Epoxy over XPS method

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

  1. fallguy
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    fallguy Senior Member

    I assumed you were talking about using xps for a hull.

    The conversation is a little above my pay grade Eric.

    I used xps in my livewell. I glassed it all with 1708 and taped it with 1708; if it delams; not sure I care...

    I thought about using it for a table, but the darn stuff shears so easily; not sure it is worth the headache. Perhaps as a part of a stack with xps, san, glass...then the san would need to shear fully before trouble.
     
  2. Eric ruttan
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    Eric ruttan Senior Member

    I thought you built a table like groper. I guess not.
    May I ask, have you any idea what resin uptake of the XPS per square meter, as compared to PVC foam?
     
  3. Blueknarr
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    Blueknarr Senior Member

    I think the labor costs to arrange the trapezoid inter webbing would exceed the savings from using the cheaper foam.

    Would a 5 layer system (glass, 1/4 PVC, 1/2 XPS, 1/4 PVC glass) be more affordable?
     
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  4. Dejay
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    Dejay Senior Newbie

    Fallguy and Blueknarr, is there any info or thread about how to create lightweight insulated walls using such a stack? Preferably vacuum infused on a large table for saving work. Not sure how to search for that.

    It sounds relatively straightforward. Glass, something like 2-3mm structural foam with infusion channels then 60mm XPS insulation foam and the same on the other side. You could put thin strips of structural foam every 1.2m between the xps sheets too.

    But I haven't seen any discussion about the need for insulated on lightweight boats. Adding insulation to an already structural wall is easy but it wastes the stiffness that can be gained by XPS over a bigger area and neglects the extra work doing this separately.
     
  5. fallguy
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    fallguy Senior Member

    probably the way to fly, but if you were going for anything less thick; it is out; it is still a lot to laminate such a stack for a full hull panel; imagine 100 square feet of that and mixing thixos; you probably can't do both sides in under 60 minutes (both sides meaning both pvcs)..

    the other issue is the xps likes to crush even with 10" of Mercury vac on the edges; so you'd probably need pvc placeholders (perhaps not)...I just know the bag crushed the edges of it when I laminated it to san (no san on top), but if you bagged one side at a time; you need san or pvc edges for sure

    but I really like this idea for an ultralight tabletop or others; I recently built a rooftop and needed an elliptical shape and such a stack could be moulded even and you get some hold from the thixo bonding medium

    I need a 42" wide rooftop and want a wee bit if curve to it and figured I had to put beams in it, but this idea is really attractive; perhaps with two layers of the 1/2" pink or three even for a hardtop where hot sun would beat down on the operator

    I don't mean to burst any bubbles here. I just think once you get really complex; you have lost. Now, don't get me wrong; industrial processes can be complex. They/we corrugate plastic like cardboard. They/we could surely corrugate xps, but at what cost..and what ultimate quality

    corrugated plastic, for example is tougher than profile board, but can't be used for signage well because it isn't flat even...

    the other thing about stacking it...san core in thicknesses is fairly unaffordable and not often practical to ship a single sheet..for my tabletop; if I stack xps, I could placehold the edges with san scraps and my edges are easily formable and I can also put glass onto the top of the stack under vac; then flip it and vac the other side..xps does not form as nice

    in the past, whenever I used the xps, I abraded it with 36 grit floorpaper and hotcoated it..this is to help it with shear problems...

    if you were still nervous about sheer; Ruttan's idea or something like it would be wise...you could placehold some pvc or san in the betweens on edge to avoid delam

    thank you all for contributing; I may try the trapped xps idea for my hardtop...it also needs hardpoints, so the thing is a bit complicated

    as for my table, I have not done it yet.. The cabin exterior needs to be finished so I can shuck it outside and get some shopspace back. The other hull is also ready to fair..
    370D23F2-92C3-4583-8A61-F3F5020ABC1B.jpeg
     
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  6. fallguy
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    fallguy Senior Member

    I finger sketched the hardtop..No curve and no hardpoints.

    12mm san and two layers of 1/2" xps with the sheer web idea in just san

    this could work for my hardtop and no head dinging beams underneath

    thank you guys for working this idea..I had given up and perhaps got a gift; now it is true that I can build this all with san, but truth be told; I am getting toward the end of supplies and a sheet of xps is easily available for 20 bix local HD

    This is a removable top; so ultralight is best.

    finger-sketch-hardtop.jpg
     
  7. fallguy
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    fallguy Senior Member

    I did not answer you well here. It is far less. And this is why I abrade the surface with 36 grit paper and thixo hotcoat it. I can't recall if Dierking advised it; he may have..

    When I vac table laminated some 2"xps for my livewell with db1700, I shear tested it no abrading as I was told it was unneeded by someone here. It peeled off so easy. That picture is on the website here; perhaps this thread, but I will post it again. Look closely at the xps..I did not abrade it like I did in the past building Dierking amas. And it held the laminate poorly. I scratched the xps with 36-40 grit lightly on a 45 so people could see the difference..

    This panel had more trouble. The edges did not seem to bond properly. See the white areas. I still don't know what caused that, but my guess is squeezeout or resin suckout from bridging related to the fitting location prepped in the panel (anytime I prep a hole in a panel it gets me).

    The lesson here is resin uptake of the xps is poor unless you abrade it.

    This is another reason the idea to hotcoat xps into a stack or just bury it between webs has some appeal.

    btw, I glued this down to my hull with foamular as is glass off; the top side of this foam has 12mm san; this panel was sanded on a timesaver sander with a profile so the livewell has a lowspot at the hole..
    5C8AA221-ED3B-40F4-82C8-4BA0653707B3.jpeg
     
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  8. fallguy
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    fallguy Senior Member

    D274A46B-6FDD-4A53-B074-9F5DA91BC184.jpeg Here is another livewell pic with more xps; if it delams; not sure I care; just want waterproof and insulated well enough to keep ice a few days fishing if we go for bigger stuff.

    The bottom is 12mm san on the 2" sanded xps.

    I glued xps to the san side exterior. We have a bunch of well fittings that can't handle 2" hull thicknesses and I can't risk delam on thru hulls..

    this still needs another coat of pigment even today as the top of the box had a bunch of tape seaming to do; the color here was a base coat only
     
  9. Eelco
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    Eelco Junior Member

    Simplicity of construction. Just stacking foam blocks between 2d laser cut templates, trimming the foam in place with a hot wire, and building up your boat that way, seems like a fairly straightforward work flow to attain any complex hull shape. The only precision work requires would be to cut the templates and you can get that done professionally for peanuts compared to the cost of a boat.

    Getting the truss structure you envision in there seems like it would work for creating flat wall structures; but how to pull that off in a practical manner to execute some compound curve shape, is not obvious to me.

    Perhaps building up the hull in longtudinal sections could also be done using a vacuum bag approach? Not sure these are mutually exclusive. Thinking more about it, you could also cnc cut your triangular extrusions, and angle them to build up sections of your compound curve, weave the glass between them dry, and then vacuum infuse one section at a time. You could only need to precisely cut the mating surfaces of the triangular foam blocks so they fit together to form the intended curve, and you could shape the exterior surfaces with a hot wire in place as per above.

    Not entirely sure about the practicalities of that; but as others have noted its good to stay focussed on those practicalities; because good foam may not be cheap but neither is labor.
     
  10. Eelco
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    Eelco Junior Member

    Or how about this: fit blocks of foam between your 2d templates. Tack the blocks to the templates with some drops of CA glue, but properly glue the faces of the foam blocks together. Then hot wire the internal and external contours into them. Break the foam ring built up free from the templates, and then just freehand-chop this foam ring into mutually fitting angled triangular/trapezoid pieces with your hot wire. Put back together again with glass woven in between, tape a vacuum bag around it, and there you go. After this is all done, put some external skin layers on to tie it all together.
     
  11. Eric ruttan
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    Eric ruttan Senior Member

    More affordable than just PVC, sure. But you cannot infuse a foam stack. you have to laminate the foam then infuse.
    I think, as I detailed, light glass strips holding the sticks parallel and spaced would greatly decrease the labor compared to loose sticks.

    I think clean breeze was 66' and made in a cedar strip like process. that's a lot of work.
    Mostly boat builders want to build a boat, not buy a boat. Perhaps their labor calculations are different.
    there are a few vendors that claim to have laminated foam. This COULD save weight, and perhaps cost as well, as the core requirements decay to nothing at the center of the core and go back up to whatever you speced on the far side. And, if I understand the physics right, this is a straight linear change.
    So, if you imagine a foam core as having two halfs, a top and a bottom. And each half needs the compressive strength of whatever the spec is on the top, and zero on the bottom.
    Then any foam thickness requirement decays by whatever portion of this half thickness. As an example, the full core 1/4 PVC, 1/2XPS, 1/4 PVC foam suggestion by Blueknarr.
    That is a 1/2 PVC and 1/2 XPS for the imaginary top and bottom core halves. If the PVC needs be 100psi compressive strength, then the XPS would need 50 psi.
    If you redid the above with thirds, the top third still needs 100psi, the middle third needs 66psi, and the bottom/center third needs 33psi. This would be a stack of 5 sheets. 2@ 100psi sheets that are 1/6 the height, 2@ 66psi sheets that are 1/6th the height, and a middle third of 33psi. but also the resin adds something there
    And that is all true if I have not screwed up, and I can almost guarantee I have.

    Also note each foam change costs 200gsm resin PER SIDE, 400gsm to laminate two PVC sheets, and the cost (labor?) of laminating. Resin is not cheap.
    here is a thread where groper builds a table, and fallguy asks about it.
    Epoxy over XPS method https://www.boatdesign.net/threads/epoxy-over-xps-method.61414/
    groper cheats, or optimizes, here by having a low requirement domain (table, not hull), with a super tough outer shell (ply), super cheap core (xps), and makes it look like solid teak (artistic trickery). He is cheating all over. And it looks and works great.

    But, I suggest fiberglass cloth is the cheapest strongest thing, and its structural qualities beat any foam all to hell. Corrugation as a technology is well understood. Perhaps not in the foam fiberglass domain, but still.
    So cheap foam and a decent corrugation technique should beat any foam core, once you assume a certain core thickness.
    Agreed.
    I am hoping to keep the strips adhered to a thin retainer to keep them square and spaced. Then this becomes a bottom 'sheet', a corrugated layer that is a structural infusion path, and a top 'sheet'.
    So, perhaps, not that complicated.
    And this idea only really works with something like the C50 – HARRYPROA http://harryproa.com/?p=1749 that Dejay originally linked too. @Dejay your link in this post is broken Epoxy over XPS method https://www.boatdesign.net/threads/epoxy-over-xps-method.61414/page-4#post-849897 Can you inline the image you desired. I think a lot of people are missing this. i'll put a simular pic here too.
    http://harryproa.com/wp-content/uploads/2018/10/Or80-Explorer-001.jpg
    bah, cannot use gallery.
    Can you detail what you mean by placehold and why it is difficult to vac XPS? and the problem with the edges? Were these problems with 25psi XPS? these problems would be expected with 15psi XPS, but unexpected with 25.
    I should also not you do not have sharp edges in Rob's designs. the foam edges all taper.
    Can you detail an estimate of how much less? I am looking for someone with hands on vac laminating this small cell 25psi to compare observations with. Rutan airplanes use XPS, but it is a very course cell foam, much like PVC.
    for the reader, the foam fiber interface is always an issue. even in PVC foams they groove the foam with 2mm X 2mm grooves, that fill with resin, to get better attachment for this interface.
    This is another reason why XPS seems perfect for corrugating glass. We do not care about the foam glass interface, as it is only for manufacturing, not in any way structural. the structural part is the glass web to glass face interface, which is as good as one can get.
    Very interesting. Although I imagine not an issue with infusion, perhaps, as such an area should be flooded.
    yes. which is ideal for corrugation. less resin, less weight, less cost.
    Thank you fallguy. Thank you very much.
    How do you cut in place with a hot wire? I am not understanding what your suggesting.
    as noted above, this was in regard to the Rob Denney design that Dejay linked to. his designs are slab sided squareish surfaces. But, to address your point, if the curve was 2d, i think you could put the trapezoids across such a curve, which makes the curve a series of flats. Rob's designs do not have structural bows. they are crush zones, so you can do something different/traditional there.
    Robs building technology is rather flexible, but in general, you infuse a half hull at a time. if you are space constrained I believe you could infuse 1/4 hull at a time. I cannot see why you would infuse smaller portions. One could vary the interface angles and make a segmented curve. in theory you could also have a light compound curve too, if you can get the sticks and glass to stay in place till you can pull a vac on it.
    I am not sure one can reasonably argue DIY boat builders value labor.
    as I am having difficulty understanding this, I cannot contemplate. I appreciate your patience here. I do want to understand what you are saying.
     
  12. fallguy
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    fallguy Senior Member

    CA glue is unfriendly with foams..I think the SAN smokes if you hit it with ca. not sure about xps

    placehold...I mean a shear web, basically or in my drawing, the vertical blocks so the vac won't crush the xps foam when you glue up the stack and this would allow you to wetbag one side glass AND use the vac for mould pressure..

    a very light vac crushes xps...pretty sure I was using 250 foamular... 10" hg gauge is the lowest my system will go and it crushes

    bleedout was a problem as I mentioned wet bagging because the xps does not suck much resin

    I am stsrting to wonder about building my countertops and tables with teak plywood bonded to xps...sure would be pretty..
     
  13. Eelco
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    Eelco Junior Member

    Here is a vid about cutting 3d foam shapes use 2d templates. Idea would be the same as for this wing; except the templates would be entire sections of your hull, rather than sections of a wing.


    Once you have a foam section of your hull cut in this manner (could be a full annular section if the deck is moulded as part of the same process) between two templates, you can proceed to chop up that monolithic piece into triangular chunks, and the precision of the cuts matter next to nothing at this point; the important part is that it fits together nicely again, which it will, so ideally youd match the thickness of your cut to the thickness of the glass you are putting inbetween.

    I suppose you could do that for the whole boat and infuse the thing in one go; but it strikes me as more practical to build it up one section at a time, so you can work relative to the previous piece thats already nice and stiff, rather than an ever growing contraption of foam blocks which are barely holding together. But if the boat is small enough doing it in one go might be preferable.
     
  14. Eric ruttan
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    Eric ruttan Senior Member

    why glue comment?
    Ah, I am imagining just infusing both sides and the core in one go.
    If your foam was crushing, at just 10", i can see why you did one side. That had to be 15psi, right?
    I find i can vac 25 just fine and no crush. which make sense as it is almost twice as strong as it needs to be.
    I pulled <1000 microns on FOAMULAR250 (could not hold it), and had minimal movement. Which is as I expected.
    this makes sense now.
    but, can you guess how much resin to wet out the XPS, compared to PVC foams? if PVC is 200gsm, is XPF a half, quarter, tenth?
    You have a guy who did it for help. You got the skills. Why not?
     
    Last edited: May 24, 2020

  15. Eric ruttan
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    Eric ruttan Senior Member

    Interesting.
    But how to infuse those chunks? Or are you thinking wet layup?
    Well, one half hull, or whatever large piece makes sense.
     
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