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Topic ClosedCDX Plywood for boat flooring

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Bo and Susan View Drop Down
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Direct Link To This Post Topic: CDX Plywood for boat flooring
    Posted: 06/08/2011 at 8:31pm
[In response to Topic: jstatham 1987 Party Barge Rebuild]
 
Welcome  to the forum! I remember reading in a thread, that CDX is exactly the same as marine plywood other than CDX may have a few voids in it. Lowes is carrying 23/32 CDX right now for $17 per sheet. Hope this helps. Have fun with your rebuild.


Edited by Wildcat Dude - 06/09/2011 at 9:36am
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Direct Link To This Post Posted: 06/08/2011 at 9:51pm
  Cdx is a basic cheap common plywood. The only thing in common with marine is the fact they are both wood. It is only rated for a little bit of moisture and for a short amount of time. It can start to delaminate in a short amount of time if it get wet repeatedly. As with most cheaper plywoods there are alot of voids in it and with fewer plys it usually doesn't lay very flat on it's own.
 
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Direct Link To This Post Posted: 06/08/2011 at 9:58pm
and CDX will eat your aluminum after its wet
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Direct Link To This Post Posted: 06/08/2011 at 10:16pm
CDX is a grade of plywood not a treatment process. It stands for grade C veneer on one side and grade D on the other. The "x" means exterior glue is used. CDX can be obtained in various forms of pressure treatment or without any treatment. CDX is commonly used for roof decking. Marine grade plywood also is not necessarily treated but it is a superior grade of plywood with fewer knots and better veneer. There are also other grades of plywood such as AB, AC, BB and so on with the letters relating to veneer grades. The treatment process is not necessarily related to the grade veneer. Yes you can get CDX pressure treated wood that will eat your aluminum but you can also get CDX pine plywood with no treatment which will rot but not eat your wood. You can also get marine plywood and have it treated with the wrong chemicals which will eat the aluminum.  You can also get non- pressure treated marine plywood which will rot in the wrong environment. Generally available pressure treated marine plywood will be treated with CCA (copper chromium arsenate) and not a corrosive treatment but it is possible to have marine plywood treated with say, ACQ process. If I haven't confused it too much a better explanation is here In short don't assume just because you have marine plywood it is treated with a non corrosive pressure treatment that will not rot and also dont assume CDX is treated with a chemical to eat your aluminum up.
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Direct Link To This Post Posted: 06/08/2011 at 11:08pm
I always get a headache reading about all the different types and manufacturing processes of plywood. It's a good thing the pontoon folks know what to use, cause it can get really confusing. All I know is you need a wood (treated with whatever) that can withstand being wet and dried, over and over again for many years without failing and won't harm the aluminum on your boat.
 
I also found these interesting comments while looking around:
 
  • Marine plywood played a part in the 1944 D-Day Invasion during World War II. Many soldiers arrived on the beaches of Normandy in "Higgins Boats," the brainchild of Frank Higgins, who convinced his father, Andrew Jackson Higgins, president of the Higgins Boat Company, that marine plywood was the best material available from which to build the Landing Craft Personnel.

    • Marine plywood is not waterproof; only the adhesive that binds the plies together is waterproof. If you plan to use marine plywood in a wet environment, it should be painted and any joints caulked just as you would with any other material.

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    Direct Link To This Post Posted: 06/08/2011 at 11:32pm
    Rick I guess its not confusing to me just as a wiring harness or diagram for an outboard is not for you although it drives me crazy. Basically you have a piece of plywood. It can be any of a number of grades with no treatment including marine and CDX. The glue is what binds the veneers together making it plywood. You can have a waterproof glue or exterior glue but that still won't prevent the wood from rotting. The treatment process is what does that. Basically untreated plywood has two components, wood and glue. Treated plywood has three; wood, glue and a treatment chemical which can be any number of treatments. You can buy plywood treated with a fire retardant chemical or decay resistant chemical, etc. This wood can be of any grade that is sent to the wood treater including CDX, marine, AC, BC, etc. As for aviation this would be a good example of marine plywood, untreated, being used for its tight/smooth finish and still needing painting/caulking to resist water. Had the marine wood been treated with CCA, ACQ or other processes it would not rot or decay if introduced to water thus the painting would not be a requirement. It boils down to two seperate manufacturing processes. The plywood making process and the treatment process. Once the sheets are made they can be sold as is, untreated, or sent to a treatment plant for the many available treatments. As you said stick to the Pontoon Stuff products and you will be safe for pontoon applications.
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    Direct Link To This Post Posted: 06/09/2011 at 12:29am
    Good info Brian. Maybe you can help with these thoughts. How long do you think the Pontoon industry has been using treated plywood? It seems like we see alot of rebuilds here that are around 15-20 years old (Some more, some less) and the decks are rotted, while others (Such as Charles' boat) are in great shape. If the wood was properly treated, then what is it that's breaking down and causing the deterioration of the wood in the ones that fail more rapidly? I know it depends alot on the environment that the boat is kept in and probably the quality of the original materials used (both wood and glue), but at some point the manufacturers must have decided, hey, we have to start using something that is somewhat standardized so we can compete on a level playing field. Does my cheaper boat use a cheaper wood/process than say a Benninton or Premier might? Seems like everyone offers a lifetime warranty now, so it's hard to tell. Like I say, it's all greek to me..Confused
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    Direct Link To This Post Posted: 06/09/2011 at 8:55am
    I am not sure Rick but I think the old ones used marine plywood with no treatment process. Thats my opinion and not fact. Us Southerners have been using pressure treated for years for termite protection but a properly stored boat that only got the deck wet ocassionally would probably be sound over many years with no treatment. Its the wet/dry cycle that causes the rot. Any wood constantly submerged will not rot. If the wood was pressure treated to the proper levels it should not rot on a pontoon even if stored in wet conditions such as uncovered. To further complicate things too there are various levels of pressure treatment so it is possible for some PT wood to rot if used in the wrong application. I also do know early on there were issues with certain products not being properly treated. The pontoon industry could have gotten some bad batches of plywood and thought they had a properly treated product.
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    Direct Link To This Post Posted: 06/09/2011 at 9:30am
    Originally posted by briankinley2004 briankinley2004 wrote:

    CDX is a grade of plywood not a treatment process.  and also dont assume CDX is treated with a chemical to eat your aluminum up.
     
     
    Every CDX grade plywood I've ever ran across HAS been treated with chemicals that will cause deterioration of aluminum.
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    Direct Link To This Post Posted: 06/09/2011 at 9:49am
    Moved posts from rebuild thread as we have kinda gotten away from the actual rebuild so to speak and it morphed into a discussion on plywood - our aplogies to jstatham for cluttering his thread. We're just trying to make sure that you know what you're doing is the best for you.  The whole point of this discussion though is the marine industry has determined through years of experience what is the best wood for flooring and that has been CCA treated 7 ply layer plywood. Its why PontoonStuff sells it. Lets not talk about aluminum flooring, this is wood we're talking about.
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    Direct Link To This Post Posted: 06/13/2011 at 5:51pm
    Originally posted by Wildcat Dude Wildcat Dude wrote:

    Originally posted by briankinley2004 briankinley2004 wrote:

    CDX is a grade of plywood not a treatment process.  and also dont assume CDX is treated with a chemical to eat your aluminum up.
     
     
    Every CDX grade plywood I've ever ran across HAS been treated with chemicals that will cause deterioration of aluminum.
     
    At least 50% of the houses in my area are decked with CDX plywood and it has zero chemical treatment of a corrosive nature. CDX is your standard C-D veneer with exterior glue and is commonly used for roof decking, sheathing, etc.
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    Direct Link To This Post Posted: 06/14/2011 at 9:40am
    Charles, Bryan doesn't argue computer stuff with you (for good reason!), you would be wise not to argue builder stuff with him.  Big smile
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    Direct Link To This Post Posted: 06/14/2011 at 11:40am
    all I'm saying is, why hasn't the pontoon boat industry used CDX for flooring - because there is good reason NOT to.
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    Direct Link To This Post Posted: 06/14/2011 at 3:29pm
    Which is why I sealed my new deck in epoxy resin.  It will outlive me.
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    Direct Link To This Post Posted: 06/14/2011 at 4:58pm
    I want to play too . I really think everybody is almost right. Charles is correct, there has to be a reason why the industry doesn't use CDX. Brian is correct in his comments also. There are several reasons, and they revolve around the structure of the plywood itself. Plywood plys are graded A (best), B (good), C (bad), and D(worst). CDX could stand for bad & worst, but marine grade appears to be either BB or BC which would be good & good or good & bad. However, the marine bad is better than the CDX bad- if that makes any sense! The quality of ALL the plys in CDX is lower - guess which one has more voids. Also, marine plywood will have 7 plys while CDX will only have 5.

    So why don't they use CDX? (1)Quality of exterior plys, (2)Qualiuity of interior plys, and (3)Number of plys. Better wood, and more layers of it, equals a stronger,more stable product.

    Then there is the treatment issue! Since the marine ply is a superior product, why even go there. The vast majority of CDX, at least in my part of the country, is untreared and used as either decking or sheating in the construction industry. The only treatment I've ever seen is the green stuff, and we know what it does to aluminum. I'm betting that if you could find CCA treated CDX it would work okay, but it wouldn't be much cheaper than PS's marine grade - and it would not be as strong and stable.

    Just my dimes worth!
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    Direct Link To This Post Posted: 06/14/2011 at 5:07pm
    Charles, I was just teasing you about arguing with Bryan who is a builder by trade. I agree, CDX is not marine quality, although pressure treatment chemicals are not the reason.  Terry does a great job of explaining the reasons above, and I totally concur.
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    Direct Link To This Post Posted: 06/14/2011 at 5:31pm
    Oh I know, I was like TeeHee, having some fun. When it comes to construction, I'm coming to Brian for his knowledge (and great house boat wall construction I saw) and maybe he won't throw me off the boat LOL. Its funny thought how we get this big discussion going though about every year or two but its good for the new folks to know. Hug  Thumbs Up   I did find a new thing that was interesting that I hadn't know before was that CDX (all of it) is layered at 90 degree angles whereas marine plywood (like PontoonStuff and Overtons sells) is layered at 45 degree angles for better strength, sanded, polished and voids filled. I think though it'll be worthwhile to find a couple of the guys who have the knowledge in the pontoon boat industry to get their input on why they use CCA wood for their boats. It may have to wait until I get back on my feet in 2-3 weeks but its one of them - you just gotta know why (from the horses mouth)
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    Direct Link To This Post Posted: 06/15/2011 at 1:10pm

    Well I'll be darn, didn't know about the 45* lamination. That would make much stiffer. Thanks for that tidbit of info, WCD.



    Edited by Wildcat Dude - 06/15/2011 at 1:27pm
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    Direct Link To This Post Posted: 06/16/2011 at 12:30am
    OK wood I know but I am not the spokesman for the APA (American Plywood Association). The confusion lies within the treatment process being mixed up with the plywood grading process. Any grade plywood, or wood for that matter, can be treated with any number of available processes. So we must keep the two separate. A #2 2x4 can have the same treatment results as a #1 1x6, a sheet of CDX plywood and a sheet of marine grade plywood. Wood is typically graded then either sold or shipped to a treatment facility. In my opinion I would rather have treated CDX on my boat than untreated Marine grade as I live in LA where lumber rots faster than it corrodes aluminum. Leave an untreated sheet of marine plywood on the ground next to a .40pcf treated CDX plywood sheet for 3 months and see what the termites do. The marine will be toast much sooner. With that being said though the best available product, next to COOSA board, is CCA treated marine plywood. The marine grade is superior for stability and lack of extra surface prep required. The CCA treatment will not hurt aluminum like some other process will. In my area though it is possible to buy CCA treated CDX which will be the same but have large knot holes and lesser plys. It is also possible to buy untreated CDX and Marine grade plywood which neither I would recommend as both would rot if left stored outside for any long period. In any instance PS has you covered as they offer the best grade plywood treated with the best (government restricted) treatment process for contact with aluminum. Its the best of both worlds and at the best prices you will find, less shipping. If all of the above really concerns you go with the Coosa board, you won't regret it.
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    Direct Link To This Post Posted: 06/16/2011 at 11:47am
    Very well put!
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    Direct Link To This Post Posted: 06/16/2011 at 1:47pm
    I like it too Thumbs Up
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    Direct Link To This Post Posted: 07/01/2011 at 10:20am
    I like epoxy.  If I could laminate myself, I would.Wink
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