Need to decide, epoxy, CPES, and/or Fiberglass?

Discussion in 'Wooden Boat Building and Restoration' started by Guest, Aug 30, 2003.

  1. Guest

    Guest Guest

    I'm new to this forum, but I am looking for "outside" opinions. I'm building a 19' douglas fir plywood sailboat (Weekender design). I am already using Smith Coat Clear Penetrating Epoxy Sealer (CPES) inside and out. This reportedly is made with "natural" wood fibers etc....adding a "flexible" finish. My sources (that are building or have built the same boat) say to fiberglass because the sun will "check" the paint eventually...something about the way the wood is milled or something, the uneven moisture throughout the wood will check the paint if glass cloth isn't used. Others swear by the Smith's Coat and as long as I paint the "half-cured" CPES, it will never check. Both sides of the argument is compelling. Also, I really wanted to epoxy the interior of the boat in order to add a durable finish (in case I drop an anchor or something). But some say the wood wont breathe if moisture gets in...so they recommend not epoxying the interior. If the boat is CPES'd, than is moisture intrusion really an issue here? I just can't get a good consensus of the two above situations. By the way, the doug fir plywood ranges from 1/4 to 1/2 inches thick and it is NOT marine grade. I will be painting the hull with some form of interlux paint, and using epoxy, sand, and paint on the deck (for traction). The boat will probably have very few "bright" areas...due to the plywood construction. Any takers on these questions?
     
  2. rjmac
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    rjmac Junior Member

    I am already using Smith Coat Clear Penetrating Epoxy Sealer (CPES) inside and out.

    I am not familar with this product, sounds interesting, go a website to check out...?

    This reportedly is made with "natural" wood fibers etc....adding a "flexible" finish. My sources (that are building or have built the same boat) say to fiberglass because the sun will "check" the paint eventually...something about the way the wood is milled or something, the uneven moisture throughout the wood will check the paint if glass cloth isn't used. Others swear by the Smith's Coat and as long as I paint the "half-cured" CPES, it will never check. Both sides of the argument is compelling. Also, I really wanted to epoxy the interior of the boat in order to add a durable finish (in case I drop an anchor or something). But some say the wood wont breathe if moisture gets in...so they recommend not epoxying the interior. If the boat is CPES'd, than is moisture intrusion really an issue here?

    The real problem is that the wood degrades by being attacked by bacteria, that is what breaksdown the cellulose structure in wood. All wood has a certain amount of mosture content, it needs it to function.

    All materials absorb a certain amount of water, in fact polyester, epoxy, vynalester(sp?), plastics in general, etc all have a measurement of how much water is absorbed by their product (exprested in a a % or wt). So prolonged exposure to mosture will determine the lifespan of a epoxy wood boat, structural saturation by mosture which is the second failure mode, but is a much slower failure mode.

    Based on this, coat it inside and out with csm..... natural fibers only introduce prosity for bacteria to get to the wood....., which is a very rapid deterioration rate. There is also some structural strength increases by using csm with epoxy besides also checking creep.

    By the way, the doug fir plywood ranges from 1/4 to 1/2 inches thick and it is NOT marine grade. I will be painting the hull with some form of interlux paint, and using epoxy, sand, and paint on the deck (for traction). The boat will probably have very few "bright" areas...due to the plywood construction.

    I have been down this road....... The first and only boat I built by myself was a 14ft daysailer, my first design. I cheapied out and used exterior grade plywood and I paid the price for it. Every year I would have to fill soft spots and refinish the boat.......

    The difference between marine grade and construction/exterior grade plywood is the knots in the marine grade are filled by the manufacture, where with exterior grade it was not. The glue is the same for both but you will have to deal with the voids in the veneer layers, unless your epoxy product can saturate all the way through, even then it is a risk. I ended up junking the boat because I did not feel it was safe to sell, kept the hardware. My dad told me not to do that but he let me make my mistakes. The 28ft'r I am working on will be a different story,,, no cheapying out on this one.
     
  3. Corpus Skipper
    Joined: Oct 2003
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    Corpus Skipper Hopeless Boataholic

    There are several builders around who fully encapsulate plywood with epoxy, decks, cabin soles and tops have been built this way for many years with no problems. Just make sure ANY penetrations through the wood are thoroughly bedded in 3M 5200 or something similar. Also, your location plays a role. Wood will last much longer in cold salt water than warm fresh water. Will your boat be dry stored? If so, I'd think with proper care, it should last indefinitely. If water can't get to the wood, rot should not be a problem. Virtually ALL commercial fishing boats around here are epoxy encapsulated plywood, and these guys' lives depend on their boats. :D
     
  4. duluthboats
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    duluthboats Senior Dreamer

    Lots of stuff here, I’ll start with the Weekender is a large enough boat that I would want to use marine plywood. The hours spent building balanced against the added cost would tell me to use the best I could find. This is not a weekend project.

    CPES is thin epoxy; it will do a great job of sealing your plywood and provide a good surface for paint. It will not stop your plywood from checking. A layer of glass set in resin will hide most if not all of the checking, but not stop it. The checking is going to happen with cheap plywood and some expensive stuff as well. If that doesn’t bother you, seal everything with CPES and then paint it and keep it painted. The biggest reason for rot on a wooden boat is poor maintenance, and no amount of magic coatings can make up for that. If you don’t want to see the checking cover the plywood with glass or other fabric set in resin.

    Have you looked at MDO, it’s plywood with a resin set paper face. The paper is there to hide the checking and provide a smooth surface to paint.

    Gary :D
     
  5. gonzo
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    gonzo Senior Member

    Fir will check if it is not covered with resin and cloth. It doesn't matter if it is plywood or solid lumber.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Doug fur is known for checking and must be entombed in epoxy and cloth. The selection of non marine lumber makes this decision more so important. If you don't want the checks, then you must use cloth and epoxy. In areas you expect to bash stuff around, like the bilge or lockers, put some cloth and goo there. Don't go nuts with this, just where you need the abrasion resistance. CPES everything and finish her off.

    The Weekender is intended to get folks on the water, cheaply. CPES, epoxy and fancy cloth don't fall into this column. There are lots of these boats around and it has quite a following. Talk with the Stevenson folks on their web site. They'll have taken most every angle to this issue, some going all out with the best materials, others the low buck route, most find a happy place in the middle of their pocket and coat and cloth what they need too, leaving the rest to good upkeep and maintenance.

    No worries, keep at it, have fun . . . Good Luck,
     
  7. gonzo
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    gonzo Senior Member

    Lumber is not marine or not marine. It is graded according to the way it's sawn, knots, splits, how it was dryed, humidity content, amount of sapwood,etc. Plywood has a marine grade.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Excuse my miss speaking about "lumber" it was assumed we all were talking about fur ply (that's DOUGLAS fir plyWOOD - for those that need the additional, abet redundant clarification) and it is a commonly complained about problem (surface checking) with the material.

    Most lumber is graded by the amount of usable yield from each piece.
     
  9. rjmac
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    rjmac Junior Member

    gonzo,

    Lumber is not marine or not marine. It is graded according to the way it's sawn, knots, splits, how it was dryed, humidity content, amount of sapwood,etc. Plywood has a marine grade.

    Yes, at a greater level of detail you can grade the plywood as stated...., it's been a while sence I have looked into the plywood industry grading.... From what I understand, now you can get pressure treated marine plywood, the stuff has a warrenty (cool... :) )

    I kinda took a quick look and found this link.... Thanks, this looks like the direction I will be going.....
    http://www.apawood.org/level_b.cfm?content=app_spe_boat

    ===================================================

    Guest,

    Please excuse me if I seem a little on the brash side, but Par stated makes a good point, it comes down to application, boats in general are very application specific when it comes to building and design.

    Ditto on go for it.....
     
  10. gonzo
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    gonzo Senior Member

    Pressure treated marine plywood is very rot resistant. The problem is that the toxic chemicals that kill fungus kill people too. That is why "green wood" is banned from residencial construction after 2004. I think that for application where it will be covered in fiberglass it will prevent rot and be safe. For example, cockpit soles, transoms and stringers. The FDA bans it in commercial fishing boats anywhere it is in contact with edibles. This includes your catch. The dust of treated lumber is very toxic too. One of the problems, is that the effects are delayed like asbestos. It makes workers careless.
     
  11. rjmac
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    rjmac Junior Member

    Par,

    Please excuse the side slide in the tread....., looks like we just missed each others post by a minute or two... :)

    - I am wondering with a pressure treated lumber, is there a reduction in adhesion to the surface of the lumber (DOUGLAS fir plyWOOD specifically)?
    And would there be enough penatration into the wood, say polyester vs epoxy. This would functionally determine the amount of surface checking that would occur?

    - duluthboats,
    Do you have a website for the resin set paper face MDO...? I would like to learn more about this material...

    - Gonzo, thanks
     
  12. duluthboats
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    duluthboats Senior Dreamer

  13. PAR
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    PAR Yacht Designer/Builder

    I haven't heard of any reports of more or less adhesion to treated lumber or ply. I don't like the stuff personally. It looks to be a lower quality of wood with a good killing agent applied. Finding clear, VG pressure treated stock would be a bear if not only a custom order.

    I would not use polyester on any lumber or ply I'd want to keep for very long. There are way to many home built multi hulls dieing a slow death, in the backyards and marinas across this country, left over from the 70's with their polyester skins hanging off their flanks, to even think about making that mistake again. The jury is long in on how well polyester sticks to wood and it don't. I don't care what anyone will have you believe, no nails sticking up, no staples, no weird hardener ratio mixtures will make the stuff stick well enough to wood compared to epoxy. Who knows what the addition of CCA in treated wood would do to the stickiness of poly, but do you want to risk it?

    Now I know a lot of folks will tell you "we do it up here all the time . . ." and yes, it is done and does work, but only in cases where they are using the wood as a mold for the 'glass hull they lay around it. The north east and the north west is full of work boats that have polyester skins on them. These are thick, massive lay-ups of material that in effect acts as another hull surrounding the wooden one. They even save old worn out wooden hulls with the stuff. Again by putting on so much polyester and cloth that the rotting mass of wood on the other side of it is protected from the moisture by the new shell of a polyester hull. Sort of a cold molding with chemistry.

    The resulting lay-ups for these examples of foolishness are much heavier then should be or need be. In the case of a work boat, a lot could be said for giving the boat another 5-10 years of serviceable use with a skinning of polyester, but a Weekender would not like the addition weight. What would be the point anyway? You might as well build a plastic Weekender as that's what you have once the polyester was thick enough to work as a anti checking coating.

    The only reliable way to stop checks in fur ply is to set cloth in epoxy. Epoxy nor polyester alone has little value in this regard. The cloth is what makes it work in both cases.

    MDO comes in thicknesses from 3/8" and up. It is coated with a rosin paper on one or both sides, primed or unprimed. It is a Doug fur through and through and I believe it has a 1088 rating. I use the stuff all the time and it is great for bulkheads, furniture, etc.

    I've tested gluing face to face and it holds well. I also have an unprimed two sided scrap in a bucket of rain water that has dried out many times in the last year. The paper shows no sign of coming off and has taken on a grayish white look from the light brown it once was. It has taken a slight curved set, while standing in this bucket. The piece is 8" x 24" and is in a 5 gal bucket under a rain gutter down spout. The dogs drink out of this bucket (I have 4 of the beasts) and it is living in a spit and slime covered world. Every so often I have to take it away from one of them as they've run off with it and are teasing one of the other dogs with it. In the summer it's hot as hell here in Florida and we get lots of rain, the bucket is full all the time. In the winter we get near no rain and the bucket gets filled by the hose and filtered well water gets lapped out by the mutts. They prefer the rain water as it has many more critters and crunchies to enjoy then the well water.

    The MDO has be in the sun and rain and several dogs mouths and has held up very well aside from the odd tooth mark or so. We'll see what happens by next year.

    I've never seen it used as planking, but I'd guess it would work well.
     
  14. Armada
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    Armada Junior Member

    I am just starting to build aplywood sailboat and I was planning to fully encapsulate plywood with epoxy and also using cloth on the outer side of the hull. After reading at this forum, it is the first time that I have heard about CPES. I have checked their web site and actually impressed with what they are explaining.
    Q1- Does anybody know how will it react if I first CPES all the plywood and than do the clothing and epoxy of the hull.
    Q2- If the above is ok than what type of paint can be applied to this system.
    Thank you all in advance
     

  15. chandler
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    chandler Senior Member

    Fir ply is the cheapest marine ply you can buy, for a reason. You get what you pay for. Okoume or other mahogany type marine plys will not check if they are coated in epoxy and some sort of U.V. resistant varnish or urethene.
    Fiberglass is not necessary on the the topsides.
    Greenwood,i.e PT, is still sold. They just changed the formula, less arsenic. more copper.
    The problem with most PT is it's made from 20 year old southern yellow pine, all sap wood. Actually the problem with most wood products.
    Marine ply and cdx do not use the same glue. The difference between marine ply and cdx or ac or whatever, is the amount of voids in the plys allowed, and the glue.
    I'd spend the extra buck for okoume encapsulate in epoxy.glass the outside.and make sure it has a good U V protective coating, and maintain that.
     
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