Extruded Polystyrene (XPS)

Discussion in 'Fiberglass and Composite Boat Building' started by gabdab, Sep 12, 2008.

  1. gabdab
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    gabdab Junior Member

    Hi,
    looking at this site I read the builder is using a non conventional type of foam which
    he patiently tested :
    http://www.trinardo.com/y.a.t-yetanothertrinadofoamcompare3

    As he mentions it being fine for small vessels I wonder if doubling the size of his design (42') is still possible.
    Being the price so convenient compared to alternative foams it would really solve some budget problems.
     
  2. rwatson
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    rwatson Senior Member

    He doesnt test for water absorbtion that I can see. This wouldnt matter for a trailer based boat so much, but for 42 feet, it would be a major issue.
     
  3. gabdab
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    gabdab Junior Member

    re:

    I guess you need extensive tests to be safe.
     
  4. rwatson
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    rwatson Senior Member

    are you doing ply or strip plank?

    I found a tech sheet that said there is zero water absorption at
    http://www.finnfoam.fi/client/frontpage//english.pdf

    you could get a small piece and sink it in 20ft fo water for a week. That would give you some usefull info
     
  5. seagull369
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    seagull369 Junior Member

    I wrote the coast guard on the use of prefabbed extruded polystrene sheets (the kind you'd find in Home Depot) for floatation purposes about a year ago. The answer I received was that it's perfectly fine to use for that purpose as long as it does not come in contact with gasoline. This, therefore, would exclude its use within a floor that contains a gas tank.

    I'm not sure what you want to use the stuff for, but if you'd like more info., go to Dow's website below and enter the search "buoyancy"

    http://dow-styrofoam.custhelp.com/
     
  6. zigzag
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    zigzag Junior Member

    Re the high compression foam, I have also investigated possibilities to replace divinicell, Seems the shear strength is much lower in a bending situation, the compressive is however much higher. This however could easily be overcome by inserting some timber stringers or if it is a large deck scenario use notched matrix timber with the foam in the voids. anyone have the time to make some tests?
     
  7. KnottyBuoyz
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    KnottyBuoyz Provocateur & Raconteur

    I've got the time if I could get my hands on some samples. Anybody speak Finnish?

    I'm a little concerned about resins bonding well with this type of foam.

    [​IMG]
     
  8. zigzag
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    zigzag Junior Member

    I did do some quick tests with thin plywood (1/8 ) poplar on either side of the foam. I used gorilla or Purbond single pack PU. the bond to the foam does not need to exceed the shear strength I would opt for some sika flexible PU on the foam and epoxy on the embedded batten. Mike Leneman used standard extruded polystyrene foam on the L7 deck. Might pay to get some feedback.
     
  9. gabdab
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    gabdab Junior Member

    re

    Not sure yet..

    http://www.surfersteve.com/polystyrene.htm

    In this page there is a link to xps usage in surfboards making .. preatty price for :
    $46 for a 8'x4'x3" sheet

     
  10. gabdab
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    gabdab Junior Member

  11. naturewaterboy
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    naturewaterboy Steel Drum Tuner

    You can't take a design and just scale it up, or you may find you and your crew swimming back to shore:eek: :eek: :eek: . There's a little (no, there's a LOT) more to designing a boat than that.
     
  12. gabdab
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    gabdab Junior Member

    Yes, I am little concerned about resizing a design.
    I saw a post somewhere on this forum about it .






    Wikipedia mentions the coast guard having built a 6 person raft in xps in the '40s .
    That must be preatty big as size.
     
  13. gabdab
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    gabdab Junior Member

    re

    Reply from Finnfoam.
    Should I use the skin on non skin type :

     
  14. pcfithian
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    pcfithian Junior Member

    I recently built the cuddy roof for my Tolman out of 1" XPS foam with a 1/8" exterior luan skin on either side, making a foam sandwich. The attached pictures show the foam layer and also the upper skin. It also shows the support bows made from 2 layers of 1/2" plywood at the front, middle, and back.

    I used 3M's Fastbond 30 water based contact cement. I found this method to be fast, low cost, and strong. The roof is incredibly stiff. The advantage of using contact cement is that no vacuum bagging or clamping is required, only a laminate roller to ensure adequate contact between the foam and the skin as shown.

    The sides showing the exposed foam edges will be scraped back 1/2" or so and filled with a wood flour/epoxy filler, then faired and glassed over, reducing shear load on the foam.
     

    Attached Files:


  15. rwatson
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    rwatson Senior Member

    What does
    "Special Note When bonding wood veneers, success is dependent on many variables such as
    environmental conditions, bonding process, type of base material, type of veneer,
    adhesive type and top coat finishing systems to name a few. For un-backed wood
    veneers, water based contact adhesives are not recommended.
    It is the user’s
    responsibility to thoroughly test any adhesive for its suitability in bonding wood
    veneers. It is also recommended to follow the veneer manufacturers
    recommendation and industry guidelines."

    What does "unbacked" mean ?
     
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