Epoxy Encapsulation and Varnish

Discussion in 'Wooden Boat Building and Restoration' started by MastMonkey, Aug 23, 2010.

  1. MastMonkey
    Joined: Oct 2009
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    MastMonkey Junior Member

    If I am coating the exterior of a hull with epoxy that I will later varnish is it still necessary to use a grain sealer? The hull is constructed of marine grade Philippine Mahogany ply.
     
  2. Homefront
    Joined: Oct 2009
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    Location: Eastern Pa

    Homefront Junior Member

    No.

    Multiple (at least 3) coats of epoxy will fill the grain. Be sure to sand well enough to remove drip marks and imperfections, then use 2-3 coats of a good marine varnish with U.V. additives to keep the epoxy from suffering U.V. degradation.
     
  3. apex1

    apex1 Guest

    Homefront is right, but...

    take care you buy UV PROTECTING varnish. UV resistant is NOT sufficient, it means the varnish itself can stand UV rays but does not protect the Ep coat.

    We apply the second coat of neat Ep while the first one is still "green", means not cured. Then let cure and sand before applying the third (sometimes fourth) coat. Sand again before varnishing.
    If the surface is still not even after 4 layers of Ep, use a clear filler (PU) before you varnish. It may take several coats of filler to get a perfect result. You have to sand between the filler coats when it has to be showroom quality. And in that case you will need up to 20 and more coats of varnish, each sanded, going from 240 to 2000 grit.

    Regards
    Richard
     
  4. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    I'm sure others will weigh in here but I don't think that this is a good idea.

    Here's the problem. You're coating with epoxy, which is subject to UV degredation. OK, you cover with varnish, but varnish is relatively soft AND varnish tends to wear away from the effects of the sun as well as abrasion and just knocking around.

    So, as you use your boat you're going to have to be:

    1: Hyper attentive to any damage/failure of the varnish.
    2. Willing to varnish the boat on a regular basis to keep the epoxy intact.

    or:

    3. You're going to miss something, which will cause failure of the epoxy from UV or impact damage.

    The solution?

    Why not just varnish the hull and leave the epoxy out of the equation?
    or, better yet

    Use epoxy with a layer of fiberglass cloth to give the hull some resistance to impact damage and then paint the boat with a good quality marine paint. I personally have had great results with the two part polyurethanes such as Interlux Perfection or Alwgrip.

    Varnish is fine above the waterline if you're willing to maintain it, but for the hull of a boat I wouldn't think of it.

    Good Luck,

    MIA

    BTW, if you do decide to pursue your original idea of varnish over epoxy be sure to check for compatability. Many times varnish will take a looong time to dry over epoxy unless it's specifically made for use with the epoxy that you decide to use.
     
  5. alan white
    Joined: Mar 2007
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    alan white Senior Member

    I agree with MIA. The epoxy plays an active role in sealing the hull and risking exposure of the epoxy to UV rays means the future possability of a massive amount of labor to repair. I have never personally cared to show the world my boat was made of wood (or loved the look so much that I'd pay such a premium) though I can understand it might be very important to some people.
    You have to weigh the cost of maintainance against the advantages, which are never practical but always aesthetic considerations.
    Know that you will need many many varnish coats---- possibly 12 initially. and at least two more each season PLUS immediate repair of equal thickness over any nicks or scrapes during the season (at least for keeping the surface looking even and newish).
    No, I wouldn't do it. White paint, even single part, will last a few years and then will just need a single coat of paint to look new again.
    Varnish over epoxy will always look older over time to some extent.
     
  6. MastMonkey
    Joined: Oct 2009
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    MastMonkey Junior Member

    I may have to rethink this and determinine how important my original conception of the boat is. I really wanted to show that it is a wooden boat. It is a small boat and I am not completely concerned with being "showroom" quality, but I do want a nice finish. I had varnished a few pieces and really liked the way they looked, but I didn't do nearly that much work, only several coats over sealed wood. I am also trying to be economical which makes just painting the boat a much more practical alternative.

    But, I really want to show the wood...

    What would be the merits between these options:

    1. Only applying the epoxy below the waterline and fiberglassing the bottom and varnishing the rest.

    2. Epoxy over the exterior of the hull and marine paint.

    3. Skipping the epoxy and fiberglass completely and just giving the wood the best finish I can with grain sealer and varnish.

    Though my preference asthetically is for the varnished wood would the finish make the boat much less durable than with the epoxy encapsulation? I see the epoxy as being a sort of additional barrier between the wood and water given damage to the finish. The boat is not going to live in the water and will be sheltered when not in use, so maybe I am making too much work for myself?
     
  7. apex1

    apex1 Guest

    I concur in general with MIA and Alan, but bear in mind that glass and epoxy makes for a much better abrasion resistance and watertightness than varnish.

    I would strongly recommend to glass the entire hull outside (using Epoxy), when the boat sees some rough useage.
    Inside I always recommend paint. It is just a PITA to sand the inside of a hull, and varnished surfaces have to be coated after a while.

    And yes it is less durable without epoxy encapsulation. Much less.

    Your option 1 is not a good idea.
    Option 2 is a question of taste, not longevity or other technical issues.
    Option 3 is done quite often when the boat is hauled after every trip, but one has to touch up every single scratch immediately.

    Is it a canoe?
     
  8. MastMonkey
    Joined: Oct 2009
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    MastMonkey Junior Member

    It is an outrigger sailing canoe 24ft long. Thanks for the tip about UV Protection versus Resistant. I did not know that, but fortunately the varnish I had already bought is of the protection kind. I think I am pretty certain I will epoxy the entire exterior now, having thought about it. I have been sticking with the plan of building it to be robust and durable so I think I should stick with that. I have to check the price for glassing the entire exterior. The minimum I was planning was the bottom and a few inches up the side from the flat bottom.

    The boat is marine ply but I am going to try laying a cedar strip deck. I might end up doing a combination of both: varnishing only certain parts like the deck and gunnels to show the wood and painting the rest.

    Thanks again for your help. I am not quite at the stage yet to be doing it, but it is coming up and this gives me lots to think about.
     
  9. John Riddle
    Joined: Aug 2008
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    Location: Vermilion, Ohio

    John Riddle Junior Member

    MM:

    I do a fair amount of work restoring cold-molded Thistles to competitive racing condition so I have at least a 20 year history with varnish over epoxy in the type of application and use you will see. We always encapsulate with epoxy, inside and out, using pretty much the method Apex described. The outsides are almost always sheathed in glass - mostly because the glass does a better job preventing print-thru at the veneer glue lines than epoxy alone does. Not sure why but that's our experience.

    I have only experienced a long varnish cure-time once when I didn't allow the underlying epoxy to fully cure in cool temperature before varnishing over it. Since then, I provide plenty of cure time before I varnish.

    I finish sand the epoxy with 180 grit dry and apply at least 4 varnish coats with the understanding that at least 2 fresh coats will be applied each year to maintain the UV protective quality of the varnish. That system works with the Epifanes varnish we use. You may need more coats with some other lower-solids varnishes - you'll have to judge that. High wear areas get more attention as needed. The important thing is to keep the varnish in good shape so the underlying epoxy stays in good shape.

    That method works in the Thistle class where the boats are dry-sailed and completely covered when they're not sailing. I'm guessing your boat will be too. If not, and it's exposed to UV full-time, especially in more southern climates, I would double the initial varnish coats. In either case, before the maintenance coats, I give it a hard sanding with 180 -220 grit to remove what I think of as the "dead" layer (the varnish at the surface that I assume is degraded by UV and no longer protecting). If your boat is exposed full time, especially in the south, I'd also consider doubling the coats of yearly varnish or revarnishing more often.
     
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  10. MastMonkey
    Joined: Oct 2009
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    Location: Cali

    MastMonkey Junior Member

    John:

    Thanks for the input. It is boats like the ones you have on your webpage that made me really want a varnished finished finish. They are lovely. It makes me want to stick too my original plan despite the added effort. I think I am going to go for it. I had originally intended to have this boat done before the end of summer but since that isn't going to happen I figure I have the time, why not make this boat really shine.
     
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