Should I be concerned about slow cure with Vinyl ester resin under Divinicell?

Discussion in 'Fiberglass and Composite Boat Building' started by fly186, Dec 16, 2016.

  1. fly186
    Joined: Nov 2016
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    fly186 Junior Member

    I'm building a hard top for a center console that will be attached to the T-Top frame and basically replacing the old fabric top. I will use 1/2" H80 Divinicell as the core material. I'm planning to use vinylester resin and the lamination from top to bottom looks like this:

    - 10 oz E Glass
    - 1708 Biaxial cloth +/- 45 degrees
    - 1/2" H80 Divinicell (5 lb/cu ft)
    - 10 oz E glass

    The top is slightly curved and looks something like this:
    T-TopView.JPG

    I know I'll need to do some fairing on top and bottom and will finish with a high-build primer and Alexseal, etc.

    I'm going to build this from the bottom surface up using a male mold. I am planning to vacuum bag this in two phases (at least a few days apart):

    Phase 1: 10 oz E Glass and the 1/2 DCell core
    Phase 2: 1708 and 10 oz on top

    I'm concerned that in phase 1 I will be trapping styrene underneath the core and may get bubbles plus have curing issues if the styrene vapors cannot escape from under the core material and the vacuum bag.

    I'm going to laminate a 1'x3' test panel this weekend to check weight, strength, cure time, and to practice vacuum bagging, etc. but wanted to get opinions on this before I proceed.

    Thanks in advance.
     
  2. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Yes, slow cure with trapped styrene can dissolve the foam if it sits there long enough.

    If you perf the foam, or allow it to breath, then it won't trap the styrene, but you still want the VE to cure in a reasonable amount of time.
     
  3. groper
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    groper Senior Member

    I've done this before and yes you can trap air under the foam and you won't know it's there until you demold it. To prevent this you can use perforations in the foam to let the air escape through the core or channels in the foam so the air escapes toward the edges.

    I'd rather do this in a single step rather 2 steps. No cleaning up the surface after step 1 and less work in general. My advice is to first inhibit the resin by trial and error until you get a long enough gel time to complete the whole job without rushing. You can easily inhibit VE resin to give yourself a 4hour gel or longer if you need. Ask your resin supplier for a guideline of how much inhibitor to use and test some small pots first to make sure the dose is right. - you only need a few drops...

    Then bag the whole thing in 1 shot. Perforations in the core, peel ply over the laminate, perforated film over that to reduce resin scavenge , and then your breather over that and bag it.

    Practice on small pieces first if you haven't done this before...

    Also, put high density inserts where the supports are- these areas will see point loads and will crush the core if you have only foam there. You can use ply wood or PVC or ABS or thickened resin etc. Of you plan on bolting to the frame, just oversize hole saw the foam, backfill with thickened resin and re drill correct size hoke for bolts...
     
  4. terrnz
    Joined: Mar 2014
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    terrnz Junior Member

    ? why ?

    Did I read wrong?

    why on earth would you use vinyl ester above water?
     
  5. fly186
    Joined: Nov 2016
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    fly186 Junior Member

    Why vinyl ester? Well a couple of reasons but mostly cost and strength plus more working time. Another requirement for this top was that I wanted to attach a crows nest where one person could stand. No controls and it would be very lightweight and removable. As others mentioned, I do also plan to integrate hard points for attachments to the top as well as the outrigger bases and antennas.
    I'm starting to rethink vinyl ester and may go back to epoxy even if it is 2x the cost. I'm in SoFla so temps are not a concern. If I could get the epoxy to gel very slow and had at least an hour of pot life I would consider doing the laminations all in one go.
     
  6. ondarvr
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    ondarvr Senior Member

    You can typically get a much longer working time with epoxy, and with that laminate schedule epoxy is a much better choice.

    Stretching the working time out on VE can affect the physical properties, especially with a laminate that thin.
     
  7. gonzo
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    gonzo Senior Member

    If you are concerned about cost, polyester is the way to go. There is no real advantage with VE.
     
  8. fly186
    Joined: Nov 2016
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    fly186 Junior Member

    Cost of the resin is a factor but as I'm learning, it is not going to be that significant in terms of total cost of the project. What I don't want to do is spend all the time and money on this project and have problems.
    I was hoping that I could achieve the required strength and rigidity with one layer of 1708 and 10 oz cloth on the top of the core using VE. I've worked with West system epoxies and they always seem to retain some flexibility which I really didn't want here... or at least don't think I want.

    Since I don't have a lot of expertise in this area I'm looking for input from folks in this forum so if epoxy is my best bet then I'll go with epoxy. Not having to deal with the VE smell and vapors is also a big plus.
     
  9. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    All the slow cure epoxies ive played with will have more then enough time if the temp is around 70F,ditch the 1708, stick with just stitched glass,perforated core,peelply and keep vac under 50% youll end up with a nice surface that just needs a Little 220 before primer.
     
  10. fly186
    Joined: Nov 2016
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    fly186 Junior Member

    Thanks. I'm definitely leaning back towards epoxy and the perforated core but my local supplier says they have a hard time getting that. Not sure why but we'll see.
    As for ditching the 1708, can you explain the reasoning there if I'm looking for the best strength to weight ratio? I was hoping that the 10 oz on top of that 1708 will leave me with a "smooth enough" surface especially with the peel-ply on top.
    Remember, I'm going to stand on top of this laminate.

    Thanks again.
     
  11. Tungsten
    Joined: Nov 2011
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    Tungsten Senior Member

    Thicker core for stiffness and from what ive learned around here more glass on the bottom side for additional stiffness.

    if weight is a concern and epoxy is used then matt really has no use.
    5/8 core say 18 oz stiched each side will be pretty light and stiff.It will dent easy though but that shouldnt be a problem.Could even add the 10 oz on the both sides side to stiffen even more.
    Ive always just drilled holes myself in the core
     

  12. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Drilling the core is easy on a small job like this, it gets old quick, but it's not hard.

    Skins should be the same on both sides of the core, but if one side needs to be a bit more durable it can be lopsided. CSM just sucks up resin quickly and doesn’t add much to the strength, and isn’t needed with epoxy, so add a layer of stitched or woven glass to increase the thickness if needed.
     
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