Waterproofing Epoxy or Polyester & Fiberglassing Question?

Discussion in 'Boatbuilding' started by dukbutr, Jul 29, 2012.

  1. dukbutr
    Joined: Jul 2012
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    dukbutr New Member

    I am new to boat building, so bare with me on my lack of knowledge for fiberglassing. I have read a lot of do's & don'ts on this subject, but i am not sure what products to use to waterproof the frame work of the inside of the boat before I install the plywood & start the fiberglass. Everyone has there own opinions on this, I'm just looking for what best suits my needs. I am building a Kara style Layout boat that is 14' long & 44" at it's widest, so my questions are:

    1) What type of epoxy or polyester will waterproof the frame, & give some structural strength? This boat will get wet inside & out so it needs to be watertite.
    2) What are the differences in polyester & epoxy resins, as I see there are both being used in boats, surfboards, & other water sports products....Pros & cons?

    Any advice is welcomed.
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Polyester will not waterproof wood. Don't listen to anyone that suggests it will, because they're talking out their butt and can't be taken seriously. There's no debate on this subject among professionals.

    What type of boat are you building, as generally, the inside of the boat is the side you want to stay dry. Now, I do understand some types of boats, like drift boats for example will get wet a little, but getting splashed is way different then getting immersed and soaked.

    If you want the bullet proof, waterproof setup, then it's epoxy encapsulation for everything. Not just a epoxy coating but full encapsulation, which will insure the wood stays dry, stable and un-wet. Most boats don't need this. The hull needs to be waterproof, the planking, decks etc., but most can live with just painted interior surfaces.

    As to polyester, well this is a product developed initially for production builders, who are interested in the cheapest, fastest method to pop boats out of a mold. It's fine for a surf board or a Bayliner, but it absolutely sucks on wood and isn't waterproof (which is why it sucks on wood). So, if you want to pop out a few dozen parts or boats from a mold, in the next few weeks, well polyester is the stuff you want. Ten years from now, you'll call someone like me to fix the rotten plywood transom core or rotted out wooden stringers in your boat, but hey, you got them popped out and sold, so what would you care at that point. Polyester has it's place, but in one off boat building, there are better choices, epoxy being the hands down preferred goo to use.

    Welcome to the forum Dukbutr. Do they have water in big piles in Kansas? :)
     
  3. sean-nós
    Joined: May 2010
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    sean-nós Senior Member

    I encapsulate all the timber on my build with west system epoxy just leaving the parts that have to glued yet bare, I also coated it in a few coats of varnish for uv protection.

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  4. BPL
    Joined: Dec 2011
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    BPL Senior Member

    Your boat looks gorgeous!!
     
  5. dukbutr
    Joined: Jul 2012
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    dukbutr New Member

    Par....
    Even though were are in a severe drought here in the mid-west, we still have some water. I'm planning to use, marinepoxy resin to seal the frame & plywood inside & out. This boat I'm building is similar to a Pirogue for you boys down south, it will get a lot of water on the inside & out. Due to getting in & out of it a lot, which will bring water inside the boat. I still have to build a transom do some sanding & filling on some more gaps, before I can go any further. But I need to order my epoxy, so I just wanted to here from someone who has used the material than a company testimonial.
     
  6. PAR
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    PAR Yacht Designer/Builder

    Joel over at Bateau.com (the place that sells Marinepoxy) is a good guy and builds the boats too. He's got plenty of experience and Marinepoxy works well. If you buy direct, instead of through some of their vendors (Ductworks, etc.) you can save a little money.

    If you plan on encapsulation, you'd be well advised to read the tutorials and watch the videos over there as well. Remember encapsulation is just as the word suggests and every screw hole, notch, cutout, side and especially end grain needs epoxy. 3 coats is the minimum for waterproof. If the surface is to be covered with fabric, apply 2 coats then the fabric, as the fabric wet out coat will serve as the third.
     
  7. dukbutr
    Joined: Jul 2012
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    dukbutr New Member

    Par, thanks for your input, I will try to update as I go through the process.
     
  8. pauloman
    Joined: Jun 2010
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    pauloman Epoxy Vendor

    the problem is that wood expands and contracts with moisture while everything else (including paints and coatings) expand and contract with temperature. So to keep a coating intact (and encapsulating the wood) it needs a really good bond and a bit of flex or give. Epoxies with its big molecules essentially just bond to the surface of the wood. The use of solvents with all sorts of coatings, will penetrate a little bit into the wood and produce a better bond. So the best products are high solvent coatings (like an mcu), or even solvent added to epoxy or spar varnish (multiple coats of any of them) - best of course is using solvent free epoxy and fiberglass cloth - the cloth providing the resistance to expansion, smoothing out the bonding and other stress forces etc. and completely encapsulate the wood.

    It is very similar to 'what to do to keep plywood from checking' and you can see how it is a hard question to answer unless you go with the epoxy and glass.

    paul oman
    progressive epoxy polymers inc
     
  9. rwatson
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    rwatson Senior Member


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

    All of the testing data, including my own has concluded the same thing. Though solvents can improve penetration, it's not the penetration that's important, in regard to waterproofing, but the quality of the coating. Most formulations of laminating epoxy have sufficient enough elongation properties, to handle the physical dimensional changes in encapsulated wood. Non-encapsulated wood is a different story and solvent based coatings can offer an advantage, but this also means you're not using epoxy to is full potential and frankly, you might be better off with a wholly different coating approach, such as alkyds or polyurethanes.
     
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