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Thread: One detail of stitch & glue method

  1. #1
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    Default One detail of stitch & glue method

    Hi folks,

    I have seen many times that people cover with epoxy the interior of the plywood boat (see for example Wharram designs or Chesapeake Light Craft boats).

    I remember that one friend of mine told me that never ever encapsulate plywood with epoxy. The interior should be covered with linseed oil or varnish to let the wood "to breathe", otherwise it will rot very soon.
    Does it make sense? Please comment.


    kind regards,
    Igor

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    Default Re: One detail of stitch & glue method

    Mirror Dinghy kit instructions say that coating both sides of the plywood with epoxy is the way to go. Plywood core rot is the most common cause of Mirror dinghy deaths.
    In Germany, fibreglassing over wooden boats is often referred to as a "Leichentuch" (burial shroud).
    How soon rot sets in will depend on how good the epoxy coating has penetrated the outer plywood layers. Microcracking can occur as the plywood flexes, allowing water to seep in. If the boats are stored in dry environments, they may dry out between uses but on the long run, rot can win.
    Personally I have been varnishing over my brightwork (clear varnished) surfaces with a flexible oil-based varnish regularly, although the boat was built with the epoxied (or perhaps polyestered) panels. I had rot in a wooden part that had been epoxy (or polyester, I didn't build it) coated and looked perfectly sound under the varnish because the resin-soaked surface wood does not rot. A millimetre deeper, the whole piece of mahogany was soft and my shroud plate screws pulled out in a light breeze one day and the mast fell overboard!
    When I started repairs, I found that the gunwale and a section of the hull had serious rot.

  3. #3
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    Default Re: One detail of stitch & glue method

    I dare say that the glue between the veneers is fairly impermeable, so the ply may not breathe much. Sealing the edges is vital.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: One detail of stitch & glue method

    it do make sense, an oil on the inside, letitbreath thing
    on the other hand it do not, na mix product.

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    Default Re: One detail of stitch & glue method

    I remember that one friend of mine told me that never ever encapsulate plywood with epoxy. The interior should be covered with linseed oil or varnish to let the wood "to breathe", otherwise it will rot very soon.
    Does it make sense? Please comment.
    Gee, there are some folks who might have more experience than your friend when it comes to building epoxy-coated plywood boats (by a factor of a hundred or so) who would disagree with your buddy. They're called the Gougeon Brothers and they invented and prototyped much of the current epoxy boatbuilding technology. Personally, I don't consider linseed oil a finish at all. You might as well leave the wood bare. At least that way it won't turn black.

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    Default Re: One detail of stitch & glue method

    Boatbuilder and designer Thomas Firth Jones (who sailed over 50,000 miles on his plywood boats) once wrote something to the effect that he'd "rather paint a boat with ketchup than with epoxy". He liked epoxy fine for glue and fiberglass work but was dead set against encapsulating wood. He recommended painting what wasn't glassed with a good quality semi-gloss, exterior latex or one of the newer paints, but not the old oil-based stuff.

    I use latex paint on what isn't glassed myself, got tired of everything I used linseed and turps on turning black and needing constant attention to look good. It breathes well enough, apparently.

    I sure do agree with sealing the ply edges as best you can though!

    The Gougeon Brothers have come up with some neat stuff sure but please remember where they get their money - Selling epoxy! Of course they want you to slather yer boat, inside and out, from stem to stern with as much of it as you can afford.


    Frankly, for a small open boat that doesn't live in the water, I don't imagine it makes all that much of a difference one way or the other.

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    Default Re: One detail of stitch & glue method

    As Nick said above, the glue between the veneers is airtight. As for wood "breathing" every single product we traditionally put on it is designed to slow and hopefully stop the water absorption from the atmosphere. Linseed oil oxidizes into a polymer forming a waterproof barrier (aka. Linoleum), the problem is it does it very slowly so we try to speed it up with dryers. Paints and varnishes are just a better version of this, as is epoxy, they all form a more or less impermeable film over the wood.

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    Default Re: One detail of stitch & glue method

    Standard practice these days is to seal the ply inside and out with epoxy and glass the outside. Many designs - especially for kayaks and other lightly built boats - call for glass inside and out. Once the ply is encased between two layers of glass, it becomes a wood core that adds some stiffness to the structure but never gets wet or needs to breathe. As Todd points out, the Gougeon Brothers did engineering studies about this stuff for decades and their book is still the bible on this type of construction. You can read it here.
    -Dave

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    Default Re: One detail of stitch & glue method

    The whole idea of plywood "breathing" is a joke. Plywood is either (1) sealed or (2) in the process of deteriorating from moisture absorption. It doesn't soak up humidity or moisture and then breathe it out and return to a perfect state of hunky-dory-ism. That moisture is most likely going to do at least some damage to it. Repeat the process often enough and the damage will eventually start to take its toll. The question then becomes how much moisture are you going to live with? The edges are going to contain a whole lot of end grain, just waiting to soak up water, so you had better spare no amount of effort to really seal them as permanently as is humanly possible. Face veneers could get epoxy, various kinds of paint or varnish, or oil products as long as they are maintained. That's going to be the key though, because as soon as their resistance to moisture penetration starts to diminish, wood damage will start. In the case of oil finishes, by the time it starts to look like it needs a fresh coat it is already later than was ideal.

  10. #10
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    Default Re: One detail of stitch & glue method

    Quote Originally Posted by 62816inBerlin View Post
    Mirror Dinghy kit instructions say that coating both sides of the plywood with epoxy is the way to go. Plywood core rot is the most common cause of Mirror dinghy deaths.
    In Germany, fibreglassing over wooden boats is often referred to as a "Leichentuch" (burial shroud).
    How soon rot sets in will depend on how good the epoxy coating has penetrated the outer plywood layers. Microcracking can occur as the plywood flexes, allowing water to seep in. If the boats are stored in dry environments, they may dry out between uses but on the long run, rot can win.
    Personally I have been varnishing over my brightwork (clear varnished) surfaces with a flexible oil-based varnish regularly, although the boat was built with the epoxied (or perhaps polyestered) panels. I had rot in a wooden part that had been epoxy (or polyester, I didn't build it) coated and looked perfectly sound under the varnish because the resin-soaked surface wood does not rot. A millimetre deeper, the whole piece of mahogany was soft and my shroud plate screws pulled out in a light breeze one day and the mast fell overboard!
    When I started repairs, I found that the gunwale and a section of the hull had serious rot.
    I've been told (but have not verified it myself) that the Mirror kits were supplied with polyester resin. From what I've read poly is not the best sealant. My only experience with it was my first Mirror (I didn't build it) which had significant rot. Everything I've used actual epoxy on has held up quite well. I hope that continues to be the case as my current build is a CLC Skerry which will be fully encapsulated...with epoxy...polyester never to be seen.

  11. #11
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    Default Re: One detail of stitch & glue method

    Oil, paint, epoxy...it's wood covered with a water impermeable coating.

    Of course you could leave it bare. It gets wet then dries quick...provided water doesn't pool. But rain water from the sky or just condensation will usually gravitate to the bilge and stay there unless the boat also is angled to flow it out the drain and ventilated.

    Most wood that stays wet allows fungus to grow and then decay. With the exception of the most durable hardwoods, timber like Elm for instance that positively loves to be covered with water, alot of the most durable timbers don't glue so well, move alot with changes in moisture or are just plain heavy to use for small boat construction.

    So most people add a covering. Of that list oil is the easiest to apply, epoxy is the most durable. That's the deal. An owner knowing what he's chosen will likely keep up the necessary maintenance whichever.

    The issue with the most impermeable durable coating, epoxy, is that if small cracks open up- its flexible but only upto a point (say the boat is beating to windward hard etc) then water will wick into the crack and be held there underneath by the unbudging epoxy covering, continued dampness will ensue and rot begin.

    So there's an argument that looser less durable coatings shed quicker can help the boat equilibriate but they will need repeat application. Is it a wash? Some people think so. Others favour epoxy coating. Others slap on a coat of Decks oil instead yearly or keep up with the paint. A decent breathable cover and ventilation will be a factor irrespective of the coating.

    It needs thought and a look at the boat. Areas where a bit of movement might occur and spell curtains, water getting into the garboard for instance, might be better with a small epoxy fillet to reinforce the inside lap and keep water off the plies. With plywood you have end grain that can wick moisture all the way through between the plies. Certainly most people would favour epoxy coating the lap edges to prevent this. Though I've seen oil finished boats that have been fine.

    If you left a series of glued ply construction boats open out in the sun, the one built form durable materials, two thick epoxy coats then covered in 2 pack white paint would hold up the longest. Not everyone enjoys epoxy coating or using two pack paints though...and it's supposed to be fun, not every boat always need to be an airloom or might be a quick and dirty boat for a purpose.

    It will be a question of what's best for the boat, but also what do you like doing, applying or the smell of! There's no right and wrong, just a personal choice, but a choice that you live with. I'd also add that most people have periods in their life when they are too busy or engaged with other life events that the boat gets left for a bit. A boat that can take care of itself for a while is good to come back to.
    Last edited by Edward Pearson; 09-16-2022 at 05:25 AM.

  12. #12
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    Default Re: One detail of stitch & glue method

    Epoxy is crap . . . . as a paint.
    It needs to be filled with something, glass fibers, Dynel, pigment. Glass flakes are the best. Then it does become durable and impermeable.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: One detail of stitch & glue method

    Epoxy is not crap as a paint Nick. Harder to apply, more expensive I accept. Neither is it necessary in most instances, or an end in itself, even when it is chosen for it's usefullness.

    This stems from early epoxy use books suggesting " glue with epoxy, paint with paint"

    Since then we know epoxy is also a very usefull covering, besides preventing water penetrating into wood, it also gives a more stable covering for subsequent paint finishes.

    As a primary coating it is stronger, more impermeable, soaks in further, and is more durable than a one pack paint.

    Taken to extreme, fully immersed GRP boats with osmotic blistering, get recoated in epoxy resin not 'painted' below the waterline.

    Epoxy laminates last longer before blistering than vinylester before polyester (the most used still) even with grp boats.

    Down the line of ownership, most boats end up neglected. At that point the boat has to fend for itself. My money would be on the epoxy coated boat beneath a two pack finish to survive longest. It's just a more stinky, more costly and more time consuming to apply and finish well, but then you're set for a while.

    Some two pack paints aren't more costly than one pack and go straight on the epoxy without undercoat, Jotun paints that are used for comemercial stuff are like that. Dad epoxied his spars then two pack Jotun and never touched them. My oiled/ spar varnished single pack International spars look a million dollars but ding and scuff at a moments notice. Beautifull and that's what I wanted, but low maintenace they won't be. Single pack paint n varnish just not as strong and tuff. Convenient though it is. You can probably cut the cost and unpleasantness down by epoxying upto the turn of the bilge in small boats and have most of the benefits.

    Most epoxy isn't used in boatbuilding or even as an adhesive, it's used by industry to coat and seal the inside of metal food cans.
    Last edited by Edward Pearson; 09-16-2022 at 07:01 AM.

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    Default Re: One detail of stitch & glue method

    Quote Originally Posted by Etdbob View Post
    Boatbuilder and designer Thomas Firth Jones (who sailed over 50,000 miles on his plywood boats) once wrote something to the effect that he'd "rather paint a boat with ketchup than with epoxy". He liked epoxy fine for glue and fiberglass work but was dead set against encapsulating wood. He recommended painting what wasn't glassed with a good quality semi-gloss, exterior latex or one of the newer paints, but not the old oil-based stuff.

    I use latex paint on what isn't glassed myself, got tired of everything I used linseed and turps on turning black and needing constant attention to look good. It breathes well enough, apparently.

    I sure do agree with sealing the ply edges as best you can though!

    The Gougeon Brothers have come up with some neat stuff sure but please remember where they get their money - Selling epoxy! Of course they want you to slather yer boat, inside and out, from stem to stern with as much of it as you can afford.


    Frankly, for a small open boat that doesn't live in the water, I don't imagine it makes all that much of a difference one way or the other.
    50,000 miles..pffffft ..hold my beer

    epoxy is the BEST thing to cover wood with
    the epoxy must be covered of course, but there is no better primer/sealer.
    none

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    Default Re: One detail of stitch & glue method

    My Eastport pram is over 10 yrs old, epoxy coated on both sides, and no rot yet.

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    Default Re: One detail of stitch & glue method

    Quote Originally Posted by Edward Pearson View Post
    Epoxy is not crap as a paint Nick. Harder to apply, more expensive I accept. Neither is it necessary in most instances, or an end in itself, even when it is chosen for it's usefullness.

    This stems from early epoxy use books suggesting " glue with epoxy, paint with paint"

    .
    No, it is based on an engineering knowledge of what makes paint work.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: One detail of stitch & glue method

    Quote Originally Posted by Hugh MacD View Post
    I've been told (but have not verified it myself) that the Mirror kits were supplied with polyester resin. From what I've read poly is not the best sealant. My only experience with it was my first Mirror (I didn't build it) which had significant rot. Everything I've used actual epoxy on has held up quite well. I hope that continues to be the case as my current build is a CLC Skerry which will be fully encapsulated...with epoxy...polyester never to be seen.
    Absolutely true that Mirror kits were supplied with polyester resin.Until the late 1970's epoxy was hard to find and expensive.Now it can be found almost everywhere and its still expensive.

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    Default Re: One detail of stitch & glue method

    Thank all of you for your answers and a link to a book of Gougeon Brothers (I didn't know about it!). For small boats I would agree that epoxing inside and outside is fine especially if the boat is not permanently in the water. I did it for my Wood Duck 10 kayak (from CLC) just as was suggested in the manual.

    For bigger boats I am doubting. I like the look of bare wood, so I was thinking about transparent varnishes, based on natural components. See for example dutch website Houtolie? deCokerije maakt natuurlijke oliŽn! (hout-olie.nl)). (natural oils for wood). I met them during a wooden boat building festival in The Netherlands.

    As far as I remember, that friend of mine (from Ukraine) insistently was telling me that if the boat got slightly damaged from outside, the water seeps inside and finds no escape route which causes rot. He gave me as an example a story about two guys who built a plywood sailboat which rotted in a few years because they had covered inside with epoxy.
    Back in Ukraine people are using mostly plywood (FSF-type) based on birch tree veneers (heavier than okoume). Maybe this makes a difference ? and/or perhaps a local climate is the reason?


    kind regards,
    Igor

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    Default Re: One detail of stitch & glue method

    Yes it is true if an epoxified vessel gets damaged on the outside, water can get sucked in and do damage.
    That is why we fix em when they break.
    I recon there are many many more plywood boats that have not rotted out because they were resinated inside.
    and yes, birch has poor rot resistance,so it's a poor choice for a bigger boat, one that does not live on a trailer under cover.
    bruce

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    Default Re: One detail of stitch & glue method

    Quote Originally Posted by Igor S. View Post
    For bigger boats I am doubting.
    You can doubt all you like, it won't change the facts.

    Quote Originally Posted by Igor S. View Post
    As far as I remember, that friend of mine (from Ukraine) insistently was telling me that if the boat got slightly damaged from outside, the water seeps inside and finds no escape route which causes rot.

    Water and water vapor doesn't migrate transversly trough plywood, there is plastic between the wood layers. It's absolutely irrelevant what's on the face veneers, if water finds its way inside plywood it will rot.

    Quote Originally Posted by Igor S. View Post
    Back in Ukraine people are using mostly plywood (FSF-type) based on birch tree veneers (heavier than okoume). Maybe this makes a difference ? and/or perhaps a local climate is the reason?
    Okoume is in exactly the same category as birch when it comes to rot resistance, the lowest.

  21. #21
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    Default Re: One detail of stitch & glue method

    if the boat got slightly damaged from outside, the water seeps inside and finds no escape route which causes rot. He gave me as an example a story about two guys who built a plywood sailboat which rotted in a few years because they had covered inside with epoxy.
    The whole concept of the interior unsealed plywood forming an "escape route" is a load of crap. It is far more likely in real life to form an entrance route. Perhaps the two guys who built the plywood sailboat that rotted out didn't know what they were doing in the first place. The use of epoxy does not automatically guarantee that your boat won't rot. You have to use it properly, which has, by now, been quite well documented and proven by real world experience with hundreds of boats. Before you start believing stories that some guy told you about some other guys you might want to get a lot more actual information about the case. Otherwise, you are just spreading unsubstantiated rumors with no personal experience to back it up.

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    Default Re: One detail of stitch & glue method

    I built a 14' 'stripper' scow back some 50 years ago. Used lumberyard exterior ply & polyester resin, locally sourced clear FOHC redwood (you could find that back then!!) for the strips, bronze boat nails to hold strips onto frames until the 'glass & resin went on (inside & out), two-part resorcinol glued strips edge to edge & frames.

    We all make mistakes, right? We all can learn from those, both our own and of others, right?

    Stored outdoors, usually upright on a trailer year-round (too heavy & wide to flip), usually covered, that boat lasted about eight years until the frames rotted enough to be noticed. This was fresh-water only, in Chicago suburb's climate conditions.

    My second 'build' is a CLC Waterlust kit, finished & launched a year ago. Epoxy appears to be much more sturdy stuff for both structural purposes as well as encapsulating everything organic in the build. She's painted (Kirby's) inside & out, stored on trailer in a garage when not being used, hoisted up near the garage's ceiling during the off-season, upside down.

    My expectation is that when it's time for me to part ways with this project she'll leave her next owner pleased with how I put things together. Time will tell.

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