Paint under/over epoxy

Discussion in 'Strippers, Stitch-n-Glue, and Other Wood Composite' started by erbinsky, Dec 30, 2007.

  1. erbinsky

    erbinsky Canoeist/Builder

    Hi all. Hope everyone had a great Christmas.I have a week off work and started my project for this winter,a 12 ft. rowing/sailing skiff.I'm at the point of putting the decks on and have a question about the next step ,glassing the hull. I have built numerous cedar strip canoes and one s&g canoe so I have some experience with fiberglass.For this boat I had to join 1/2 a sheet of marine plywood (Okoume) to a full sheet to end up with the 12 feet I needed.The inside of the cockpit will be painted so the joint is not a problem. I would really like to leave the outside of the hull natural and cover it with varnish but my scarf joints are really quite ugly.I would like to paint over just the joints but I'm afraid of poor adhesion of the epoxy if I paint before I glass.I'm also afraid of the paint bleeding into the vanish if I paint on top of the epoxy. My last option is to paint last but agian will it stick to varnish. Any coments would be greatly appreiciated. Thanks and Happy New Year!... Jeff
     
  2. Todd Bradshaw

    Todd Bradshaw Sailmaker

    Epoxy over paint can only stick and seal as well as the paint, which is far less than the epoxy can do on bare wood - so you don't want to paint first. Painting last, over the varnish is no problem as long as you sand the varnish where you want the paint to be before painting. Most enamel manufacturers want the surface sanded to somewhere in the 80-150 grit range to give the surface enough "tooth" for the paint to stick well.

    You can also varnish over paint after scuff-sanding the paint but remember that varnish tends to yellow with age. Even with spray equipment it's quite difficult to get the varnish perfectly even. As it then ages over a solid opaque color, you may start to get an uneven, splotchy effect due to the varnish thickness variations (don't ask me how I know this). In any case, as long as the resin is cured (probably a week or more) and the paint or varnish used are allowed to dry for a few days before you add something on top of them, color-bleeding of any combination should not be a problem.

    I suppose you could color the areas before glassing using pigmented epoxy, but it's a much more complex job than painting later. Most opaque resin pigments (including black, white and mixing powders like graphite or aluminum) take two or three thin coats minimum before they start looking even and truly opaque. I suspect that finishing the glass work, then varnishing the boat and finally lightly sanding, masking and applying a couple coats of enamel to the areas you want to cover would be the best way to go.

    Without knowing exactly what you need to cover, would veneer strips or small "overlays" be a possibility? It's possible to buy very thin sheets of veneer from woodworking supply places like Woodcraft - real wood, sanded on both sides and only about as thick as a business card (not the iron-on or cloth-backed veneer strips from the big box stores). You can glue the veneer down to the bare plywood over the joints with epoxy or wood glue and then fiberglass right over it. The stuff is so thin that the level change will disappear in the fiberglassing, filler coats and final fairing stages. You do need a means of holding the veneer down tight and flat while the glue cures, but some handywrap, a scrap of plywood and some weights or clamps will usually do the trick. As long as the veneer winds up down tight to the surface of the ply it will actually strengthen the scarf as well.

    I don't have any photos of a boat project done that way, but I built a mandolin for my brother a couple years ago and veneered the top with some super-thin curly maple, set in WEST epoxy resin and then top coated with more resin and varnished (didn't need the strength of fiberglass, so plain resin was used). The first photo shows the veneered and coated surface. The veneer was glued down, allowed to cure and then sanded smooth (random orbit, 100 grit) and epoxy coated. These resin filler coats were then sanded flat (photo#2). Finally, it got about fifteen coats of sprayed varnish which was later block-sanded up to 12,000 grit and buffed by hand (probably a bit much for boat varnish...) - photo#3

    The veneer is reasonably cheap and kind of fun to work with. It might offer an opportunity to do more than just cover the scarfs.
     

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  3. woodenkayakguy

    woodenkayakguy LOVES Wooden Canoes

    When I was finishing my 13' millcreek my roomate who used to refinish old furniture suggested shading lacquer,this is basically a powder that is mixed in lacquer then sprayed on when the lacquer evaporates the powder is left,then just epoxy or varnish over top,we used this on all the edges and faded it into the main part of the boat to give it an antique look and hid all the imperfections on all the joints
    [​IMG]
     
  4. Todd Bradshaw

    Todd Bradshaw Sailmaker

    Lacquer doesn't evaporate away, but lacquer thinner does. You can mix powdered dyes with laquer thinner and make sprayable transparent shading solutions (the same sort of thing as alcohol-based stains, which can later be overcoated with epoxy. However, if your shading laquer actually uses lacquer for the vehicle to carry the color, then overcoating it with epoxy is pretty risky. Layers of other materials between wood and epoxy, or between layers of epoxy tend to create a much weaker bond between those layers, making them more prone to flaking, peeling, chipping, delaminating etc.
     
  5. woodenkayakguy

    woodenkayakguy LOVES Wooden Canoes

    Thanks for the correction todd. The boat was epoxied then shading lacquer(with lacquer thinner)then varnished
     
  6. Tim

    Tim New Member

    Erbinsky:
    I had the same problem with a 14' Tom Hill design ultralight. My scarf joints weren't pretty. Plus, as much as I love natural wood, I find Okoume plywood about as interesting as a flat slab mahogany door. I went ahead and painted and I'm really happy with the results.

    I had no trouble painting over epoxy. Sand first, like Todd suggested, but don't forget the primer. Paint sticks best to primer and good primer can stick to almost anything. I used good quality latex primer and an oil based marine enamel and it's still there years later.

    Tim
     
  7. Todd Bradshaw

    Todd Bradshaw Sailmaker

    I'll disagree with that one. Tests (done by Gougeon Brothers, etc.) have shown that primer does not affect the adhesion of decent quality enamels to properly prepared epoxy. The paints stick and last just as well when painted straight over the sanded resin. There is nothing in primer that would make it any more adhesive than the ingredients in the paint. What primers do often contain are fillers which are fairly soft and which sand easily and feather out easily and smoothly (some marine primers even contain microballoons). If you have small surface irregularities to fill and fair before painting, removing them by sanding primer is easier than from the harder resin below. On the other hand, the faired resin would make a harder, tougher base.

    But do not expect primer to stick any better than paint would as it does not and generally contains nothing that would make it do so. If you have paint adhesion problems over sanded epoxy there is something else doing it - improper prep, contamination or the wrong kind of paint.

    Interlux Brightside Enamel painted directly over barrier-coating of sanded WEST Epoxy. Two coats, rolled on and tipped out with a brush out in the driveway. At the time of this photo, the paint job was two years old and had been sitting outside year-round and in the water on a mooring the entire previous summer. It was in for pre-season clean-up and anti-fouling paint touch-up on the bottom. We don't need no stinking primer!
     

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  8. Tim

    Tim New Member

    Can't argue with results like that. Beautiful.
     
  9. OP
    erbinsky

    erbinsky Canoeist/Builder

    I went with the veneer idea. It looks beautifull on one side...the other side we don't talk about.The hardest part is getting it to lay flat.If you get any kind of a high spot that gets sanded when you are smoothing out the epoxy you end up with colour variations or worse yet plywood showing through.Aside from this I'm really happy with the way it turned out.If I could figure out how to post pictures I would. This is going to be my last project for a while because in addition to my full time , 44 hour a week job my wife and I just bought a small restaraunt business. Happy paddling everyone...cheers ...Jeff
     

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