Luan reliability?

Discussion in 'Boat Design' started by jalexfolds, Nov 13, 2005.

  1. jalexfolds
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    jalexfolds Junior Member

    I have been building 15 foot solo canoes out of basic Home Depot Luan and polyester resin for a while now and they have held up great but they don't get much hard use. I am planning on building a sea kayak close to 18 feet that will go through more punishment than my canoes. I will be using Epoxy this time, the whole boat will be glassed inside and out with 6 oz. cloth and reinforced at the interior seams with 9oz, 3 inch tape. Will also probably add more cloth to the bottom exterior. Would it be a bad idea to keep using luan? Will voids still be a strength issue with this much glassing? It is really hard for me to find marine grade 1/4 inch around here and the shipping seems really expensive. Thanks for any advice. --John
     
  2. D'ARTOIS
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    D'ARTOIS Senior Member

    Look, I grew up in the environment where we used only Marine Grade plywood - if possible Bruynzeel; Luaun is actually plywood that is used in housing and not in boats. The glue in that is not up to our standards.
    In your hemisphere, it might be different. Again, why don't you use strip planking an after that glassing? Many do and the results are exellent.
    We pay up to 100 till 200 US$ per sheet for good material. If you find gaps in plywood than you use inferior material. There are other solutions than using this material. I can hardly believe that this is the only available material for you.
     
  3. cyclops
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    cyclops Senior Member

    Ocean kayak? That is a different boat, completely. Any one useing it will assume it can carry a ton of equipment. Period. Do not use non marine wood or construction in the ocean kayak. It could be called murder if you use NON MARINE woods. The boat is supposed to be packed full of gear and people if a 2 seater. Marine Ply for the ocean. There is no discussion on this type of boat. Please use only the Marine Ply.
     
  4. tom28571
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    tom28571 Senior Member

    There is lauan and then there is lauan. The basic lauan wood is perfectly good for marine use when protected as you would occume, for instance. There is even some lauan made with marine rating although I have not seen any available lately.

    The closest thing to marine would be lauan rated as underlayment for floors. This is made with "waterproof" glue although I would think that it is not as good as that used in the marine version. Then there is lauan made with non waterproof or even non water resistant glue that is used for paneling and other above grade use in houses and lower grade furniture. Many use this material in boats with the mistaken belief that if it is covered with resin it will be OK but I would not touch it.

    One that I have used is exterior lauan door skins. They are 1/8" and pretty durable. Much cheaper than marine but are generally only available in 3' by 7' size.

    In the end, you are generally better off to use only marine grade if it can be aforded. If it is to be either non marine plywood or no boat, go with the boat.
     
  5. gonzo
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    gonzo Senior Member

    You can get exterior grade fir plywood at Home Depot. It is a bit better than the lauan but not as flat.
     
  6. FAST FRED
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    FAST FRED Senior Member

    The glue in that is not up to our standards.

    Today almost all the glue is fine , as there is now little savings to using interior glue.

    The test is very EZ , take a hunk of plywood and slowly boil it .

    If it holds together for 3 hours its usually fine , if you can boil it for 24 and it is still together its EXCELLENT .

    FAST FRED
     
  7. cyclops
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    cyclops Senior Member

    The boilng is no accurate test . For anything. Unless you boat in Hell. No boat has bare wood in water. ---------------------------American EXT. plywood from HD or Lowe's will work fine if you pick from a stack that has the same type of wood on both sides and has no patches where you will cut. Leave the wood leaning against a garage wall for 2 weeks. As the curve forms it should help in bending any big skins with no risk of breakage. Some sheets refuse to bend, save these for straight areas. Return any twisters as soon as they start. We can build, if we use some logic and patience.
     
  8. Baldur
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    Baldur Junior Member

    :) If you are going to use Home Depot as a lumber supply, they have an MDO ply that uses exterior grade (waterproof) glues and has a nice smooth outer layer. If your Home Depot is smaller you may have to order it.

    "MDO, or medium density overlay, it's engineered plywood with a resin treated fiber applied to both faces. This gives an extremely smooth finish that is easy to paint. In addition it's rated for exterior use, which means it is safe from the elements, insects, or other outdoor hazards, making it a perfect choice for the new deck or porch."

    It works very well for boats too, but should be completely coated with epoxy or epoxy type paint before use.

    Hope this helps.........:)
     
  9. gonzo
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    gonzo Senior Member

    Chris Craft Sea Skiffs were built with MDO and painted with alkyd enamel. 60 years later, many are still going
     
  10. FAST FRED
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    FAST FRED Senior Member

    "No boat has bare wood in water."

    The usual death of every Tiawan Tub is balloney "Composite " construction. This is where the builder does not have the skills to produce a deck & house mould , so simply builds from cheapo plywood and with a GRP paint job it becomes "Composite".

    These boats fail at the 8 to 10 year point if every bit of bedding is not renewed, since this rebedding inclused the removal & rebedding of teak decks , it is seldome done.

    May be hidden but it definatly has "bare wood in water".

    FAST FRED
     
  11. jalexfolds
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    jalexfolds Junior Member

    Thanks for the advice

    Lots of good advice, thanks. Is the glue really what I should be worried about? I have heard most glue is the same these days and its the lack of voids that makes marine plywood marine plywood. While this may be opitimistic(which no boat builder should be I reckon), I feel like no water will ever contact the wood underneath multiple coats of cloth, epoxy and paint. I guess my main question will a void in layers here and there weaken the epoxy\wood sandwich core enough to be dangerous. Also, if I see NO voids from the edges, does that mean they more than likely don't exist. Thanks again for all the input. Oh, I think I found 1/4 inch marine grade fir not to far away, none of my books mention it as kayak building material, any thoughts?
     
  12. cyclops
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    cyclops Senior Member

    The gaps seen from the edge are very bad. The voids in the center of the ply can be outrageous in size and number.
     
  13. PAR
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    PAR Yacht Designer/Builder

    The basic troubles you'll run into with the Lowes/Depot grades of lauan are the extremely thin outer layers and poor construction. In a typical 1/4" sheet you'll see 1/32" faces bonded to a 3/16" core. The longitudinal load bearing of these two thin layers isn't worth trusting. Sometimes (pretty rarely) you'll see some sheets with nearly equal layers available, but these will suffer from poor construction. By that I mean, voids, pith, unrepaired knots in the inner layer, over lapping inner layer butt joints, inconsistent glue coverage, etc.

    You can't expect much for less then 10 bucks a sheet. For a little over 20 bucks a sheet I can get 5 ply 1/4" from a Florida lumber distributor. The plys are equal thickness, the quality of construction is far better and it's a much stronger panel. For a few more bucks I can get a BS 1088 sheet.

    As a rule, the planking stock is some of the best wood used in boat construction, for very good reasons.
     
  14. cyclops
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    cyclops Senior Member

    Par, Could you post the 1/4", 5 ply, EXT. ? name or phone #. I would gladly pay the freight to NJ.
     

  15. PAR
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    PAR Yacht Designer/Builder

    Cyclops, my supplier isn't a retail outfit, requiring establishing an account, business license and minimum purchases. Shipping to NJ on minimum orders of plywood would drive the cost way up. Have you a project in mind and approximate sheet count? I could stick it in with one of my orders and work out the shipping afterward. Have you tried "WoodFinder" (I think that's what it's called) on the web yet?
     
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