Testing and criteria for suitable plywood

Discussion in 'Materials' started by Wckoek, Jul 24, 2017.

  1. Wckoek
    Joined: May 2016
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    Wckoek Junior Member

    There are good exterior grade ply and there are poor marine graded ply and they are not uniformly graded, and often times marine ply are expensive/not available on certain regions of the world.
    If you have to use exterior graded ply for building, how would you guys determine the quality is up to par?
     
  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    The boil method is most common. Boil a piece of plywood for an hour. If it doesn't delaminate it will be OK>
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Some of the interlamite adhesives will survive a 1 hour boil. Depending on the standard, a sample should survive a 4 - 8 hour boil, plus the cool down and reboil cycle(s) to be acceptable as a WBP type 1.

    When making these determinations, you're best off contacting the supplier and getting a definitive answer or performing the type i test yourself. Most of us rely on known suppliers and though occasionally we've taken a beating, the vast majority of time, they want our return business so come clean on the real physical qualities of their offerings.
     
  4. Wckoek
    Joined: May 2016
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    Wckoek Junior Member

    Unfortunately I won't be able to access to a supplier to ship for the smaller amount I would use in the region (Japan), so I would have to use what they have, and likely the seller would be more familiar with the building side of business than using it on marine, but they do have high quality ply, I'll ask for a sample and test myself.
     
  5. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    Besides the mandatory boil test you need to look for voids in the inner layers. Buy a sheet and cut it up in 10cm squares. If you find lots of voids, look for another supplier. The plys should also be all of the same species and of the same thickness.
     
  6. UNCIVILIZED
    Joined: Jun 2014
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    UNCIVILIZED DIY Junkyard MadScientist

    Generally speaking, more layers per thickness of plywood, & even layer thickness throughout the entire piece is found in higher quality plywoods, where such isn't the case in lesser ones. And by simple reasoning anyway, if one layer is significantly thicker than the others, it'll have different bending characteristics, non?
     
  7. TonyBR
    Joined: Jul 2017
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    Location: Brazil

    TonyBR Junior Member

    Hard to trust anything these days, so I tested myself many samples (10 x 10cm blocks of 6mm, 12mm and 18mm thick WBP plywoods) from different brands with this sequence:

    a) imersion for 12 hours
    2) freezing for 6 hours
    3) boiling for 2 hours
    4) freezing for 12 hours (the idea here was to force delamination from inside out with ice forming within the water that would permeate deep inside after boiling)
    5) microwave (right after freezing) for around 2 minutes watching for vapour/smoking
    6) imersion for 12 hours
    7) boiling for 4 hours
    8) freezing again....6 or more hours
    9) microwave until smoking (wife alert, wife alert!!!)....
    10) cool down and forcing delamination with a sharp tool (chisel)....

    I was amazed that almost all samples survived quite well these tests....
     
  8. srimes
    Joined: Sep 2008
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    srimes Senior Member

    I got burned once using 5-ply luan used to build an 8' pond boat with my boy. Boiled samples and they did great, but once the boat was built and painted there were bubbles all over where there wasn't enough glue. It was the right type of glue, but they had production problems.

    I've had good luck with luan before that boat, and still got some good use of that one. For a quick-and-dirty boat I'd use luan again, but test a little better by spraying the panel to see if it bubbles. If I'm spending hundreds of hours on a boat I'd want more confidence in the materials.

    It's really a risk/reward question.
     
  9. TonyBR
    Joined: Jul 2017
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    Location: Brazil

    TonyBR Junior Member

    Interesting and scaring. Can you please explain a bit more what you mean by "spray the pannel"? We're soaking all wood with epoxy, laminating both sides etc... thanks Tony
     
  10. srimes
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    srimes Senior Member

    Spray some water on it and see if the outer veneer bubbles up.
     
  11. gonzo
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    gonzo Senior Member

    Are you saying you spend hundreds of hours on an 8' pond boat?
     
  12. TonyBR
    Joined: Jul 2017
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    TonyBR Junior Member

    Ohhh....well, after all the testing we made, spraying the surface is a bit easy on the material! :) I tought you sprayed something more agressive than water.
     
  13. Steve W
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    Steve W Senior Member

    As a point of reference BS1088 calls for 72 hours in boiling water as the preferred test for bonding, there are two other tests with steam that are acceptable but in a dispute the 72 hour boil test is used. I don't think epoxy would survive but is obviously good enough ( not used in plywood manufacture)

    Steve
     
  14. PAR
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    PAR Yacht Designer/Builder

    Epoxy (generally) doesn't pass the type 1 WBP test, which is why you shouldn't park your boat over active underwater volcanoes. This said, most of the usual marine grade, room temperature cure formulations can pass, but are dramatically weakened. Additionally, there are epoxy formulations that can and do pass this test, but they're not common with wooden structures, though can be in composites.

    To define this further, room temperature cure formulations don't pass the boil portion of the test, but are waterproof, even along joint line failures after boiling tests. What this means is you need to protect these formulations (fillers, insulation, etc.) in higher heat situations (engine rooms, etc.), so you can get the performance you desire.
     

  15. TonyBR
    Joined: Jul 2017
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    Location: Brazil

    TonyBR Junior Member

    Exactly.... too much emphasis on the wbp plywood tests wneh the Achilles tendom of the entire boat (with higher temperatures) is on the epoxies that are not heat cured. Right now I´m choosing a heat cured epoxy combination to usejust inside the engine "box".... But good insulation will follow anyway.
     
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