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Thread: Durability of expanded PVC foam board in exterior application

  1. #1
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    Default Durability of expanded PVC foam board in exterior application

    Hello - new member. Hope this post is OK - the boat is not wooden, but the question relates to marine application that is traditionally wood, and I thought this is where I could find knowledgeable responses.

    The nose board in my 16' Achilles inflatable's floor rotted out, after 35 years. It was originally probably 9 or 10mm 5-ply plywood, fully encased in fiberglass, though inexplicably one thin strip where the board sits in the aluminum channel that locks it to the next piece, was left unglassed, which is probably why it rotted finally. In looking to find suitable replacement plywood - 1/2" is too thick, 3/8" too thin, and quality marine or exterior plywood seems unavailable anywhere locally I've looked - I've begun to consider expanded PVC foam. I can get 1/2" Komatex at the local TAP Plastics for half the price of King Starboard. It should be fairly easy to shape and fit to the channel.

    The manufacturer only rates it for limited external use, though they have a similar product, Komacel, they recommend, but I haven't been able to get a satisfactory answer as to what the issue with Komatex might be. I only need a 2'x3' piece, and ordering the Komacel online would be too costly. I've seen other discussions online of PVC foam board for external non-structural use, so I'm wondering if anyone might have any thoughts about this application.

    The board is mostly a place holder - at most it sees very mild compression force in preventing the main boards from shifting forward, though in the nearly two seasons since the original piece began to disintegrate, I haven't seen much sign anything is moving. It bears no direct weight of any magnitude. It only needs to hold it's shape, and not fall apart with infrequent and transient water exposure.

    Mike

  2. #2
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    Default Re: Durability of expanded PVC foam board in exterior application

    MacBeath Hardwoods has Meranti and possibly other marine ply in half sheets, well worth the cost. You could also probably use any decent quality plywood and glass it, as I can't imagine that inflatable lasting another 20 years, so the longevity of marine ply may not be needed.

    https://www.macbeath.com/
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  3. #3
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    Default Re: Durability of expanded PVC foam board in exterior application

    if the inflatable is 35 years old. Any plywood sealed with epoxy or even paint will out last the life of the dinghy.

  4. #4
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    Default Re: Durability of expanded PVC foam board in exterior application

    It is amazingly old, isn't it? I'm thinking there may be something blessed. The seams simply never show signs of separation, even the transom bonds look solid. I keep it out of the sun and heat as best I can.

    Anyway, I went to MacBeath yesterday but got there too late - never having been there, it looked pretty bereft of product from the outside. I'll check again, hope they're not going out of business.

    Thanks, I take your points about longevity - does that extend to using interior grade as well? There seem to be many more choices there, some quite high quality in appearance - no/voids especially, and solid lamination - and the exterior stuff I see is all very rough.

    If I go with 1/2" of the more normal sort (not MacBeath hardwood), I probably have to router off .050 or a little more from the faces for the section of edge that fits in the channel, before glassing. I've seen 3-ply birch with maybe 1/8" thick outer plies, and up to 7-ply stuff in another type that would probably mean wiping out the surface ply on one or both sides. Does one approach sound preferable to the other?

  5. #5
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    Default Re: Durability of expanded PVC foam board in exterior application

    I can't see any sort of foam standing up for more than a season.

    What about a 3/8 interior with a coat of dynel & epoxy? Should outlast the dinghy & be about the right thickness. The epoxy should eliminate any weather issues.
    "If it ain't broke, you're not trying." - Red Green

  6. #6
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    Default Re: Durability of expanded PVC foam board in exterior application

    An inflatable boat, 35 years old, that is astonishing! I'd have thought even if hardly used the seams would deteriorate over time.

  7. #7
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    Default Re: Durability of expanded PVC foam board in exterior application

    The manufacturer's website says Komacel can be used outdoors http://www.kommerlingusa.com/outdoor.cfml

    The skin will be robust. The foam core will be your weakness, some of them go crumbly when exposed to UV ... but some cores are just as durable as the skin.

    To me it looks like a cladding product that will have enough strength to span between cladding rails so it could be strong enough for your description of a small panel without significant loading. Although why not get the slightly too small ply and coat it with epoxy to waterproof it and also build the thicknesses for a snug fit?

    IMHO if you are worried about durability, consider the what-if scenario if it fail. If you're a long way offshore and it would let in enough water to sink you'd have a problem. On the other hand, if failure happens close to shore on an inland waterway and you have enough reserve buoyancy to make it home then you'll be OK .

  8. #8
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    Default Re: Durability of expanded PVC foam board in exterior application

    Other pvc board products like Azek hold up well in exterior building uses.
    Its worth a try.

  9. #9
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    Default Re: Durability of expanded PVC foam board in exterior application

    We have always stored our Avon Red Start inflatable in a dark part of our garage when we are not using it as a shore boat. As a result, this boat that is now nearly forty years old, is still in good condition! We make a point of renewing the varnish on the floor boards whenever they start to show signs of wear. "HAGGIS" is still is in good shape as he does not spend extended periods of time exposed to the weather. I think the fact that the floor boards are not allowed to have water soak into the end grain has a lot to do with their good condition. Were they to begin to break down, I would opt to make or by new ones of the same material as were the old ones.
    Jay

  10. #10
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    Default Re: Durability of expanded PVC foam board in exterior application

    If 1/2" is too thick, and 3/8" too thin, can you just add or remove material (depending on which ply is chosen) where the measurement is critical? then glass the lot.
    There is nothing quite as permanent as a good temporary repair.

  11. #11
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    Default Re: Durability of expanded PVC foam board in exterior application

    40 years! Wow! Jay I am convinced now my view of inflatables, which was previously rather dim, requires some reassessment. Thanks for opening my eyes.

  12. #12
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    Default Re: Durability of expanded PVC foam board in exterior application

    The durability of this boat has amazed me as well. I had read of eventual seam problems with glued hypalon boats, and had owned both older hypalon and PVC inflatables where the transom to fabric gluing eventually failed massively. This one even at 36 years shows nary a sign of any glued fabric seams lifting or leaking. Rubber handles have rotted, D-ring pads have had to be tacked back down, but the tube construction is still solid. Leaks seem primarily through the valves. The transom glue joints still lie flat and show no delamination that I can see either, but that doesn't mean those joints haven't weakened I suppose. It's stored typically covered, and with a scaffolding to keep the tarp off the tubes, to stay cooler.

    Not knowing much about plywood, I didn't know if I could take the router to the clamp insertion strip on a 1/2" board, without causing problems. I've seen decent looking 5 ply exterior, and 7 ply interior grade, where there'd still be at least 3 or more plies left after the worst case scenario for routering. Lowe's has 1/2 birch with really thick faces, but only 3-ply. At the handful of yards I've visited, I haven't seen any 3/8 that didn't look like crap. I haven't found any place yet with 3/8 marine.

    When I saw the Komatex, I thought it might be the quickest solution, and it's locally available in custom per sq ft pricing. Not that there's no good plywood solution at hand, but if I can spend a half hour shaping a piece of foam board, that seemed preferable to the trouble of breaking out the fiberglass mess. I've only done a bit of fiberglassing, so it's still a challenge. I hadn't thought of epoxying the Komatex for weatherability - I'll check about compatibility. If I have to slim it a bit from 1/2" to fit the channel, it would be good to be able to treat the surface. The Komatex is not as obviously skinned as some other expanded foam PVC that I've seen, it appears pretty homogeneous.

    I'm going to check a couple more lumber yards this week, and visit another plastics place across the Bay, then decide which way to go.

  13. #13
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    Default Re: Durability of expanded PVC foam board in exterior application

    Do you know why your current inflatable is lasting better than other experiences? Is it different glue, or different fabric maybe?

    I think any of the ply options will work. Machine it, or build it up by gluing on anything (wood, ply veneer, glass, whatever)... all of that is just about getting the fit right, but durability will come from sealing it. Paint it with epoxy for a really good job, but even just regular paint (even house paint) or varnish will work provided you've used enough coats to prevent water reaching the wood. Worst case scenario, if you try something which falls apart after a few years, what does it matter if it didn't cost much in the first place, you can try again with the benefit of experience gained in the first attempt.

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