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Thread: First time builder - S&G dinghy questions

  1. #1
    Join Date
    Oct 2016
    Location
    London, United Kingdom
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    11

    Default First time builder - S&G dinghy questions

    Hi all,

    I've gotten to this stage with my Simplicity 8 dinghy build and have a few questions.



    1. Should the entire inside of the dinghy be coated with epoxy before painting?
    2. Should the inaccessible buoyancy compartments be coated in epoxy/paint before sealing.
    3. Should the inaccessible buoyancy compartments be filled with some form of foam? If so, what type?
    4. Should the exterior of the boat, where not covered by glass fibre may be coated in epoxy before painting.
    5. More of a general question related to the above - I'm using West System 105 resin with 205 Fast Hardener. Although I warm both the resin and hardener before use, it is very viscous when applied to fibreglass/plywood and ends up going on very thick. I'm applying it in temperatures of around 15 degrees centigrade and although the substrate has not been warmed, it's also not particularly cold. My workshop has no power so I have no way to heating the atmosphere or the boat. It appears to me from watching videos online that the mixed epoxy other people are using is much less viscous and can be easily brushed on. Except for temperature, am I doing anything else wrong?

    Thanks in advance. I could really use a bit of guidance!

  2. #2
    Join Date
    Apr 2015
    Location
    St. Helens, Oregon
    Posts
    1,509

    Default Re: First time builder - S&G dinghy questions

    Welcome aboard, Monzu. Nice looking build so far You'll find a lot of variation here on full epoxy encapsulation VS paint, but I'm of the "Coat It" crowd. Every surface, inside and out. For the first coat of epoxy I like to spread it not with a roller, but with a scraper. Work it in to the pores and get as thin a coat as possible. Then, once cured, sand that and do another, slightly thicker coat. Alternately, you might just coat everything with CPES (which I haven't tried yet...but I definitely will!) and then paint. I haven't worked much with the 205 (I use the slower hardener usually...but I'm usually working in warmer weather) so I can't speak to the thickness. Usually the 206 is thin enough you can roll and tip it, but it still goes on pretty thick if rolled. Great for 2nd coats, but I prefer a scraper for that first coat. The extra thin coat takes longer to cure, however...the very thin reaction mass slows down the process. Nice sawhorses, by the way!

  3. #3
    Join Date
    Oct 2010
    Location
    Central Vermont
    Posts
    339

    Default Re: First time builder - S&G dinghy questions

    Hi Monzu - As Hugh predicted, here is a different opinion. On my Lightning, the two most respected Lightning builders advised against fully encapsulating the boat. Back in the 1960s, Nickels & Holman built their wooden Lightnings with 3 coats of epoxy on the outside and only clear sealer and varnish on the inside, and that is what I did. A good number of those boats are still on the water and doing well.

    The theory of encapsulation is OK but in practice it is very hard to seal every little thing. And, it is also very difficult to find every little ding that has broken the epoxy layer and is letting moisture get inside where it will be trapped and lead to rot. Using sealer and varnish on the inside allows the wood to breath and allows moisture to escape if it comes in the from the outside.

    On the other hand . . . I varnished the entire inside of my boat and have promised myself I will never do that again. I find varnish finicky and frustrating, and doing the inside, with sanding between each coat, took forever and wore me out, both physically and mentally. Next time I do the inside, it will be paint, except for maybe the trim and the seats.

    So I would do 3 coats of epoxy on the outside and paint on the inside.

  4. #4
    Join Date
    Jan 2004
    Location
    Norwich,United Kingdom
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    6,045

    Default Re: First time builder - S&G dinghy questions

    I would definitely coat all surfaces inside the buoyancy tanks,paint or other coating would be OK.I wouldn't put foam in them and inspection hatches are a good thing.

  5. #5
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    15,639

    Default Re: First time builder - S&G dinghy questions

    Wow that is a heavily built 8 ‘er!
    will she be abused as a tender or handled and stored carefully?
    How you build an epoxy boat with no power?

  6. #6
    Join Date
    Oct 2016
    Location
    London, United Kingdom
    Posts
    11

    Default Re: First time builder - S&G dinghy questions

    Thanks for the all the responses. Really useful.

    She will serve as a tender so will receive a certain amount of abuse, but should be maintained fairly well.

    The boat is a bit overbuilt as I wanted to install buoyancy tanks and got a bit carried away with the hardwood trim (I found a huge stack of 2x4 sapele in a skip).

  7. #7
    Join Date
    Feb 2006
    Location
    Pennsylvania
    Posts
    8,350

    Default Re: First time builder - S&G dinghy questions

    I'm with the coat it inside and out crowd, but I don't see the value of laying the epoxy on thick if it's going to have paint as well. As to the flotation compartments, you don't want foam in there. It would just trap moisture. Foam is for open, ventilated spaces. But do add an inspection hatch of some sort so you can check that it's staying dry in there, and also use the space to store small stuff. I see you have one installed in the center compartment already.
    -Dave

  8. #8
    Join Date
    Oct 2009
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    Default Re: First time builder - S&G dinghy questions

    CPES the inside, then epoxy coating,like Interlux 2000 or Interlux404/414
    I leave the inside of my 2dingys with just the epoxy coating on the inside. It does not get dusty as a one part undercoating would. I add a small dollop of paint for coloration. Blue for her,brown for him .
    The boat looks like an Ocoume ply, so I might lean to putting dynel on the outside bottom.

    Same epoxy coating as above for the outside, then a few thin coats of a brush able two part LP.
    ....this is how I do mine, our el toro is nearly 40 years old, and she takes licks most days.
    bruce

  9. #9
    Join Date
    Dec 2012
    Location
    Providence, RI USA
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    1,458

    Default Re: First time builder - S&G dinghy questions

    The slow hardener is a lot thinner. easier to brush, but...

    I would coat everything, inside and out with CPES, then paint.

    Nice dinghy!

    Mike
    "near it, a small whale-boat, painted red and blue, the delight of the king's old age."

  10. #10
    Join Date
    Nov 2008
    Location
    tacoma washington
    Posts
    1,073

    Default Re: First time builder - S&G dinghy questions

    I wouldn't warm up the epoxy. that speeds up the cure time...might sound good but, you want the epoxy to penetrate as deeply as possible. before it fires off. I don't know what your shop temps are, but I've always found it best that I apply such coatings at a low temperatures , allowing you to enjoy a slightly relaxed pace of work. after I'm done, I turn up the thermostat to achieve a reasonable over night curing of the epoxy. By the way your boat looks great!
    Last edited by the_gr8t_waldo; 03-12-2019 at 12:45 PM.

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