Extruded Polystyrene Billets

Discussion in 'Materials' started by MamaChicago, May 29, 2022.

  1. MamaChicago
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    MamaChicago Junior Member

    I need to source Extruded Polystyrene blocks to replace those that used to be inside the hull of a vintage 1965 Alcort Sunfish. I can’t find a source for less than $300, and that is without shipping costs.

    I need approx 20” x 10” x 8 feet.

    Any recommendations for a way to find this less expensively? The blocks provide structural support, so I absolutely have to either replace them or figure out a different way to support the thin fiberglass deck. I’m interested in any creative suggestions that would keep the boat light but still give a rigid support to the deck.
     
  2. bajansailor
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    bajansailor Marine Surveyor

    Welcome to the Forum Mama.

    Would it be feasible / possible to use a two part 'pour' foam that expands within the hull to fill the whole space after it has been poured in?
     
  3. MamaChicago
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    MamaChicago Junior Member

    I’d love to do that, but I think the price would be prohibitive.
     
  4. bajansailor
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    bajansailor Marine Surveyor

  5. MamaChicago
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    MamaChicago Junior Member

    I’m going to backpedal a little…. I love the idea of this, but I’m also worried about what would happen if I do crack the hull. I’m realizing that my patching options become significantly reduced. Maybe what I need to do is make a mold and pour new blocks from this stuff.
     
  6. bajansailor
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    bajansailor Marine Surveyor

    If you do this, then I presume that you would have to take the deck off in order to install the blocks?
    I think that it is a relatively simple flanged joint re the hull / deck connection on a Sunfish, so this might not be too difficult?
    And if you do this, then you could pour your foam into the void space, and trim any excess away to suit afterwards, prior to reattaching the deck (?)
     
  7. fallguy
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    fallguy Senior Member

    In addition to taking it apart, there are ingress holes. On youtube, a guy uses a vacuum in reverse to find the holes. Those would get patched, then use new pour foam. Some other youtuber posted a video drying out a boat, but 'believe me' when I tell you; not possible. If you just do the foam; it will all resaturate overtime.
     
  8. MamaChicago
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    MamaChicago Junior Member

    Agreed. Because there are no blocks at all under the deck right now, I really see no choice other than splitting the deck, bow and stern, and placing the foam blocks in the original layout. I’ll just use more of the same foam to adhere them in place in the hull. I have
    Three inspection ports that will allow me to add foam at the connection between deck and blocks after I re-seal the seam.
     
    Last edited: May 31, 2022
  9. Rumars
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    Rumars Senior Member

    Buy normal XPS for house insulation, glue the slabs together with thickened epoxy or PU glue. Price is what it is, insulation is cheapest.
     
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  10. upchurchmr
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    upchurchmr Senior Member

    +1 for Rumars suggestion.
    Pour foam will just get soaked relatively quickly.
     
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  11. fallguy
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    fallguy Senior Member

    A vendor I use did a saturation test on pour foam and the results were disappointing and did not meet the datasheets. We recommend coating pour foam cuts with epoxy.
     
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  12. MamaChicago
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    MamaChicago Junior Member

    Very helpful to know! Thank you.
     
  13. MamaChicago
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    MamaChicago Junior Member

    Off to Home Depot in the morning. Given the thoughts on pourable float foam becoming a sponge, I have once again reconsidered!
     
  14. fallguy
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    fallguy Senior Member

    The pink foam does better than the white stuff. White beaded foam will get wet overtime; impossible to dry. Me, I'd use the pour foam after leak detection and repair. I'd avoid cutting pour foam without the epoxy seal.

    If the leaks were repairable without taking the deck off, I'd just install deck plates and then pour the foam slowly through those.

    my 2 cents
     
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  15. gonzo
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    gonzo Senior Member

    Extruded polystyrene is a closed cell foam rated for underground installation. It is relatively cheap and easy to work with. The color is usually pink or light blue.
     
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