Using cheaper construction plywood instead of Marine plywood

Discussion in 'Materials' started by DGreenwood, Apr 4, 2013.

  1. Petros
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    Petros Senior Member

    the only differnace between marine grade and contruction grade is the number/thickness of veniers and the number of flaws allowed in each venier. the adhesive is similar.

    If you live in high wind area or in earthquake prone areas (I live in both), you already depend on the quality of the construction grade plywood to keep you safe and keep the building from falling on you. If it is stamped but does not meet the minimum grade requirements it is still defective and a hazard. Most people will spend way more time in their home than no their boat, that means you depend more on the quality of the construction grade plywood to keep you safe than you do on marine grade plywood.

    Whenever I buy any wood, for a home construction project or for building boats I always carefully inspect EVERY piece before I buy it, no matter when I buy it.
     
  2. parkland
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    parkland Senior Member

    If I returned every piece of crap wood I get from the lumber yard, I'd go broke putting fuel in the truck.

    Usually I just find a way to make it work.
    EG 2x4 lumber is always bent like hockey sticks, just stagger the bends in hopes it ends up working.

    Someone once told me, all the good wood from canada goes to china, we get all the crap left over.
     
  3. troy2000
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    troy2000 Senior Member

    I doubt you could replicate the factory conditions well enough to ensure a better product. You don't have the equipment, controlled environment, or quality control.

    There are reasons why commercial contractors buy gluelam beams, instead of trying to build their own onsite.....
     
  4. parkland
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    parkland Senior Member

    That is true, but in fairness I'm sure some wood working experienced guys could probably still deliver a result far better than the OP's picture :)
     
  5. troy2000
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    troy2000 Senior Member

    So could the average factory.

    Obviously, what was pictured isn't a typical example of what's available on the market. I spent most of my life in residential construction, at one level or another. And although I had my share of problems with materials, I never had a sheet of plywood do that.
     
  6. parkland
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    parkland Senior Member

    True enough.
     
  7. rberrey
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    rberrey Senior Member

    One option for ply replacement where weight or bending is not a factor , such as bulkheads is Baltic birch form ply, Russian or Finform. You will have to sand the paper finish off. The fir form plys would be my next pick, if it is bb then you will have to make sure there has been no stripping compound applied . From plys will have few to no voids depending on what you buy , bb mdo or hdo and material used , fir or Baltic birch. The glue will be the same type as marine ply. The layers will be about the same as well. Rick
     
  8. rberrey
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    rberrey Senior Member

    I checked to see what the price and weight were ona boat building site for 18mm meranti BS6566, $105.75 + shipping, 72lbs. 18mm MDO is figured at 82 lbs for shipping out a job , so about 10% more than meranti and 25% more than okoume weight wise. But I did go to one of many places in town that sells form ply three months or so back and picked up three sheets 3/4" MDO at $45 each, with 13 plys and same type glue as marine ply. I wouldn't use exterior ply on a boat when you can buy form ply for a little bit more. Rick
     
  9. DGreenwood
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    DGreenwood Senior Member

    Before making pronouncements about the comparison of the two types, one should read the guidelines for certification or voluntary qualification as marine ply:

    -Yes the adhesive is similar
    -Number of plys does matter.
    -Number of flaws does matter
    -Uniformity of species matters
    -Sanding quality matters
    -Moisture content matters
    -boiling and breaking tests matter

    I could go on.
    It is certainly anyone's prerogative to use whatever you want for construction but any builder that would cut corners at the purchase of essential materials like this does not think about the relationship between the labor intensive job of boat building and the relatively small increase in the getting the best materials available.
    After 35 years of boat building I can say with absolute certainty that cutting corners on materials is naive and will eventually lead to failures that are expensive and unnecessary.
     
  10. SamSam
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    SamSam Senior Member

    If you go there and pick it out yourself and end up with crap, it's your own fault.
    If all they have is crap to begin with, you need to go to a different lumberyard.
    If you order it and have it delivered, order 30-50% too much, use the best and have them come get the rest as a return. Tell them you can't use crap in your projects.
     
  11. DGreenwood
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    DGreenwood Senior Member

    Nor have I. That is a relatively recent phenomena but shows what the factories feel they can get away with these days. Rather than the question "what is the best product I can produce and still make money?" their general business model is "what is the cheapest crap I can convince the public to buy?"
    Counter to this I just took delivery of 100-10' x 2" x 4" from a construction lumber yard and they look like old growth fir. Beautiful stuff about 25 to 30 rings to the inch and knot free. If it were dry I would use in boat building without hesitation. It is a shame to build a stud wall with it! How does this happen?
     
  12. missinginaction
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    missinginaction Senior Member

    I've had absolutely no issues with ply on my restoration.

    Used Okoume BS1088 for cabin roof, weight bearing bulkheads/partitions. Marine grade Douglas Fir for decks.

    I used Araucoply for all my interior ply, the inside cabin sole and my flybridge plywood needs. Coated everything three times with epoxy, a light layer of glass cloth (if exposed), 2 coats primer and at least 2 finish coats of 2 part linear polyurethane paint.

    I can't find any problems at all with the less expensive Araucoply. I will say that I never found a void in the Okoume. I found a very occasional small void in the Auracoply, but not enough to bother me.

    It's available in the US at some but not all Lowes.

    http://www.araucoply.com/informacion2.asp?Submenu=1514&cat=0&fin=0&idioma=44
     
  13. DGreenwood
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    DGreenwood Senior Member

    Excellent choices and application.
     
  14. SamSam
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    SamSam Senior Member

    As to the OP, 5 ply 3/4" plywood is usually not a good thing. 7 plys of even thickness can be pretty solid and stable.

    It depends on the wood species.

    Since compliance to grading rules are "voluntary", as in there are no govt inspectors, the actual company that makes the plywood has a large part in the quality of any particular grade.

    The same product from the same company might vary depending on the quality of the logs that were in the works for that day or week.

    Smaller lumberyards often have better product than the big box stores.
     

  15. Petros
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    Petros Senior Member


    this is not the whole picture, construction grade plywood is certified the same way marine grade plywood is done. there are industry grading organizations such as the Western Wood Products Association (WWPA), the American Forest & Paper Association, the American Wood Council and so fourth, that set the standards for lumber grading. They also train and certify the lumber graders. when the trade organization's grade stamp is put on the lumber, be it sawn lumber, laminated beams or sheet goods, the organization has a vested interest in keeping their licensees in compliance with their guidelines. If a mill is consistently outside the guild-lines they will loose their certification and can not display the organization trade stamp. There is also a continuous random testing of mill output by the organization's labs to verify compliance with their guild-lines.

    So while it is true that the mill voluntarily meets the grading organizations guild-lines, if they are to display the stamp on the lumber they are obligated to meet their guild-lines. building safety is at issue, and all government agencies recognize these industry trade organizations as a legitimate quality control. A mill that is intentionally mis-grading or improperly grading wood will get fined by the state for false labeling and reckless endangerment.

    This process is also true with almost all safety related materials, including the grading of marine plywood and aircraft grade materials, including alloys, composites, fasteners and adhesives. There is no government agency certifying marine plywood either. Nor that tests the fasteners that hold aircraft together for that matter, but rather an industry consensus to a quality standard to maintain safety.

    To say that it is up to the mill to meet the standard is true for marine grade plywood as well as those that make aircraft alloy. Each material is supposed to comply with an industry standard if it is to be labled as such. How do you know that the so-called marine grade plywood is actually marine grade when it comes from the orient? Or from Russia? You do not.

    So, inspect the wood you buy no matter how it is graded. You can depend on a trusted supplier to do that, but no process is perfect.

    If you do not want to use manufactured goods because you do not trust it, you can buy grown lumber, or raw logs, and mill it yourself. I do not think making your own plywood is that difficult if done carefully, this is exactly what is done when you make a cold molded hull, is it not? You are making your own plywood in the shape of the hull that you want.
     
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