inexpensive plywood

Discussion in 'Materials' started by meducks, Feb 8, 2011.

  1. indianbayjoe
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    Location: Lake Champlain

    indianbayjoe Senior Member

    It appears that there is just a layer of some sort of resin or varnish. No cloth evident. That can be filled with some thickened edpoxy then covered with cloth or bi axial and it should be fine. Don't put the old piece of wood back in.
     
  2. lewisboats
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    lewisboats Obsessed Member

    A little history on the wood. It has one quick coat of epoxy...it was applied basically days before I took it on vacation last summer and wasn't at all finished. It saw plenty of water over two separate trips last summer and I ended up dumping it once when the running rigging jammed and didn't spill wind fast enough. I will take PAR's advice and put some heavier cloth on it than I had planned but it is currently sitting in the Garage with a pile of stuff on it as it is still too cold to work on it. I took the picture to show how it separated from the glue line and how it checks...the fix is not hard just a bit more sanding and some more epoxy.
     
  3. Boston

    Boston Previous Member

    the only material that expands and contracts like wood is wood, so why would anyone suggest substituting a large chunk of epoxy for wood when uniformity of movement is key to stability and therefor longevity. Sorry to be the detracting party on this one and I'm sure I'll be land blasted for it but if you want anything resembling a homogeneous surface or of uniform flexibility then it seems reasonable to maintain a consistent product of a single material, IE thin layers of glue and laminated of wood. The moment you substitute a chunk of wood for epoxy you loose that uniformity and therefore the consistency of motion. Its like dropping a 10 inch boulder in a 1 inch aggregate mix. I may be the dissenting opinion in this one but I'll take it to my grave. either carve out a chunk of laminate and replace it or glue back in the defective piece if you want anything resembling the original flexibility, otherwise you beg a deformation over time.
     
  4. indianbayjoe
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    indianbayjoe Senior Member

    I think bostons reply holds more true for planking than it would for plywood in our experence. Over the years anytime we have seen a patch like that in a planked boat, sometimes it might pop out or come loose on one side due to improper preparation but not so much on say a plywod lapstrake hull where a small patch was needed. The plywood moves a lot less and were in an area where over the year the weather certainly changes. The thickened epoxy seems to work well for us in those situations. There is nothing wrong with inserting a wooden plug properly epoxied though.
     
  5. Steve W
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    Steve W Senior Member

    While there is no reason not to glue back in a piece of veneer, unless you are going to go to the trouble of scarfing all four edges of the piece you dont end up with a better (or worse) repair. Most people will just fill it with epoxy and it will be fine, especially where you are going to sheath over it with fabric.
    Steve.
     
  6. lewisboats
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    lewisboats Obsessed Member

    Hey folks...look at the picture again...the so called chunk is about 1/4 inch wide and maybe 1-1/2 inches long and a hair over 1/16" deep. Some thickened epoxy to fill and a sheathing of glass and that ain't goin' anywhere.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Encapsulated wood, doesn't expand and contract to environmental changes, regardless of it being solid wood or plywood. There are several reasons to reuse a hunk of wood that has been knocked out, but most of these reasons are aesthetic or material saving in nature.

    Plywood is a wood product, much like cheese whiz in a can. It's made from cheese, but don't get confused about the differences. Plywood is the same deal and not subject to the same issues that solid material is. Yes, it still can suffer the same indignities, but repairs and the way it reacts to these things are different.

    Unlike solid wood Dan, plywood can tolerate a hunk of plastic embedded in it's surface. In fact, taped seam construction techniques employ this technique on the edges of plywood routinely, without issue. This is because of the manufactured aspect of plywood, which gives it it's dimensional stability. Unlike solid wood, though it will move with moisture content changes, this movement is so slight in comparison that it's a non-issue and divot repair with epoxy is perfectly suitable.

    You are correct in that a solid wood piece should be repaired as you describe, unless it's encapsulated (stabilized) or an engineered material (sheet goods or lamination).
     
  8. Zootalaws
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    Zootalaws Junior Member

    It's a late post to this thread, but what does 'check' and 'checking' mean, with regard to ply?

    And all I can get is Meranti - at US$9 for 4mm, US$12 for 1/4", US$17 for 1/2"... one grade, no waiting. Also no 3/8", 9mm, 6mm... instead we have 3mm, 4mm, 5.2mm, 1/4", 12", 3/4"... and that's your lot.

    So, if I want to build anything, I have the choice of Meranti or...

    Where it says 3/8", it gets 1/2". I am not going to laminate an 8x4 sheet of 3/4mm and 1/4" to get 3/8" - not in this lifetime :)
     
  9. lewisboats
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    lewisboats Obsessed Member

    Checking is small and sometimes not so small splits in the surface ply which may or may not go all the way down to the glue line. It is due to the nature of the way plywood veneers are cut. Most plywood is peeled like a roll of toilet paper, which slices through various grains structures and produces the patterns you see on it. If you have ever seen plywood that has been left out in the elements uncovered you have seen the surface with small cracks and tears... sometimes even splinters lifting. This is severe checking. Less severe checking occurs even under paint when exposed to the sun. The surface moves minutely but also unevenly and this results in the micro tearing. Epoxy and Cloth stabilize this and prevent checking.

    The meranti plywood you are talking about is not worth building a boat with. The glue is probably not waterproof, the core is like a sponge and it's surface veneers are onion skin paper thin. A decent marine meranti plywood...aquatek for example...will run you around 40-70 dollars per sheet depending on where you are and where it comes from...not including shipping. It has 5 even plies, very minimal voids on the interior plies and has a waterproof/boilproof glue that will stand up to immersion and long term exposure without delaminating.
     
  10. Zootalaws
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    Zootalaws Junior Member

    The stuff I get is straight from the factory - it is waterproof, has nice even plies, no voids or fills - that I have found, and I use lots of the stuff. I haven't had a problem with delamination yet and it's what all the boats are made of in this massively river-traffic-oriented island.

    The reason it's cheap is because I live where it grows and where it is made into plywood for the Japanese and European markets, not because it is crap. Shipping costs are negligible.
     
  11. lewisboats
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    lewisboats Obsessed Member

    must be nice... [​IMG]
     
  12. Zootalaws
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    Zootalaws Junior Member

    There are downsides - limited sizing, no 'grade A' surface - lots of sanding/filling. But fuggit, the price is right, right? ;)
     
  13. frank smith
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    frank smith Senior Member

    Acx very good stuff for cheap skiff . Why not?

    Get 15 years then cut it up and taker to the dump. Just make sure to keep fresh water out for the most part . I like a layer of glass in epoxy on the c side which I put on the outside .
     

  14. frank smith
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    frank smith Senior Member

    When using doug fir , I like to let it check first , then go over with epoxy ,
    give it a light fill using thickened epoxy applied with a taping knife.
    Put cloth on with a squeegee , and go back to fill the weave .
    If it is a hot day and you move fast most of it can be done.
    Careful application , and little filling is needed to get a decent work boat finish.
     
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