Sealing Marine Ply Decking

Discussion in 'Materials' started by CrankyCrankPot, Oct 18, 2005.

  1. CrankyCrankPot
    Joined: Oct 2005
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Detroit, MI

    CrankyCrankPot New Member

    Hello forum,

    I'm new to this forum and have searched and read posts related to sealing marine plywood. But I have not been able to find a definative answer to my question. If somone knows of a link to a thread then please advise. I know forum members, at least on other forums, detest someone wanting handholding without searching/reading on there own first.

    I am in the process of replacing the deck on a 20' pontoon boat. I will be using 3/4 marine ply. $95.00 a sheet at my supplier is case anyone is interested. The deck will be covered on the topside with marine carpet and it will be stored outside year round. At the dock during summer months and in the yard during cold weather. I am anal about maintaining my stuff. So, the boat will be covered at all times when not in use. Snap on canvas cover during summer, tarped during winter. I plan on keeping this boat for a long time and would like this to be the only time that I need to replace the deck if possible. But I may need to replace the carpet at some time in the future. When I tried to remove the carpet on the deck currently I pulled up most of the top layer of ply. The deck that's on there now is nine years old, but the last owner did a poor job of keeping it covered at all. So, now that you know the background, here are my questions.

    Should the ply be sealed with epoxy and cloth? I have read several posts that state you cannot completly seal plywood and it will eventually get a breach. Then the applied epoxy and cloth with act to hold in the moisture instead of keeping it out.

    If it should be sealed, with this allow for easier removal of the carpet in the future should it be required?

    Should all sides, edges, fastener holes, and other holes (control cables, etc.) be sealed? Or, should I leave the underside unsealed so it can "breath"?

    What product/s should be used to seal.

    I would be greatfull for any help and ideas. Thanks in advance for your help.

    Joined: Nov 2004
    Posts: 1,068
    Likes: 18, Points: 0, Legacy Rep: 321
    Location: The Netherlands

    D'ARTOIS Senior Member

    Cranky, before you even touch the topic of strat working, think at the following:

    Many of the things you state, are true but they are adapted to using cloth and polyester resin - that combination wil fall apart after 10-15 years of service.

    With epoxy the transmission of moisture is much slower and if the wood or plywood has sufficiently dried out, it is ready for sheating with cloth & epoxy resin and than it should be capable of a much longer service.

    The glues that are used to bond the layers of wood into a laminate are mostly inferior to anything like epoxy. You could consider to make your own plywood floor, using high grade glues (aerodux or epoxy).
    In that particular case you have a basement that will (most probably) outlive you.

    If you require more info, please come back.
  3. cyclops
    Joined: Feb 2005
    Posts: 1,059
    Likes: 5, Points: 0, Legacy Rep: 38
    Location: usa

    cyclops Senior Member

    A few minor details. If all the deck is already pulled up or not really doing much. Take the time to get the boat very level all around before you cut any panels. Then cut and lay down all the panels. Drill all the correct sized holes in the right places for mounting them to the boat. Drill holes for cables, braces, carpet snaps and any thing else that will have to cut or put a hole in the wood . This is called a " dry fitting ". After everything is located. Then remove everything except the sheets of wood still laying where each sheet belongs. Put location #'s on each sheet. The left front sheet could be #1 and so on. You want a system that gets each piece where it belongs. Now pull all of them up and do the sealing coats. You will seal all the holes edges to prevent rot. --------------------Rot finds it's way into ALL wood on edges of the pieces and holes for things like carpet holddowns. -----------------------------You may have to open up some of the holes it the get too much epoxy in them. Not a difficult job, But you know it will be done right. --------------------------------Get a person to help you pickup and move the plywood, or chipped edges will happen.-------------------DO NOT force any screws into the epoxied wood. they will snap off . Drill the hole a little larger till you can cut the threads without fear. -----------------------------------------If the next size drill makes the hole too big, fill it with epoxy , buy the drill size in between and do it right.
  4. lewisboats
    Joined: Oct 2002
    Posts: 2,330
    Likes: 126, Points: 0, Legacy Rep: 1603
    Location: Iowa

    lewisboats Obsessed Member

    To back up and add to Cyclops' answer, for any holes I do in my ply I overdrill the hole, fill it with thickened epoxy and then drill the hole the correct size into the middle of the plastic filler This gives me a totally protected hole where no water can enter the endgrain of the plywood...A plastic hole in the wood. For big holes I only fill in the edges of the hole so that it is smaller than the finished one then drill it out to size.

  5. chandler
    Joined: Mar 2004
    Posts: 378
    Likes: 2, Points: 0, Legacy Rep: 16
    Location: U.s. Maine

    chandler Senior Member

    Get rid of the permanent carpet. Use something you can remove in the off season. The carpet will always trap moisture between the carpet and sub deck.
    Bad situation with even the best marine ply.

  6. cyclops
    Joined: Feb 2005
    Posts: 1,059
    Likes: 5, Points: 0, Legacy Rep: 38
    Location: usa

    cyclops Senior Member

    And carpet does grow mildew on the under side on hot humid days from food and drinks spilled.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.