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plywood experiment

Discussion in 'Serious Boat Building Questions' started by jdupre', Apr 13, 2013.

  1. jdupre'

    jdupre' Well-Known Member

    Ok fellas, let's not go to the "which plywood is the best" zone. It's not about best or worst, it's about what's serviceable for the job at hand.

    Before I sold it, I put a new bottom on the aluminum sided pirogue. It was sanded pine with an exposure 1 rating. I've been doing a lot of research on the differences between exposure 1 ( as in CDX), exterior plywood and marine plywood. All 3 have WBP glue----water boil proof. By the way, I found out the X in CDX stands for exposure..not exterior.The main difference lies in the way the inner plies are put together. Exposure 1 ply allows more knots, splits and voids than exterior ply so it isn't rated for continuous exposure. Marine ply is much more stringent about defects in the inner and outer plies. Still, marine ply DOES allow SOME deffects......football patches, closed knots and limited voids up to 1/8".

    Now, marine ply is not rot proof. Douglas fir, meranti and okume will rot if it stays wet. Voids in the inner plies can absorb water through unprotected edges.

    Having said all of that, I have yet another experiment going on. I made a 2ft model of a square ended boat out of the scrap sanded plywood. I nailed the small chines in with tiny steel nails and sealed all edges but the gunnel edges with Titebond III glue. The flat faces of the panels are raw wood. I have been soaking and drying the model for several days to test for water intrusion. Soaked half way in a bucket all night and allowed to dry in the sun all day. Went through about 5 cycles so far. I even trained a hair drier (180 degrees) directly on one of the joints at a distance of 1/2" for 5 minutes. Nothing....nada.

    So far.....no decernable change other than the steel nails bleeding into the surrounding wood. One good thing about this pine ply is that the outer plies are about twice the thickness of those of marine okume.

    Not making any rash judgements but, this stuff looks encouraging for a quicky pirogue build. A good epoxy saturation of the edges and a few coats of decent paint and I think this stuff will make a decent boat. If I'm not mistaken, beekeepers boats have been made with similar stuff and have held up well.

    I'm also doing another experiment that will surely start some tongues wagging. :twisted: More on that later .
  2. oldsparkey

    oldsparkey Well-Known Member

    A long time ago some folks called us Wood Butchers for making boats out of wood , I think they missed there calling if they would say the same today.... today it would have to be ...... Wood Tortures. :lol:
  3. Kayak Jack

    Kayak Jack Well-Known Member

    Joey, in CDX, if the X stands for exposure, what do C & D stand for?
    So far, sounds like you're digging deep into plywood. Stuff has been around since ancient Egyptian times.
  4. mike

    mike Well-Known Member

    The "C" and "D" are the grades, or quality of the front and back surfaces, respectively.

  5. jdupre'

    jdupre' Well-Known Member

    What mike said.

    CDX is some pretty rough stuff. It's made to be covered with wall or roof covering. It's rated for exposure so a builder can black in a house and the ply will stand some rain and weather until the house is finished. This sanded ply seems to have pretty good faces..... B rating or maybe even A. NORMALLY, manufacturers don't put real crappy inner plies between A or B faces. Now, CDX can have some scary bad inner plies. A lot depends on the manufacturer..... it's not an exact science.

    Depending on how the production run goes, you could have real exterior ply on an exposure rated stack. No law says they can't give you something better than promised.

    I'm going to continue my test on the model and update the info from time to time.

  6. jdupre'

    jdupre' Well-Known Member

    Jack, Re: digging deep into plywood. Boat building, as well as just about any hobby or craft, has dogmas that somebody started some time in the past, and people from then on spout the "facts" without ever really questioning them. Some of those dogmas prove to be true in the long run and some........not so much. ( see the last line of my signature comments)

    If I can help clarify some tiny portion of the boat building process, I will be satisfied. And to new and not so new boatbuilders, remember that failure is a learning experience too.

    As far as using cheap plywood or other materials............ sometimes you don't need or want a $75.00 meal.... a burger combo from McDonalds will do just fine.

  7. jdupre'

    jdupre' Well-Known Member

    Here is the plywood test model after 10-12 soaking/drying cycles. Most were 1 day soaking-- 1 day drying, but a couple were 2 days soaking -- 2 days drying.


    The white coloring is the glue which gets white on the outer layers when just coming out of the water. The white disappears in a few hours. The black coloration is the steel nails I used bleeding into the surrounding wood. All joints are still tight and the ply looks to be in perfect shape. All edges were coated with glue except the top edges.

    Now, imagine a boat made with this material and glue with 2-3 coats of quality paint applied. Have no proof on how it would compare to "real" marine ply, but my guess it would be favorably.

  8. Kayak Jack

    Kayak Jack Well-Known Member

    Joey, on a real boat, would you consider a coat of epoxy over it all?
  9. jdupre'

    jdupre' Well-Known Member

    Yes I would, Jack. A coat of epoxy would add water protection and would give a harder surface under the paint.

    Just exploring other options in building materials. I still think a glass/epoxy covering is probably about the "best" option, but certainly not the only one. I'll probably build another glass/epoxy boat, but I do like the classic woodworking involved in the traditional build. It's not an "either-or" propositon, but rather just an option that's available.
  10. Kayak Jack

    Kayak Jack Well-Known Member

    BeeKeeper experimented with epoxy both under and over paint. Can't remember which worked better now. My Dad used to mix Water Lox varnish with paint for really tough uses. He never heard of epoxy.
  11. jdupre'

    jdupre' Well-Known Member

    Status of sanded pine ply model: over a month with the whole model exposed to the elements. Approx 15 wet/dry cycles. Same end on all cycles.... shown on right side of picture. Ten cycles, overnite soaking half it's length in water... one day drying. 5 cycles, two days soaking .. two days drying.


    Some discoloration of ply. More discoloration around steel nails. All glue joints still solid. No delamination or swelling. No signs of extreme water intrusion. No checking but the grain is more pronounced on the tested side. Slight warp of one side....maybe 3/16" over the length of the side.

    Not a truly scientific test, but much more rigorous than the ply would encounter in a well finished, painted boat. Ply might check down the road.........but so will fir marine ply .. at 2 1/2 times the price. Do I recommend it? Nope. Just one test of one piece of ply. Just another option to consider. From what I've experienced, I'm satisfied with my choice.
  12. Kayak Jack

    Kayak Jack Well-Known Member

    Nice find, Joey.
  13. tx river rat

    tx river rat Well-Known Member

    This may stir a hornet nest up and it isnt ment to.
    Years ago we use to build ply boats using the chine log method no glass just paint ,they normally lasted a couple years. This is sitting out in the sun rain . The problem with these boats is scratches and gouges that cut into the plys letting water seep in.
    Built boats from epoxy and poly they both work but come up short on lasting and duribility.
    The best I have found is complete saturation coat and a good coat of 6 ounce cloth inside and out .
    If the boats are kept inside out of the weather the effects are slowed way down.
  14. jdupre'

    jdupre' Well-Known Member

    Ron, I would expect a painted wood boat to go bad quickly if left in the elements. I know they can be built to withstand the elements better, but it takes some care and maintenace. I know everyone is not fortunate enough to be able to keep a boat under some kind of protection, but I couldn't bare leaving something out in the rain and sun that I put so much effort into. Big boats I can see, but a person should be able to find a place to tuck a paddle craft out of the weather.

    I would have to agree that complete saturation and glass would make a much more durable boat. That's the direction I seem to be heading for a future build.
  15. Kayak Jack

    Kayak Jack Well-Known Member

    I remember old, wooden row boats - a north woods pirogue, sorta - that were painted. Various resorts rented them out. I don't know for sure how long they'd last, but figure a few tears.
    Glass and epoxy will surely extend the life of a wooden boat, IF kept out of the sun so the life of the epoxy itself is extended. Haven't tested this, but even a lean to with a plastic tarp roof would shade a boat some, and extend its life quite a bit, I'd expect.
  16. jdupre'

    jdupre' Well-Known Member

    The model has been exposed to 6 months of South La. weather. 95 degree days, rain for a week at a time , wet grass clippings and the last month laying on one side in a pile of wet leaves. I just hosed it off and let it dry a bit.



    No delamination other than the 6" long split ( the only one) . No rot whatsoever. The dark stains are mostly the Titebond glue. Remember..... no finish of any kind on the flat panels and none on the "gunnel" edges. Some warping of the long sides. I didn't test the glue joints, but they still seem to be tight.

    I'd say, for someone on a budget or just experimenting with designs, this $24.00 a sheet sanded pine ply is hard to beat.
  17. Kayak Jack

    Kayak Jack Well-Known Member

    You do good work, Joey. You remain objective and show judgement.
  18. jdupre'

    jdupre' Well-Known Member

    Thanks,Jack. Just exploring the options so new ( and veteran) builders can make a more informed decision. Having worked with douglas fir marine ply and this sanded pine ply, I found they cut, sanded and finished about the same.
    Actually, the douglas fir marine ply had a LOT more defects on the surface layers that were fixed with "football" patches. The sanded pine surface plies were almost defect free ........no football patches at all. I did find one 3/16" wide void in an inner ply that ran the width of one of the sides that had to be filled. Not a big deal.

    The hard and soft wood on the pine makes it harder than douglas fir to get a truly smooth surface. That's mostly cosmetic though.

    Two sheets of pine ply, a few sticks of pine for trim, a little glue and nails and you can have a very robust and serviceable pirogue for well under $100. Cheap enough to experiment.

    Nothing wrong with spending 3 or 4 times as much for the "best" materials. But suppose that boat is not quite what works for you. A guy might not be inclined to start another build if the cost is too high, so he might just have to live with the less than perfect boat. I can just about guarantee that the first boat will have some design and building flaws that might tend to grate on a person's nerves. Cheaper materials might be the best route to go until design considerations and skills come up to par.

  19. Wannabe

    Wannabe Well-Known Member

    Thanks for the report. A lot of times young folks with families are very cost conscience when doing fun projects. Thanks
  20. Kayak Jack

    Kayak Jack Well-Known Member

    So are some olde fartes. :wink:

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