Neglected Kells 23 sailboat... advice sought

Discussion in 'Boatbuilding' started by retrosub, Jun 10, 2014.

  1. PAR
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    PAR Yacht Designer/Builder

    The penetrating epoxy is nearly useless on a plywood build, so save it for the few things it's effective with. Any good quality solid species will do, to treat the edges of plywood. I use several of the pines, oak is common, as is mahogany or other "pretty" species. This assumes it'll be encapsulated with the rest of the plywood. When using this treatment, I usually rabbit or spine the solid wood piece to the plywood. This machining operation offers a mechanical lock as well as the glue line. If the piece is pre-installed, like yours, then a 45 will do, say with a router and straight edge guide, though I'd still be inclined to use a straight cut like a rabbet or simply butt the new solid wood to the edge for decorative purposes, if only to make things simple. On an exposed bulkhead opening, such as a companionway cutout, I'll spine the solid wood onto the plywood edge, so abuse can be absorbed a bit better.

    Another option is simply to "band" it with a veneer, along the end grain of the plywood. They sell iron on and glue on strips just for this, but I usually make my own by ripping lengths on a table saw, surface planing them down to thickness and gluing them on.

    Lastly, a guy I know that builds work boats uses extruded aluminum "T" bar stock on his plywood edges. He mills a grove for one leg of the T and glues the aluminum stock into it. He then lightly radius's the aluminum, until it's flush with the plywood faces. This makes a tough, clean edge on the end grain that doesn't have to have special finish requirements.
     
  2. retrosub
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    retrosub Junior Member

    Two questions:

    1) What is penetrating epoxy good for? I was going to use it on all bare plywood before painting, and on any bare wood I wanted for character. Bad idea? Is regular epoxy better?

    2) The inside of the hull look like crap, big globs of epoxy, gaps, exposed fiberglass weave and such. Glassing over this will use a lot of epoxy and just create more bubbles. Sanding would be a major pain. I was thinking to knock down the high spots and then fill the gaps to the same level. Can I fill this area with Bondo? Then I would put thin plywood or biax fabric over the top of it.
     

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  3. missinginaction
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    missinginaction Senior Member

    There are two schools on the CPES (penetrating epoxy). I'd agree with PAR and say that it's pretty much worthless. That said when I was doing a recent restoration I early on found that bare plywood tended to soak up an initial coat of general purpose resin at different rates. This gave the coated piece a mottled appearance that needed a fair amount of sanding to get fair.

    I found a product from System Three called Clear Coat. This is a low viscosity 100% solids resin. It doesn't smell of any solvents. I'm no chemist, but I found the Clear Coat useful as an initial coat over bare plywood. After the Clear Coat was applied I soon after coated with 2-3 coats of General Purpose resin to get a good chemical bond. The reason for the Clear Coat was to simply get a stable base for the General Purpose resin. It saved me some time sanding.

    As far as the poor fiberglass work on the inside of the hull.....

    Can you see it once the boat is finished? If yes why not remove some of the globs and exposed fiberglass with a grinder and then just coat with some thickened resin? If it's not visible I wouldn't worry about it too much. Keep in mind that it's easy to overthink these projects. You want to do a good job but you can get old fussing over things that don't really make a material difference.

    http://www.systemthree.com/reslibrary/tds/Clear_Coat_TDS.pdf
    http://www.systemthree.com/reslibrary/tds/SYS3_TDS.pdf

    The technical data sheet links are listed above. You'll notice that in terms of mechanical properties the Clear Coat is quite similar to the General Purpose resin.

    MIA
     
  4. Mclennon1001
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    Mclennon1001 Junior Member

    Have you used this systemthree with good results?
     
  5. retrosub
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    retrosub Junior Member

    I'm not going to get fussy on any of it, see the crude butt block instead of a scarf or splice. That said, I do need to cover the bottom with another layer of glass or wood because it's so uneven and crappy it'll collect dirt and such. That's why I'm thinking bondo. Of course I'll use the grinder liberally on the high spots, but that still leaves a lot of depressions which would be expensive to fill with thickened epoxy.
     
  6. SukiSolo
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    SukiSolo Senior Member

    Actually I would sand a fair bit, with random orbit and Multitool (Fein). To fill the hollows an epoxy mixed with microballoons is much better than 'bondo' which I understand to be polyester automotive body filler. I don't think we use that term this side of the Pond. Bondo has no inherent strength. The epoxy has more integral strength and will allow fast fairing and smoothing which you can then paint.

    Preference would be a 2K epoxy primer, say 2 coats then something on top to suit. Depends on the wallet and performance you want here.
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Bondo (polyester filler) doesn't stick to epoxy well ,ditto wood or pretty much most of the surfaces used on a boat. If it's a powerboat the vibration will "shake" out the Bondo in short order. I don't recommend it's use anywhere in the marine environment.

    The penetrating epoxy subject can get convoluted, without some understanding of what it is and what it does, which most simply just don't know. There are uses for it, but with well established epoxying techniques, it's usefulness can be dubious at best. The System Three stuff is a good example as well as the regular resin from RAKA. Both are much lower in viscosity than the usual resin choices, for situations that require it, such as prime coats. This said, if regular viscosity resins are used with a proper technique, penetrating epoxy and low viscosity resins are unnecessary.

    The first coat on any raw wood will be blotchy to some degree, if you just apply it topically. This is because of density differences between the winter and summer growth portions of the wood, natural resin content in the surface, etc. Most importantly it's because the epoxy was applied topically and left to stand (dry). All that's required is another coat and the surface will be sealed. On the other hand if you use the "mash and scrape" application technique (see my Tips & Tricks link below), the whole surface after the first application on raw wood will look pretty much the same. You'll still need more coats, to bulk up film thickness, but you'll start with a level(er) playing field.

    To get back to your questions. To smooth up the inside of the hull, where the polyester and roving was applied, you'll want to use a filler, not a thin epoxy. Once the resin system (regardless of type) has cured, you're not going to saturate it any more. This means you're simply filling dents, holes and distortions on the surface only. For this use a modestly thickened mixture of cosmetic filler. Vertical and overhead area will require a non-sagging mixture of course. Use Q-Cells and/or micro balloons, talc and a pinch of silica to control viscosity. Smear this all over the roving and let cure, knowing you'll sand much of it off, smoothing things out. It may require multiple coats (it will) to get things really smooth. Most of the time these areas are left rough like this because it's out of sight, so consider the effort required in these areas, as it's a pain in the *** to sand smooth in some locations.
     
  8. missinginaction
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    missinginaction Senior Member

    Ive used many gallons of System Three over the years. That's not a knock on other manufacturers, but System Three has for me one big advantage.

    A 2:1 mixing ratio.

    Can you see how it's really hard to screw that up? Also, it's to easy mix a really small amount, say an ounce and still get it right in a little mixing cup.

    As for the bondo, I'd say this. I personally won't even use bondo on a car let alone my boat.

    Look at it this way. If you were going to do this 100 times it might be worthwhile to try and cut a corner here and there to save some money. In this case you're doing one boat. How much money will you save? Epoxy, properly applied over polyester resin sticks like the dickens. It's waterproof, relatively easy to work with and doesn't stink of styrene. Stay with epoxy, you'll be happier in the long run.
     

  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    There are quite a few 2:1 epoxies. Marinepoxy from Bateau.com is 2:1 at 1/2 the price of System Three.
     
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