume, birch) will need at least epoxy coating + paint. Fir ply will check so light fiberglassing is advisable. Meranti ply is sold under the hydrotek and aquatek brand names, and quality depends on the individual manufacturer.

    What are your expectations from this boat? You could simply buy some nice fir exterior ply, use thickened epoxy for the edges and paint regularly. It will hold for a while and do it's job. When it rots simply patch it or build another boat.
     
  2. Travis Grauel
    Joined: Jan 2020
    Posts: 29
    Likes: 2, Points: 3
    Location: Maryland

    Travis Grauel Junior Member

    Thanks for the information...I would like this boat to last . I’m planning on doing multiple coats of epoxy fiberglass and paint on the outside with epoxy on the inside. Essentially in my mind that would be waterproofing any wood? Could I use a nice sanded plywood asking as it is thoroughly sealed over and over?? Thanks!
     
  3. Rumars
    Joined: Mar 2013
    Posts: 416
    Likes: 127, Points: 43, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    What do you expect? 5 years? 10 years? 50 years? Epoxy is no cure for bad materials. Test the cheap ply you want to use. Buy a sheet, cut it into 2" or 4" squares and boil some. No voids, no delamination you are good to go.
    How much fiberglass if any at all is debatable. For epoxy look for the cheapest budget brand.
     
  4. Travis Grauel
    Joined: Jan 2020
    Posts: 29
    Likes: 2, Points: 3
    Location: Maryland

    Travis Grauel Junior Member

    Thanks . Any recommendations on cheap decent epoxy? I seem to not be able to find any except 150 a gallon or tabletop epoxy
     
  5. bregalad
    Joined: Dec 2010
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    Location: Georgia

    bregalad Senior Member


  6. Rumars
    Joined: Mar 2013
    Posts: 416
    Likes: 127, Points: 43, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    MAS, System three, East, Totalboat and others. As above, pay attention to delivery costs and be sure to compare prices on the same quantity of finished product (resin+hardener) since mixing ratio and price structure differ.
     
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