Hardening papercraft advice

Discussion in 'General Modeling' started by cayal, May 5, 2015.

  1. cayal

    cayal New Member

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    Almost finished my model and the inside is not accessible and not that well supported.

    I want to harden the outer so I can paint it, etc. but I believe if I use resin it will causing sagging in the paper.

    Are there any other options out there for me to use that won't run the risk (or lessen it).

    The project is the blades of chaos from God of War and it will be put on display rather than being used so it doesn't have to be insanely solid if there are options that can help there.

    I do plan on running a pva/water mixture over it to try to harden the paper before hand.

    Thanks.
     
  2. SkunkonToast

    SkunkonToast New Member

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    In the past I have used a polyurethane varnish sprayed very fine through my air brush working very carefully. Start with real light mist layers before letting that harden and then building it up slowly. never get the model wet as such, just build up very fine layers,, eventually it will gain rigidity and you can lay down a couple of slightly thicker coats. Always letting each previous coat fully cure first.
    Have a practice on something that doesn't matter going wrong and just remember slow and patient all the way.
     
  3. RogueTrooper

    RogueTrooper Well-Known Member

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    Resin is more than fine. 3 or more coats to harden it....then bondo (body filler/bog) it....then sand and sand and sand and sand some more...........;)

    A small amount of sagging is to be expected....bondo is the fix.

    No papercraft (pepakua) can be finished without adding a tough hard shell to sand and finish.
     
  4. rbeach84

    rbeach84 Sr Member

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    CA works too. But as noted - experiment first!

    R/ Robert
     
  5. cayal

    cayal New Member

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    What is CA?


    Thanks to all for the advice. :)
     
  6. rbeach84

    rbeach84 Sr Member

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    CA = Cyanoacrylate commonly known as 'super glue'. Use thin CA with paper (so it soaks into the fibers.) It sets almost instantly because of the fiber structure of the paper.

    R/ Robert
     
  7. RogueTrooper

    RogueTrooper Well-Known Member

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    I have to disagree;).......the dredd helmet I built was a pepakura base. No amount of super glue worked to adhere the card stock...all it did was make the paper wet with no bonding...Even the gel type of CA sucked big time....I used hot glue which worked well.....
     
  8. rbeach84

    rbeach84 Sr Member

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    Rogue, I was referring to "hardening" of the paper itself. I understood the question was about stiffening the paper which CA does by essentially 'soaked' into the fibers. I agree it is not good for gluing parts together - best glue for paper building is some kind of PVA (aka 'white glue') or other mechanical bonding yet resilient material. Your experience with CA for joining is common & mirrors my own - CA is fine when there is a matrix for it to 'set' into, but paper joints tend to be too flexible, of small contact area and suffer from shear stresses that CA cannot address, being strong in tension but weak in shear strength. PVA provides a mechanical bond while remaining a bit flexible.

    Regards, Robert
     
  9. RogueTrooper

    RogueTrooper Well-Known Member

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    Using superglue to harden paper is not a good idea. Superglue used in very small amounts to join very small (non paper) pieces together is viable. Using it to make large paper surfaces hard is asking for trouble.

    That's why superglue doesn't come in large quantities. It's not designed to be spread over large surface areas.

    Pepakura is building something using paper (card) stock. To harden the paper stock, fibreglass resin is ideal....slow drying and brushable.

    Superglue is dangerous at the best of times,
     
  10. rbeach84

    rbeach84 Sr Member

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    Please elaborate.
    UPDATE: Mulling over this, I considered some safety issues with rapidly setting CA which off-gases irritating ascetic acid & generates heat. However, if it is applied a bit at a time with adequate ventilation, there should be no worry. Also, as RT noted, the quantities typically available to the modeler are small enough to preclude creating a 'noxious cloud' or gluing oneself to a wall (for example.) Certainly, it must be handled carefully as always (no squirting it into your eye!) since it glues flesh so beautifully...

    The technique of stiffening paper & card stock with CA is essentially the same as using micro-balloons & CA as a filler. A micro-porous matrix provides the structural framework for the CA to catalyze quickly into a rigid mass. Applied to the paper in small quantities, a little at a time, it is quite safe. I'm sure it would be spectacular as a 'mad scientist' experiment if you could dunk a wad of paper in a bucket of CA - surely it would ignite from the heat generated!

    Polyester & epoxy resins have their own safety issues as do most all the materials we use in modeling, so it is just a matter of taking proper precautions and care & understanding the 'tools' one uses. If you want to be completely risk-free, you'd need to do something other than modeling - such as hiring a proxy to knit sweaters & doilies for you (the knitting needles have points...) In some circles, industry attempts to eliminate all risk from modeling has been blamed for the loss of the 'youngster' market (not to mention models that tend to fall apart all on their own.)

    Regards, Robert
     
    Last edited: May 14, 2015
  11. keithktam

    keithktam New Member

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    yea, i am building a papercraft with thick paper stock, and when i squeezed in the CA, I could see smoke coming out, i was a bit alarmed by that...
     
  12. blue2k

    blue2k Well-Known Member

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    Coating with epoxy resin will plasticise the cardstock. It is still flexible though, roughly akin to the compression you get from an empty soda bottle. It can "pop" back if it accidentally gets depressed.
     
  13. rbeach84

    rbeach84 Sr Member

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    The 'smoke' was the off gassing from the reaction, not the smoke of combustion... it is the acid that irritates the eyes.
    R. Robert
     

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