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Unread 01-13-2013, 10:59 AM   #1
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Monday Night Combat - Support Backpack

So I am making a Support cosplay from the game Super Monday Night Combat. I hope to have it ready for PAX East 2013 which is about two months away. I already have lots of parts and pieces made. The chest body armor, orange tunic, blue LEDs, and gloves are each at least 75%-90% done. The problem is that I've run into the hard part. Making his backpack. In reality it is not that big, it is just from his upper back up to the back of the head.

Thing is, I'm kind of struggling with what materials to use. I picked up a large block of Styrofoam that I'm going to sculpt into the right shape.


It is my understanding that to seal it, I need to use Gesso in layers, then sand, then paint. Can I use Spackle instead?
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I tried it out with Spackle on a smaller piece of foam, and while I like the way it looked, I found that pressing my nail into it would just penetrate through the paint and Spackle, exposing the white underneath it with no problem. Also, dropping it on the floor made a piece chip off. So it seems a little brittle.

Is there any way to coat the final product with some kind of clear stiffener? Or do I need to change the Spackle to Gesso? Or is that the problem with working with foam? That I just shouldn't bump into anything or handle?

I'm worried because I will be flying to PAX East, and I'll be putting the cosplay gear in a checked on box for my flight, and I know they sometimes handle those roughly. And i don't want the backpack to fall to pieces before I get to wear it. Not to mention bumping it into things/people at PAX.

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Unread 01-17-2013, 01:51 AM   #2
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Spackle I don't think would be a particularly durable way of getting this done, but I do have an alternative.

For my Shanks gun I wound up having to coat foam with bondo, then put fiberglass cloth + resin then more bondo. This gave a VERY strong outer coat, however it was labor intensive. I have since revised this method to just be masking tape, fibgerglass cloth + resin and bondo. The reason for the initial bondo/masking tape layer was to prevent the melting of the foam. I detail the build on my blog!


Good luck to you!!!

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Unread 01-17-2013, 02:52 AM   #3
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you may aslo want to switch to high dencity EPS insoltaoin foam
stronger and cheaper then your foam by the cubic foot
good times to all
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Unread 01-17-2013, 04:06 PM   #4
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Styrofoam + gesso alone is far too weak for anything beyond a quick throwaway prop.

For something slightly stronger, I'm a fan of Smooth-On's Shell Shock. No odor, fast cure, and it doesn't eat through the foam, so you can just brush it on directly. Ya gotta order it online though, and it isn't the cheapest product around.

For real strength, you've got to use some sort of composite; a combination of a fibrous material and a resinous material. On the weaker end you've got things like paper mache or muslin+white glue, on the stronger end you've got things like fiberglass + polyester or epoxy resin.

After you have that nice strong layer that holds your piece together, you need a layer above that which can be smoothed. The fibers in the composite layer make it too annoying to just sand smooth. You can sorta get away with it in paper mache, but even that tends to get all weird and fuzzy on you.

A lot of products work as this smoothing layer, jointing compound, wood putty, spackle, paper clay, epoxy, gel-coat, polyester autobody filler putty (Bondo), and repeated layers of white glue or gesso are all common choices.

My favorite choice for this step tends to be a mixture of Bondo and polyester resin. By mixing them, you have complete control over the thickness. Making it thinner lets it be applied smoother, and have fewer pinhole flaws. Making it thicker allows you to fill in large defects and prevents it from dripping or running. The higher concentration of solids also makes it quicker to sand.

You can do the same thing by mixing together resin (polyester or epoxy) with some sort of thickening agent, such as colloidal silica (aka Cabosil). Bondo, after all is pretty much just a mixture of polyester resin and talcum powder. The problem is that dosing out the right amount of powder is sorta difficult, mixing the powder evenly into resin requires either a lot of calories, or a power drill with a mixing attachment, and you gotta wear a good dust mask or risk getting silicosis.
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Unread 01-23-2013, 01:59 PM   #5
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Thanks for the advice. Going to be ditching the Spackle. I actually found this product which looked interesting:

Just add water.

Apparently it can hold up to kids jumping on it and is sandable.

I ordered one and I'm going to be testing it soon. If it turns out rough after sanding, I'll probably coat it in Modge Podge to smooth it out.

Took me like 12 hours to get the general shape of the backpack.

I just need to finish sculpting the back spine protector and a few more details and I'll be coating it in the foam coat.

While I'd love to go with fiberglass or resins or some fancier materials, my experience is lacking and my work area is rather limited unfortunately.
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