Epoxy over XPS method

Discussion in 'Boatbuilding' started by mvoltin, Nov 16, 2018.

  1. fallguy
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    fallguy Senior Member

    Here is a finger pull peel test of non abraded xps for you guys. The glass is/was 1700 or 1708. Vac bagged at about 10" Hg. Last 30 days to see if it needs abrading.

    Terribly easy pull apart. The way to improve here is wicked abrasion of the xps and a thixo coating prior to glass (primary bond). Of course, all this is doing is doubling the bond area and creating some bonding in another plane, etc.

    The xps has no shear strength and tears apart like paper. Look close, I started to sand it before I grabbed the camera for this thread.

    Marc's friend is lucky because xps is definitely not good stuff for much. Table tops. Or in my case a livewell insulator.

    955E9456-E7F8-45F1-ADED-72E108F45302.jpeg
     
    Last edited: Jan 2, 2019
  2. upchurchmr
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    upchurchmr Senior Member

    I'd be interested in "finger peel" of an abraded surface vs non abraided.
    I don't think they will be significantly different.
    But I'd like to hear about it.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Interesting that the OP never returned to the scene of the "crime" here.
     
  4. upchurchmr
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    upchurchmr Senior Member

    Maybe he got what he wanted, which probably was not our nitpicking level of information.
     
  5. fallguy
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    fallguy Senior Member

    Well, I will try a test piece near the end of the project. So far all the ones I heavily abraded are going into the boat. The one that peeled with no effort (none) was the base and I just glued it down no glass. It was a test and it failed.

    I ought to add, the peelply I used caused the initial edge delamination. I am using the red lined pp and it pulls pretty tough. I literally had to hold the glass down to remove the pp.
     
    Last edited: Jan 2, 2019
  6. groper
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    groper Senior Member

    my interest in using XPS lies with using it as an inner core, sandwiched between a higher density outer core, which is then sandwiched in glass. I would definately consider this application for large span panels which are quite thick to provide a very stiff panel - such as a bridgedeck floor in a catamaran or a large roof over the saloon in same. The reason for doing so is to reduce costs - nothing else. Building a 40-50mm thickness panel from PVC foam core gets very expensive very quickly. And for the large part - i think its probably overkill - especially on a roof. Floors have wave slamming loads to consider which would be the limiting factor IMHO.

    So basically im considering a 40-50mm thickness XPS core, with 6-8mm thickness PVC foam either side of that - perhaps even 4.5mm ply instead - followed by the infused quadraxial glass laminate of approx 1000gsm. The floor area would be quite large, perhaps 40 square meters or thereabouts and stiffeners provided at 1500mm centers. As you can see - a large panel like this done in PVC foam or other structural cores would be quite expensive. I think the XPS cored panel could do the job satisfactorily at a similar weight for much lower cost...
     
  7. groper
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    groper Senior Member

    What is the exact foam you are using?
    I would suspect that the foam you have has come out of a mold when it was manufactured and has mold release contaminates on the surface of it.
    Structural XPS used for structural insulated panels (SIPs) is cut into sheets from a block of foam so that the surface is clean virgin material and ready to be bonded. Im not sure about house insulation foam - this could be made in sheets on a mold surface and the surface of it could be contaminated with mold release agents or simply too smooth or shiney etc to be readily bonded...
     
  8. fallguy
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    fallguy Senior Member

    Owens Corning FOAMULAR 150 2 in. x 4 ft. x 8 ft. R-10 Scored Squared Edge Rigid Foam Board Insulation Sheathing-45W
     
  9. fallguy
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    fallguy Senior Member

    It is an interesting idea about release agents. Or some other factor. Not sure. I just know harder pull peelply will delam it in a 16 hour demould time.
     
  10. upchurchmr
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    upchurchmr Senior Member

    Groper,

    You still have a very flexible foam XPS in the middle of the sandwich which is exactly where the lack of shear stiffness will allow the sandwich to bend.
    A sandwich structure which bends is exactly what a sandwich is designed to avoid.

    Try a test sample, don't believe me.
    Make up two panels of equal weight and see how far each bends under a load.

    IMO, eliminating the PVC, adding the weight back in glass, will be just as good if you must use XPS, since most of the stiffness will come from the glass. It will be easier to build also.
    This will be similar to the homebuilt aircraft mentioned before - the one's I know of were Rutan's aircraft.
    In later more weight efficient designs, he would put the finished structure in an oven, baking out the XPS, and he would get a lighter structure.
     
  11. fallguy
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    fallguy Senior Member

    As a side notr, my neighbor has an unfinished Rutan (ez something?) sitting in his polebarn. He said family got in the way or he messed up a part of it.

    He said it can't be sold for liabilitt and he doesn't want or believe in hold harmless..

    Fancy dust collector eh?

    The stuff I linked seems to work fine if I hit it with floor paper

    Livewell guts. Corecell on the right for all the fittings for the well (expects thin wall) and corecell on the bottom for impacts. Xps on the side and ends with some balloon work. It also gets a cap of xps and gutters and lid. I will add xps pieces to the core side at the end for insulation.
    66BC9F2A-0BB7-4159-ABE2-E641685A0FEF.jpeg
     
  12. groper
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    groper Senior Member

    I don't think you're allowing for the thickness of the panel in your assumptions upchurch.

    By making the panel much thicker than a normal panel of the same intended structural design- you offset the core properties being inferior in modulus and shear strength by making the entire sandwich panel much thicker. If you assume equal panel dimensions and corw thickness- then yes i conpletely agree with you. But this is not what i want to assume here.

    So what im saying is that we design a panel which is at least twice the thickness of a PVC foam core but using xps in the center with higher mechaincal property materials around it to satisfy local design limitations such as compressive strength (required in a floor to prevent foot dents from people jumping on it for example).

    What you notice if you complete the required panel design equations is that much less is required from the core as the panel thickness increases. Extra glass on the skins is not required either as usually the strength of unidirectional glass fibers far exceeds that of the panel skin strain in bending loading. The increased flexibilty of the core increases the flexibilty of the panel all else being equal, but with 4x the inherant stiffness of a panel twice as thick- the resulting panel is still much stiffer than the PVC core at half thickness.

    So why do all this? Well to reiterate, its simply a cost saving measure. Large span panels on boats are very expensive when done in 100% pvc core...
     
  13. upchurchmr
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    upchurchmr Senior Member

    Make a test part and test it.

    Done.
     
  14. groper
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    groper Senior Member

    Theres no need!
    Many panels have already been made, tested, certified, etc etc...
    Structural insulated panels have been around for along time now- build everything from homes, commercial buildings, truck bodies, caravans, trailers, you name it... XPS is old news really, just the boating fraternity is a bit slow on the uptake by not realizing where it can be used and how- which is not obvious at first glance :)
     

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  15. fallguy
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    fallguy Senior Member

    You'll note their marketing people didn't even get the ability to mention marine in that sugary brochure. There were some debates; they lost. My hunch is the lawyers and engineers wouldn't allow it. I told a vp one day if he sold a product without a warning label people would die. He said, "you just sent me to jail".

    Despite my use of it in a livewell, I think it is a poor choice of material for a hull. And when corecell costs $5 a sqft and xps costs 0.5 a sqft, what always happens is some person comes on a boat builder website and says I am gonna build a 45' boat with xps and save 90% on core.

    I built my livewell base and sides with it and the vac pressure at under 12" Hg distorted the edges of the materials. Sure, the bag was tight there, but the point is the stuff behaves a lot differently.

    I think the distinction is about building a hull with it. I would not.
     
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