Marine Plywood...

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ferrariman

Petty Officer 3rd Class
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Jan 4, 2006
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I am putting a new floor and transom in my 14ft fiberglass runabout, is marine plywoood nessacery or can i ust buy regular plywood and seal it somhow? Also any tips on putting in a new transom and floor?<br /><br /> Thanx , Ferrariman
 
dave524

dave524

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Aug 27, 2005
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116
Re: Marine Plywood...

No, Marine plywood is not nessessary. regular plywood will work, however, coat it with epoxy and let it dry. This will make it water tight. once your floor is done, roll it with another coat of epoxy to fill any seams you create.
 
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surlyjoe

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Nov 21, 2005
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Re: Marine Plywood...

marine plywood is not sealed, and I have heard its the same glue they use for regular exterior ply. it just doesnt have any voids in it, so teh wood its made of is better quality.
 
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Solittle

Fleet Admiral
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Apr 28, 2002
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Re: Marine Plywood...

You asked about tips - - - They have already been written - - spend a few hours right here reading past posts. Also learn how to use the red Search at the top of the page.
 
jserb

jserb

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Re: Marine Plywood...

hey budd!!! i just finished doing the floor in my 20ft wellcraft. i used treated lumber. i also happen to work at home depot in the lumber department. i sugest you use treated lumber, cheaper than marine ply and a bit more than normal ply, BUT it is the sure fix for your problem. you gotta remember treatred ply can last 20 + years out in the elements!! and i mean thats our side in snow, rain, heat, EVERYTHING 24 7 my deck at my house is 30 years old and still holden up just fine. point is your boat wont see anything like a normal deck or dock would, and treted is made to get wet. im tellin ya you do the normal ply and you will be sorry after a seasion depending on how well you cover it and how much you will use it. Do it right i say!
 
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ljshein

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May 17, 2005
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Re: Marine Plywood...

jserb,<br /><br />I'm in the middle of my 18' bowrider restoration, about to start putting it back together again. My plan is to use exterior grade wood and coat it several times with epoxy.<br /><br />Everthing I've read says don't use pressure treated, the epoxy resin won't bond to it correctly. How did you get past that on yours?<br /><br />Jeff
 
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andy6374

Lieutenant Commander
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Aug 4, 2005
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1,617
Re: Marine Plywood...

I aquired this from another forum:<br /><br />There are at least five areas that differentiate "marine graded" plywoods, from construction grades of plywoods.<br />1- The epoxy used in Marine graded plywood, is typically more moisture resistant that that used in MOST construction graded "built-up" lumbers.<br />2- The woods are selected/sorted to ensure more evenness of grain than construction grade lumbers are required to have.<br />3- ALL individual layers or plys which have holes (typically from knots), MUST be filled with appropriate sized plugs, so that NO voids in excess of XYZ% exist, thus providing a more structurally uniform material, that is not only more predictable, but stronger in shear, bending, and compression.<br />4- The selected woods are also screened based upon natural "oils" (also know as "pitch") content of the wood<br />5- Finally, selected woods are pre-dried, to remove as much "contaminants" (moistures & oils, etc) that could cause adhesion problems, before being placed into the wood presses, for curing.
 
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santa666

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Apr 30, 2003
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98
Re: Marine Plywood...

Please also note that marine grade plywood has more plys per thickness giving more rigidity for any given thickness. <br /><br />The big advantages of marine ply:<br /><br />#1 Quality woods with NO voids for moisture to collect in.<br /><br />#2 Arguably better glues.<br /><br />#3 More plys means stronger wood.<br /><br />The downside is cost. Mine was $71.00/ 4'X 8' doug fir 3/4" (it is beautiful and a joy to work with)<br /><br />I've gone with 3/4 inch for my 17 footers transom, floors, stringers, and bulkheads, all 100% encapsulated... Overkill? maybe, but the best leveler whichever wood you go with is your own skill. Your woodworking skills and your skill with fiberglass should go hand-in-hand. Encapsulation, especially on the end grain is a big factor. <br /><br />I believe a crappy job with the best lloyds of London rated plywood would not outlast a master crafstmans job with average grade wood that recieved full encapsulation and immaculate attention to detail in construction...<br /><br />So, buy the wood you want, but give it the absolute best effort you can.
 
tashasdaddy

tashasdaddy

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Re: Marine Plywood...

are you working on that boat you posted pictures of over on the johnson/evinrude forum.
 
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tr918

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Aug 15, 2004
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Re: Marine Plywood...

If you use exterior pressure treated plywood make sure that the wood is completely dried out. If the wood is still wet from the pressure treatment then it will shrink some and change shape a little. It could pose a problem with floors or structural pieces. There is nothing wrong with using it. Just make sure it is completely dry. If not it could cause you some headaches. <br /><br />-TR
 
jserb

jserb

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Nov 29, 2005
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Re: Marine Plywood...

ljshein , right now, where i live in michigan pressure treadted ply is selling slow, so this means that this ply is left over from the summer and it has now fully dried out, this being said you can then apply the resin no problem!!!! if you go to your home depot and pick through the stack youll find this time of the year its not a big seller and they will have pt wood from the prevous summer. NOW as for sealing it after. i just painted resin (no cloth) over the top of my floor, i just used the resin as a sealer not for strenth. The reason i did not and DO NOT say to seal the top and UNDERSIDE of the floor is becuase if the resin happens to crack, water will get in that seem and will have now way of getting out becuase you have sealed the top and bottem parts of your floor. this inreturn will cause the wood to rot out fast than you could EVER imagin. so i left the bottem of my floor unsealed so that if water did some how get through my resin it would be no problem due to the fact that the bottem side of the floor can "breath" and allow that water/moisture in the floor to evaportate and escape instead of rottin out the floor. like i said marine ply can last decades in the elements and i know a little water here and there wouldnt hert her
 
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PuckHog

Seaman
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Jun 26, 2005
Messages
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Re: Marine Plywood...

The downsides of pressure treated anything is it's poisonous, the newest compound ACQ is extremely corrosive (will corrode anything not HDG or stainless), typically the plywood will be cdx grade at best, the chemicals don't penetrate to the core of the plywood so you have to seal all edges and cuts anyway. Being in the trades using plywood all of the time, I would suggest using Finn ply. It has the most ply's (all made from birch) and no voids to be comparable to marine grade ply, just not the name and additional cost of anything 'marine'. Be sure to paint all sides and edges of your ply with two-part penetrating epoxy sealer and it will last as long as anything. Best of all, the stuff is so much stronger than regular fir ply you'll think you put in steel decking.
 
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ferrariman

Petty Officer 3rd Class
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Jan 4, 2006
Messages
82
Re: Marine Plywood...

Tashasdaddy, this is the same boat i talked about in tha johny/rude forum but i havent posted pics yet. i mentioned i salvaged the boat if that rings any bells, i will post some pics of it asap in this topic even thought it is "underconstruction"
 
C

crab bait

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3,831
Re: Marine Plywood...

yeah,, but birch rots like a garden tomato..<br /><br />doug-fir has very good rot prevent inherent..
 
tashasdaddy

tashasdaddy

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Re: Marine Plywood...

Fman, i'i glad you to our advice to check out the hull before you tear up the water. you are going to have a great project. here agian like your motor take you time and educate your self first. it will save you $. i recommend exterior plywood with all edges sealed before you install it. using card board like appliance boxes make good templates for cutting your plywood.
 
jlinder

jlinder

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Re: Marine Plywood...

I see everyone talks about using epoxy to seal the plywood, and there is discussion about strength of the wood.<br /><br />Is there any advantage to fiberglassing the wood to seal and provide some extra strength? I just don't know how that would affect cost, strength, sealing, and total work to get it done.
 
tashasdaddy

tashasdaddy

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Re: Marine Plywood...

after 35 years working with wood. the pressure treated wood of today is nothing like the old stuff. it is not treated to keep water out. water is the #1 enemy of wood. i dont care if you seal it with epoxy or just a good oils based sand and sealer. just seal it to keep the water out. there are a lot of old wooden boats out there, the reason they have been kept sealed,and protected against water intrusion..
 
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