Marine grade plywood ?

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

  1. Rumars
    Joined: Mar 2013
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    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.
     
    Will Gilmore likes this.
  2. Travis Grauel
    Joined: Jan 2020
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    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
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    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
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    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
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    bregalad Senior Member

  6. Rumars
    Joined: Mar 2013
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    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.
     
  7. West Denny 33
    Joined: Aug 2020
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    Location: West Dennis, MA

    West Denny 33 Junior Member

    "Epoxy is no cure for bad materials. " So are you saying that if you cover the wood with fiberglass, epoxy and paint water will still seep through or moisture will somehow occur within the let's call it the fiberglass encapsulation
     
  8. gonzo
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    gonzo Senior Member

    If that were true, all the cored composite would be falling apart. Balsa cored boats have been around for many decades. They fail through negligence or improper repairs.
     
  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Travis probably has the boat half done by now.

    The issue with some materials is they can be very poor. I bought 5/8 construction ply for a project from the orange store and it delaminated when I screwed into it. Does anyone think if I had complained HD would have rtv'd the entire order? Ha!

    All the exterior materials in the world can't fix those panels. The glue was either deficient or insufficient or some such. A boat is so much work; why consider possibly poor materials?

    The epoxy for my build was very costly. But I have used other epoxies that were absolutely not good for outgassing. Shall remain nameless here.

    Sourcing for one off builders is always harder. But last thing you want to do is build with junk.
     
  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    There are really poor quality materials. I would take into consideration the difference in price and time between what you are building and a skiff though. For a first time builder, learning boatbuilding techniques is more important than durability. Most likely he will use the boat and find out the next one will be improved and better.
     
  11. Travis Grauel
    Joined: Jan 2020
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    Travis Grauel Junior Member

     

    Attached Files:

    cracked_ribs likes this.

  12. jbo_c
    Joined: Jul 2017
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    Location: Gainesville, GA

    jbo_c Junior Member

    Good for you!!

    which wood did you end up using?
     
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