Epoxy coating plywood question?

Discussion in 'Wooden Boat Building and Restoration' started by abosely, Apr 22, 2015.

  1. abosely
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    abosely Senior Member

    Building Wharram Tanenui using System Three & precoating 9mm/3/8" Okoume ply sheets first.

    I'm looking at two options. Either option will be applied in less than 72hrs between coats for the chemical bond. Lightly sanded/scraped as needed.

    1) Use System Three SilverTip Laminating Resin neat. But wonder if I might have to deal with bubbles in first coat.

    2) Use System Three SilverTip Clear Coat Laminating resin for first two coats since it's thinner, may soak in a little more. And from what I understand Since it's thinner the air can get through the Clear Coat Resin easier and won't bubble or at least not as much as the thicker SilverTip Resin.
    It will need two coats to equal one coat of the thicker SilverTip.

    Will use the thicker SilverTip Laminating Resin for all succeeding coats.

    I am NOT thinning down a resin. The Clear Coat Laminating resin is a thinner laminating resin from System Three. I understand the issues with thinning resin, not doing that! :)

    I guess my question is:
    Would there be any downside or issues using the thinner Clear Coat for first two sealing coats on bare ply then using the thicker SilverTip Resin for rest of the build coats, other than one extra coat?

    I would rather apply one more coat and not have to fight bubbles as much.

    Cheers, Allen
     
  2. LP
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    LP Flying Boatman

    Allen.

    Nice project.

    The thinner resin should give you better penetration than the thick which is the better option for your first coat(s). Heating the resin before applying it will also help with penetration. As long as you are not thinning the mix, I don't see a problem with thin v. thick with regard for porosity. If you are able, apply the epoxy on falling temperatures. This causes the plywood to try to draw the epoxy in rather than trying to push out air making bubbles. Once you coat a panel, check on it with in 30 minutes and if you see dry areas, go ahead apply some more goo where it's soaking it in. The first coat is where most, if not all, of the epoxy penetrates the ply so once it kicks, I don't see why you couldn't switch to your thicker resin for your thickness building coats. Thick or thin, if the ply is outgassing, it will try to make bubbles. Stable or cooling temperatures is your best bet for avoiding bubbles.

    72 hours sounds like too long to try to get a molecular bond between coats, unless your temps are really cool. Generally, I've understood the time frame to be with in 24 hours.
     
  3. Canracer
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    Canracer Senior Member

    I agree that 72 hours is sort of to much time to be considered "hot coating." You might be over concerned about the bubbles. Typically that is a cosmetic issue. If you are wetting out sheets of ply, use the thin resin and maybe roll and tip. You can't go wrong.
     
  4. snowbirder

    snowbirder Previous Member

    Allen, i used the same products and okoume ply.

    If you don't want any bubbles, and are working without temperature control, start your coatings at the hottest point of the day. Use a fast hardener. Put all 3 coats on in one day. just wait long enough for the previous coat to transform from liquid to a gel.

    Penetration is not an issue. Don't worry about that. You are encasing wood in plastic, not staining wood.

    Doing it the way you described will mean it'll take 12 years to finish your build. Optimize all steps for speed/efficiency/quality. You can have all 3.
     
  5. PAR
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    PAR Yacht Designer/Builder

    If you don't want out gassing or bubbles from other typically application related reasons, apply the first coat flush with the surface. The idea is to prevent any pools of goo from remaining on it, during the first part of the cure. Once the epoxy has gelled, this concern goes away.

    The simplest method to insure the surface is coated, but doesn't have pools is to smash the goo into the surface with a putty knife, squeegee or plastic applicator. Pour straight goo onto the work and move it around with the knife, pressing down hard and using a very low angle with the blade, so it's reflexive action will help push the wet goo, into the pores of the wood. Once the wood is wet, scrape excess from wet areas to dry areas and smash it in some more. The finished result, once you've got everything wet will have a dull sheen, no pools of epoxy anywhere and some areas will look almost dry (this is normal). Without the pools of epoxy on the surface, there's no place for bubbles to form, so . . .

    When this is cured, a light wash to remove amine and sanding or if still chemically active (12 or less after application, in spite of what suppliers and formulator say, if a structural application) then move on to subsequent coats. These next coats don't need the smash and go technique, as the surface is now sealed and out gassing can't occur, unless working in extreme conditions and temperature swings. Some application techniques make lots of bubbles, such as a roller, so if clear coats are the end result desired, don't use a roller. Even if you're the best roll and tipper, you'll be chasing bubbles with a torch seemingly forever. Use a squeegee and if you must, tip off the edge trails, though most of the time, these will self level.
     
  6. abosely
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    abosely Senior Member

    Thanks Paul, I got the 72hrs for chemical bonding from System Three. Glad to know not to to count on 72hrs.

    My plan is to put 4 coats on the side that will be the interior side, sanded and ready for varnish and 2 or 3 coats on exterior side that will be sheathed with Xynole.

    I'm on Big Island HI so temp is fairly consistent throughout day.

    I thought about putting 4 or 5 sheets of ply that will be coated in one day under tarp 'tent' with a space heater under them and stickers between ply sheets to let warm air circulate some, then as I pull each sheet out to give first coat it will be warm and start cooling as it's coated.
    Still using the method you recommended. Mostly for the side that faces inside.
    Or will it make any difference when using your prescribed method of first coat?

    One other question:
    Would there be any advantage using the thinner Clear Coat Resin for first coat instead of the thicker resin that will be used for the build coats? If not I'll just use the standard SilverTip Laminating Resin for first coat & not have to buy both versions of resin.
    I think the standard SilverTip Resin is a fairly low viscosity resin. But haven't used it yet.

    Cheers, Allen
     
  7. LP
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    LP Flying Boatman

    I wouldn't anything more than a single seal coat with the Xynole. Save your epoxy weave filling and fairing. IMHO.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Epoxy encapsulation is a multi step process. The first step is the sealing coat, which is what I described above. This simply locks down the fibers and seals the pores. There's not enough film thickness to embalm the wood (yet), so the next stage is to bulk up this thickness. If a sheathing is to be applied, you can employ this as the bulking phase, so a sealing coat, than straight to sheathing, knowing you'll apply at least a wetout coat and fill the weave, which provides the film thickness you need for waterproofness. If no sheathing is involved, you'll need two bulking coats, to provide the 10 mils of film thickness (a minimum) for waterproofness. Thinner formulations of goo might require more coats to get the minimum film thickness and I don't bother with these thin versions, for this reason.

    As to precoating raw plywood, I usually don't bother. Cut your parts, then stack them on some saw horses (or whatever) and coat only what you need to. In stead of tenting and using a heater, I'd just use the sun in your area. Cover the plywood pieces with black plastic, of course propping it off the surface a bit. Surround the plywood (I use tarps) with this black plastic and in full tropical sunlight it'll get to 140 degrees under the plastic in no time at all. Even the slowest of hardeners will cure fast like this, but it will also promote outgassing, so pay attention. At 140 degrees, epoxy will cure at 3 to 4 times the speed it does at room temperature, meaning you're sanding and maybe recoating the same day.
     
  9. abosely
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    abosely Senior Member

    Thanks so much for all this help.
    Excellent idea, putting cutout parts under black plastic tarp.

    I apologize for asking so many questions.

    One other question along this theme is about Xynole on the hulls.

    Here in the Hawaiian Islands it is rocky. There can be a nice clear channel right up to beach, but there are some pretty good sized rocks around that huls could end up getting banged into plus rock formations a bit off shore right where the good freediving is. Obviously I will do everything I can to prevent it.

    But getting a hole knocked in hull is more of a concern around here than most places.

    I'm going to sheath the hulls in Xynole for it's abrasion and puncture resistance. The sheathing of hulls is optional and not structural. I know the Xynole is heavier than glass. But still worth it.

    By using Okoume instead of fir or AquaTek Merenti I'm saving some weight, tho it is more expensive. Saving weight there helps compensate for heavier sheathing.

    Question is:
    Would I gain increased puncture resistance if I used two layers of Xynole below water line?

    I'm not really worried about the added weight if it gains me even some more protection from puncture. Not worried
    cosmetic issues but punctures that will let water in the hulls.

    Cheers, Allen
     
  10. snowbirder

    snowbirder Previous Member

    PAR knows way more than me, but I'm curious...

    Why not blast the encapsulation out in one day? I did 5 bulkheads in a day each time for my boat.

    Set them to the side, work on something else during curing process and paint on layer after layer, as one gels, paint on the next layer.

    I can't even imagine sanding bulkheads so many times and not doing everything wet on wet. Why go through so much trouble and effort?

    Mine not only took 1 day for all 5 wooden bulkheads in a given hull, but I only sanded them once. At the very end to make them look pretty and drip free.
     
  11. abosely
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    abosely Senior Member

    Actually that's probably what I'll do on things like bulkheads & such. Sand after all coats are finished & give them a light/thin coat after sanding if I have to sand much.

    I want the panels that show on the inside to be sanded to a fine level of finish. I was a contractor for many years and high end finishing & painting was something I did a lot of. So I want the level of finish work to be the same level that I normally do.
    Plus built custom Aircraft, so I enjoy finishing to a fine finish. Actually I am so used to it once I get a system down it really doesn't take much more work for me to build it to this level.
    I don't mean that arrogantly. It's just I enjoy high level of work. A small run in a panel would drive me nuts! Lol can u say anal retentive! Haha

    The wood working part I'm plenty used to. But the epoxy & finishing of it is new for me. So I gave a lot to learn. All the help and guidance is most appreciated.


    Cheers, Allen
     
  12. PAR
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    PAR Yacht Designer/Builder

    It would be nice to be able to pound everything out in a day, but most don't have this luxury, so mechanical bonds are forced on us. All boats have these types of bonds, so no worries.

    Xynole is great at abrasion resistance, though penetration would be better served with something else, such as Kevlar. Two layers of Xynole will weigh the same as 6 layers of regular 'glass cloth of the same weight, so be careful what you wish for.
     
  13. abosely
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    abosely Senior Member

    I was planning to use 5oz of Kevlar below waterline, at first. But read about possible problems with delamination when combining two different types of cloth.

    Puting Kevlar down first then the Xynole over it since the Kevlar is a pain to fill & fair.

    If there wouldn't be a problem with using one layer of Xynole over Kevlar then I'll use that combination then.

    Will 5oz Plain Style 285 Kevlar take about the same amount of resin as Xynole?

    WIll do both the Kevlar & Xynole while resin is green and use peel ply on both the Kevlar & Xynole to help minimize excess resin and have nice finish on the Kevlar for the Xynole.

    Sorry if I'm giving to much description of process I'm planning to use. Want to make sure I don't use an unwise or incorrect method. As I'm new & learning about working with epoxy & cloth.

    Cheers, Allen
     
  14. PAR
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    PAR Yacht Designer/Builder

    The best location for Kevlar is on the inside of the hull shell, where it can have the most advantage over the impact force. This solves the interlaminate problem.
     

  15. abosely
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    abosely Senior Member

    Ok, excellent. I will do it that way then.

    Again, thanks for all your help.

    Cheers, Allen
     
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