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Nicodemus

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Plastic and Foam Experiments [Sep. 19th, 2004|02:15 pm]
Nicodemus
I've been experimenting with some two-part plastics recently. My goal is to be able to create a relatively hard and smooth surface on carved foam props. Here's the results.


The candidates are both commercial plastic resins that can be mixed and poured easily. They have similar chemical compositions, I suspect, though they dry slightly differently.

QuikCast, available from TAP, dries white (about the same opacity as milk). Smooth-On, from Douglas and Sturgess, dries mostly clear. For my application the color isn't a big problem since the plastic will have color added to it.

The plastics were tested on three different types of foams to see how they'd fare.



First up, common polyurethane open-celled upholstery foam. This would be convenient since it's cheap and easy to work with. But it has a very rough surface which makes it harder for the plastics to achieve a nice smooth texture.


Smooth-On (S) and QuikCast (Q) on polyurethane. The thinner areas are a single brushing of the plastic. The thicker spots are where I gave it a couple passes as the resin was beginning to gel.


This low-profile shot shows that the rough texture of the foam affects the plastic's surface. Not what I'm looking for.


Second, I tested the plastics with Ethafoam. This is a closed-cell ethane foam. Also cheap, but not quite as nice to work with.


Both plastics, Smooth-On (S) and QuikCast (Q), skinned pretty well. They could be spread shortly after mixing, leave a good surface, and not show brush strokes. The problem was...


The plastics didn't stick to the foam. They couldn't bond with the foam at all, really. As soon as the foam was flexed, the plastic sheet peeled away effortlessly. So Ethafoam isn't at all useful with plastic resins.


So we move on to crosslink foam. This is a denser crosslinked polyurethane (and other polymers) foam.


This is the best case for the plastics. They form a good surface and adhere tightly to the foam. The only downside is that this foam is about four times as pricey as the regular open-cell stuff. But, hey, it works well.


So there ya go. Hope this is of interest to any fursuiters interesting in building plastic things.
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Comments:
[User Picture]From: aeto
2004-09-19 10:16 pm (UTC)
You may also want to consider epoxy resins as well as poly ones. There are some cool additives for them which make them more vicsous. This may make them work better on the foam.

(I've been doing epoxy and silicon casting all weekend, myself...)
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[User Picture]From: nicodemusrat
2004-09-19 10:37 pm (UTC)
I was worried about the epoxies being too brittle for my purposes. I'm going to be creating some armor pieces that will be exposed to some flexing. I was hoping that these plastics might be more resistant to cracking. (Don't know.)

Any specific epoxy recommendations?

Another possibility, which I didn't try yet, is to lay down some latex paint primer on the open-cell foam to create an initial surface. Then the texture might not be such an issue.

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[User Picture]From: aeto
2004-09-19 11:04 pm (UTC)
It can be brittle, true. That's what the fiberglass is usually for, under the epoxy. I would be just as worried about the poly resins as well; I don't know how well they stand up to flexing, so would definately want to test that.

I like the West System epoxies, though they are a bit on the pricey side. Tap has a marine-grade epoxy kit which is nearly as good as the West System stuff, at a much lower price. Microlight is your friend, but not if you want the end product to be strong. Consider adding some collodial silica to give it some extra flex if you don't want to use glass under it. It also greatly adds to the adhesive quality of the epoxy.

For the masks I am making now, I use an outer layer of epoxy with a mix of silica and Microlight to give it the smooth, faired surface, then a VERY THIN layer of glass under it, to cut out the brittle nature. Add the glass around 1 hour after setting in the thickened mix, so it's starting to gel, but still fluid. Press the glass in, then paint that with epoxy with a small amount of silica mixed in. This seems to work well; you can do a full cast in around 1 day this way, working an hour or so, breaking a few for something to cure, working, etc...

The end result, if you do things right, is wonderfully light for its strength. If you are REALLY serious about strength and light weight, use layers of carbon fiber rather than fiberglass. I've not personally used it, but it has a very nice strength to weight ratio. It's not cheap, though...
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[User Picture]From: foofers
2004-09-20 02:42 am (UTC)
Say, have you seen Dia's rat's axe in person? That was atomized metal powder in liquid latex. Though not super gleamingly bright, it still parses reasonably well as metal, and of course is quite flexy.
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[User Picture]From: diadexxus
2004-09-19 10:57 pm (UTC)
BTW, Terraluna has a lot of experience with QuikCast... :) its neat stuff... if you have any questions about that particular plastic, he might be able to help ya.

It's also what Vortex's claws are made from. :) seems extremely durable.

-J
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[User Picture]From: nicodemusrat
2004-09-19 11:00 pm (UTC)
Oh, I've used the stuff many times, myself. Good material. I've just never tried using it as a skinning agent, only as a casting compound.
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[User Picture]From: ysengrin
2004-09-20 05:59 am (UTC)
... common polyurethane open-celled upholstery foam. This would be convenient since it's cheap and easy to work with. But it has a very rough surface which makes it harder for the plastics to achieve a nice smooth texture.

We've used this with the smooth-on smooth cast 300 (rather than the 325) - it sets 'hard' faster, while the 325 stays rubbery longer. We saturate the foam and let it set - then sand as needed. If you needed a shiny / smooth surface I assume you could polish it after sanding, but we haven't tried that.

The 300 also sets white, as opposed to the 325 clear-ish set. We also use it to 'set' plaster bandage forms into a much more rigid and durable working surface.
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