Expanded Polystyrene Foam

Discussion in 'Fiberglass and Composite Boat Building' started by eyes, Apr 30, 2007.

  1. eyes
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    eyes Junior Member

    I've also found out that KNOWN boatbuilders here are meeting the US Coastguard requirements using the right materials.
    I saw the Expanded Polystyrene Foam being used in some repairs they told me.
     
  2. Phx1967
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    Phx1967 New Member

    If it is under the boat floor sealed between the outer stringers it would not be exposed to gas or oil. therefore it would work I believe
     
  3. Ike
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    Ike Senior Member

    I am retired Coast Guard and spent over 20 years working in the Office of Boating, with boat manufacturers, and for a long time ran the Coast Guard's flotation testing program.
    First: you are misintrepreting the regulations. The flotation standard is a performance standard. That means that the boat must perform in a certain way when tested for flotation. I won't get in to the actual requirements. You can see them written in plain English here Boat Building Regulations | Flotation http://newboatbuilders.com/pages/flot.html
    A boat builder or manufacturer can use what ever means they wish to achieve the required results. Foam is not even required. However if foam is used, AND it will be exposed to gasoline, oils, bilge cleaners and other solvents then it must meet the standard quoted above. However if it will not be exposed to those things you can use whatever foam you wish. There are ways to achieve this. If polystyrene is used and it is encased in fiberglass, or bagged in plastic, or in a sealed compartment where gas or other solvent cannot enter then it works just fine. I have used polystyrene flotation on my own boats. It is bagged and sealed. Or if it is not in the bilges and away from places where it would be exposed, it is fine.

    Second: There is no such thing as US Coast Guard Approved Flotation Foam. If a foam manufacturer tells you this then they are hopelessly misinformed or blowing smoke. The Coast Guard does not approve flotation foams. It is the boat manufacturers responsibility to certify that whatever they use meets whatever regulation applies to it. You will find foams that say Coast Guard approved and have an approval number. Those are not flotation foams. They are fire resistant insulation foams used on commercial passenger carrying vessels, in bulkheads and walls, overheads and elsewhere for insulation. They are very expensive and do not make good flotation.

    Third : There is polystyrene foam and there is STYROFOAM (which is a polystryene foam) STYROFOAM is a trademarked name and easily recognized because it almost always white and has a large cellular structure, It is also very friable, meaning it comes apart in little pieces. We have all seen this in packaging, floating in the water, and blowing in the wind. Then there is polystyrene insulation foams used primarily in construction of buildings and houses. It is not stryofoam. It is much denser and has a much smaller cellular structure. And yes it is cheaper. But it makes excellent flotation foam because it does not suffer from the water absorption problems that two part blown, or pour foams. suffer from. However, if used it must be in areas that are not exposed to solvents, or encased or bag so that these liquids cannot contact it. These are all true closed cell foams

    There are also Polyethylene foams. They are primarily used in water toys and pool noodles and are sometimes used as packaging for fragile items. It is more expensive than polystyrenes and polyurethanes, but does make good flotation foam. , additionally it is not affected by gasoline, oils or petroleum products. Some boat manufacturers have used polyethylene foams for flotation.

    Then there are the mixed foams, usually two parts, poured or blown into compartments, that then expands. These are polyurethane foams. These actually make good flotation foams IF done properly according to the foam manufacturers instructions, Simply mixing it in a bucket and pouring it in is not sufficient. The foaming process is very sensitive to humidity and temperature. They are also sensitive to exotherm, the heat generated by the foam itself when expanding (due to a chemical reaction). If too hot the cells are too thin and begin to break. If not enough heat the cells don't form and you get something that looks a lot like bread dough. If the foaming process is not done properly with clean equipment, then the foam will absorb water. This stuff is notorious for that. But if done correctly it will last for many years with no problems. The Coast Guard has tested literally hundreds of boats that use this. A small percentage had issues with water soaked foam.

    I can show you examples of all kinds of flotation materials that all passed the US Coast Guard flotation test. Even plastic bottles and soda cans.
     
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  4. rwatson
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    rwatson Senior Member

    Hi Rodney
    Good to talk to you again about foam flotation in Australia. Though you only mention small vessels, I wasn't sure if you wanted them up to Commercial Standards

    For Australia, this might be a useful reference
    https://www.amsa.gov.au/file/805/download?token=092aPdPn

    Not only does it reference the particular standard of foam

    "BRITISH STANDARDS BS 5241-2: Rigid polyurethane (PUR) and polyisocyanurate (PIR) foam when dispensed or sprayed on a construction site. Specification for dispensed foam for thermal insulation or buoyancy applications."

    But it also provides a template for describing the types of spaces under different loading conditions.

    I hope it's of some use.

    Floodedspaces.png
     
  5. fallguy
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    fallguy Senior Member

    It must be noted that polystyrene is not for structural work of any kind, at least as a glass sandwich core.

    It has weak compression, although you can buy better qualities of it with higher compression.

    It also has poor shear. I did a peel test on a piece for fun. The peelply removal actually started the shear. I then held it down to stop the peelply from shearing more. But if you look at the picture; you will see the foam separated internally. While this is the goal of a laminate; the ease at which this occurs is the problem. This was not a technical test. I just wanted to know what might happen inside my livewell made with polystyrene. If the core shears, I might need another layer of glass.
    9835ABA4-F18C-4B4D-B6FF-CCF5E42E3A54.jpeg
     
  6. rwatson
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    rwatson Senior Member

    Strictly speaking, that's not Shear failure. That's delamination.
    I presume that was Epoxy you were using.
    You also have to be careful that the delamination wasn't caused by surface problems. I had glass/epoxy separate from high-density foam core, because of contamination.
    The clear edges around the glass indicate initial adhesion failure.
    Lots of surfboards use Extruded Polystyrene, without drastic failure like this.
     
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  7. tpenfield
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    tpenfield Senior Member

    I have a bunch of XPS foam, fiberglass cloth, and epoxy left over from my swim platform project. I'm thinking that I could run a test of epoxy/glass adhesion to XPS boards.

    I know that if you do not rough up the surface of the XPS boards, then delamination will be quite easy. I'm thinking that if the board surfaces are sanded prior to glassing them, then adhesion would be a whole lot better. As to how much better, perhaps I can run a pull test to see if the foam fractures before the glass separates, etc.
     
  8. Jolly Mon
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    Jolly Mon Junior Member

    Fallguy, I’m curious about how you prepped the XPS before glassing. I’ve got a companionway hatch and a aft cabin hatch that have been in use seven years and no signs of delamination. I can sit and stand on them.
     
  9. fallguy
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    fallguy Senior Member

    Strictly speaking; it is delamination on the edges and shear in the center. The clear areas delaminated from the peelply pulloff or due to edge compression under vac or Lord knows what.

    There was no contamination. This is not my first rodeo using polystyrene. I knew it'd fail. The only way I have been successful with polystyrene is to abrade the surface with 36 grit floor paper and hotcoat it with thixo. Basically this doubles the surface area (or so)...

    I was surprised by the edge delam and expected the whole sheet to bring core along.

    If you look real close at the core; you can see I started sanding it before I snapped this photo for all the xps hull ideas we hear. This never got relaminated; just glued down into the hull with foam glue.
     
  10. fallguy
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    fallguy Senior Member

    There was no prep. The best way to prep xps is to abrade with 36 grit and hotcoat it.

    But there are also varying densities of xps. The less dense stuff in my picture has a much lower shear rating than the higher density types.
     
  11. fallguy
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    fallguy Senior Member

    Most likely the core will still be the failure as desirable. The real question will be how easily. In my picture above it was sort of like tearing a sheet of paper.
     
  12. KeithO
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    KeithO Senior Member

    Extruded polystyrene has been used on many experimental aircraft, some weighing close to 1000lb and rated to +-9g acceleration so the wing structure is holding up +- 9000lb and the core is blue extruded polystyrene because the airfoil can be cut precisely using a hot wire bow.

    In this process, none of the original "skin" of the foam remains and it is quite possible that the skins are quite contaminated from release agent that might be on the tooling or from all the advertising crap that the makers print onto them.

    Not to say that this is the best core material ever, not at all, but it certainly is used to make parts that may be stressed a lot more than one might think.
     
  13. Jolly Mon
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    Jolly Mon Junior Member

    Keith that’s interesting. What skins are used over the XPS?
     
  14. KeithO
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    KeithO Senior Member



    This will give you an idea
     

  15. Jolly Mon
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    Jolly Mon Junior Member

    How did you remove the sandings?
    Vacuum?

    I used the green foam from Lowe’s. While I don’t see any delamination, i did have to repair the locking latch. It eroded over the years. I should’ve reinforced that spot from the beginning.
     
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