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Thread: Finishing and Maintaining Plywood Boats?

  1. #1
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    May 2009
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    Default Finishing and Maintaining Plywood Boats?

    Evening All

    I thought about posting this in http://forum.woodenboat.com/showthre...-Skiff-Reports but considered that a new thread might be appropriate. In that thread, John Welsford advocated a full paint job as opposed to epoxy coating plwood boats. In view of the ever increasing cost of BS1088 marine plywood, some builders are using cheaper but still WBP glued plywood in their builds. My questions are about the initial finishing and subsequent maintenance of these builds and I would be grateful for any views fellow forumites may have.


    1. I've heard that the use of a specialist epoxy sealer is better than coating with a general purpose resin since the elasticity of the sealer more closely matches that of the wood thereby avoiding (hopefully) the damage caused by a sharp impact as John descibes.
    2. Some dispense with epoxy sealing entirely and advocate the use of epoxy primer paint for the same reasons as 1 above followed by undercoating and two top coats.
    3. Back in the mid 60's when my late Father was building a Mirror dinghy #3129, the instructions said to paint the inside of the bouyancy tanks with primer only as the use of gloss paint in these in encourage condensation to form leading to rot. Is this true that only flat or statin finish paints should be used here? BTW, Mirror#3129 lasted well until it was destroyed during the Great Storm of 87.
    4. If a full paint marine system is used, is the use of a metallic primer, eg Al, to be prefered over a normal type.
    5. As always, a little TLC given often is better than major refurbishment.

    Kind Regards

    Nick

  2. #2
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    Default Re: Finishing and Maintaining Plywood Boats?

    question #1 - "specialty sealers" - The best way to think of these things is the fact that structurally, they are quite inferior to real epoxy resin in just about any and every category that counts. They can make for a decent primer for a paint job, but that's about the only use I can find for them. Hit a boat hard enough with something sharp and any epoxy product (or paint, as well as the wood itself) will be damaged and need repair to prevent water intrusion. There is also a lot of BS being posted lately about flexible epoxy resins. Unfortunately, the people posting it, and those reading the posts and repeating it, don't know squat about what the stuff is actually good for. It certainly does have some uses and can be a great product, but on wooden boat constructions the standard resins are usually going to be your best bet by far, and flexible epoxy should be reserved for a few specialized situations (many of which most builders will probably never encounter). If you don't want to damage your wooden boat with sharp objects - avoid them. If you do damage it, fix it and don't wait around too long to get to it. There is no magic protective ingredient that's damage-proof.

    (2) "Epoxy paint" - There are several different types available (even stuff for repainting your refrigerator) and many of them have precious little epoxy in them at all. They may be a bit harder than some other paints, but don't confuse their ability to seal wood or their durability with that of epoxy resin. It's paint.

    (3) buoyancy tanks these days are better off being sealed with at least two coats of real epoxy resin. Paint (any paint, gloss, flat or satin) doesn't even come close. Even with resin, it's a pretty good idea to put some sort of access plate on float tanks if there is room. It's also sometimes handy for repair access if you happen to hit one of those dreaded sharp objects.

    (4) I don't know much about metallic primers. I generally stick with whatever primer the paint manufacturer suggests. They know a hell of a lot more about their paint than we do and it is in their best interest to give you the best, most durable paint job possible (so that you will become a return customer). I don't, however, prime over properly-sanded epoxy resin. If that's what the boat happens to be coated with and it's free of defects needing filling, you're not likely to find a better painting surface for most enamels. There is certainly nothing at all wrong with using a traditional paint/primer job, free of any high-tech epoxy coatings on a plywood boat, as long as it's good plywood (ideally non-fir) and it's well done and maintained. If you hit something with the boat, fix it before the next outing. The advantage to adding epoxy resin or epoxy mixed with certain fillers. like graphite, or epoxy with fiberglass or other fabrics to the picture is that in the long run, they may substantially limit wear and tear on the hull from normal activities and epoxy resin is going to be the best sealer you will find for keeping water out of the plywood.

  3. #3
    Join Date
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    Default Re: Finishing and Maintaining Plywood Boats?

    I second everything Todd says and will second the point about sealing with epoxy resin (like tanks, etc.) but would really suggest choosing a resin designed for coating. There are a few ways these are better than general purpose, like West System or System Three General Purpose. Instead go to System 3's website. They have an entire section on laminating and coating. These guys make epoxy for specific purposes and maximize the properties for that use. All my plywood gets sealed nowadays with Laminating Resin and/or Clear Coat. They form an incredible base for paint making the paint job last a long time. I figure 10 years at least before I need to do a new paint job. Just touch up each year and repair any gouges asap, like Todd, said.

    I think an all paint job is a good way to go too, and have done it on all my boats up to now, but I think eventually plywood checks enough that the paint comes off even on a good wood like Sapele marine plywood. The epoxy coating significantly reduces this effect. Michael Strorer's first Goat Island Skiff is 15 years old almost, was well coated with epoxy, properly sanded and thoroughly painted, and apparently it looks like new and has yet to receive a fresh new paint job.

    With all that said, I do not epoxy seal all my timbers, like gunwales and seats. I choose good wood and use a paint/vrnish system that lets the wood breath. Specifically, I use the linseed oil paints and varnishes on timbers where convenient (e.g., gunwales, seats/thwarts, spars, floorboards, oars).

    This thread is a good one to refer to as well

    http://forum.woodenboat.com/showthre...=encapsulation
    Clinton B. Chase
    Portland, Maine

    http://tinyurl.com/myboats

  4. #4
    Join Date
    May 2009
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    Default Re: Finishing and Maintaining Plywood Boats?

    Todd, Clint,

    Thanks for your advice. I was particularly interested by Clint's remarks on laminating resin and/or clear coat. As far as possible, I would like to avoid epoxies with large quantities of solvent in them like CPES or the like. Doing some research on the web I came across this product http://www.connexiontechnology.co.uk...k-wood-mk2.pdf . It seems to have had good reports. Otherwise, it will be whatever GP resin (WEST, MAS, SP etc) the chandlers has on offer.

    As regards an all paint job it would be the usual 6 coats of Primcon followed by undercoat and two of enamel. Unfortunately, the old standby primer I used to use (International UCP - Universal Clear Primer) is no longer available as is it's counterpart Blake's Woodseal (Elf 'n' Safety and all that!!!).

    Regards

    Nick

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