Has anybody tried using plaster of Paris?

[GenericCola]

I remember working with a CQB helmet project back during Halo 3, and after I pepped it and began hardening it with resin, I ran into a lot of issues getting into the smaller details of the helmet from the inside, and the resin isn't really cheap. Has anybody tried using plaster of paris to make their armor rigid?

Here are the ideas I'm tinkering with:

-Apply it to the exterior of the helmet for rigidity, then resin the inside without risk of warping.

-Apply it to the interior for rigidity, as it's easier to work with than the resin, then bondo the exterior.

Unless I did the resin incorrectly, which is possible, but I pretty much followed all the directions I found to a tee.

 

[Spartan1313]

I've never used plaster of paris for a helmet... but I have used it for other stuff. The only thing I would caution you about is that plaster is usually pretty brittle. That being said, if you do try, make sure to let us all know how it turns out.

 

[Carpathia]

This idea has been tried multiple times before, and about 90% of the time with less than stellar results.

When you initially resin your helmet, are you applying the resin on the outside, or inside?

 

[GenericCola]

This idea has been tried multiple times before, and about 90% of the time with less than stellar results.

When you initially resin your helmet, are you applying the resin on the outside, or inside?

I applied the resin to the outside-- it was when I tried to fiberglass the inside that I ran into problems.

 

[Carpathia]

One thing that you can try is what I do. After you resin the outside, slush a batch of thin-mixed rondo on the inside. That will fill in all the little crevices and give you a smoother surface on the inside, eliminating air bubbles when you apply fiberglass.

 

[wirewyrm]

There are several ways I've used to make it quite rigid without spending money on resin. You can check my starcraft thread for actual results images of my WIP, but here's my summary...

Plaster of paris. I've not used this, but it lacks any kind of flexibility in the final material, remaining fragile and brittle. I would avoid.

Cheap... papier mache. It's not impossible to use, but you should do very small bits at once and allow them to fully dry before continuing on. Resin dries fast and doesn't soak into and warp the pep like good old h2o does. Use a mix of around 75%-80% PVA glue to reduce the chance of too much water warping the pep. The paper fibre combined with fully dry PVA will be almost as rigid as the resin and glass, at least in my experience. It's fine to bondo onto.

Less good surface, but fast.... take all purpose filler powder and mix it with PVA till you have a gel. Paint it onto the inside liberally with a brush. It will take a while to dry, 24 hrs is ideal. It's not brilliant. I use this on the outside to bulk up some areas to save on bondo filler. The PVA will help to keep it together but it will eventually bend and it will be more brittle than paper mache or bondo. It may work to provide the rigidity to bondo or resin other parts if that's what you want.... you can also paper mache over it once it's dry with reduced chance of warping. As before, go careful and slow and things will go well.

The resin/fibreglass/bondo method seems to be the best for most people, but if you can't afford or use resin for whatever reason then give these a go.

 

[BiGHARYSCOTSMiN]

One thing that you can try is what I do. After you resin the outside, slush a batch of thin-mixed rondo on the inside. That will fill in all the little crevices and give you a smoother surface on the inside, eliminating air bubbles when you apply fiberglass.

I have a bad experience with that though... the rondo seeping out those little crevices and spilling everywhere...

So ever since I failed that with my magnum I've always resined then thin bondo then more stuff XD (as you can tell there was quite a lot of spillage)

Cheap... papier mache. It's not impossible to use, but you should do very small bits at once and allow them to fully dry before continuing on. Resin dries fast and doesn't soak into and warp the pep like good old h2o does. Use a mix of around 75%-80% PVA glue to reduce the chance of too much water warping the pep. The paper fibre combined with fully dry PVA will be almost as rigid as the resin and glass, at least in my experience. It's fine to bondo onto.

You know, that sounds like a great idea. I'd also remind whoever takes that word of advice that they wouldn't have to go very far to complete a piece of armor if it's going on the shelf or in a case. If all I wanted was a statue, I'd use that exact method to complete the helmet or whatever and paint. I think it'd keep it's shape.

Consider your applications for rondo/resin/elbow grease and size up your project with what you want out of it. Just throwing it out there- you don't want to go cheap if you want a durable suit!

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Now to get back on topic, no I don't think plaster is a great idea. Sure, people have used it, but Carpathivia and friends have other experiences with it as well. What I can tell you is, for smaller pieces like switches and covers plaster works wonders because it's easy to work with but when the scale of it's work field expands it struggles to keep up with strength in cohesion on a large surface.

In other words, plaster gets weak if it's too thin and used over a large space. I'd keep it interior and for small parts only.

There's still a world of unknown out there though, prove me wrong!

 

[Carpathia]

I have a bad experience with that though... the rondo seeping out those little crevices and spilling everywhere...

So ever since I failed that with my magnum I've always resined then thin bondo then more stuff XD (as you can tell there was quite a lot of spillage)

There shouldn't be any openings for the rondo to spill out. I'm talking a pepped helmet; if properly pepped and resined, there should be no holes for anything to seep out.

 

[BiGHARYSCOTSMiN]

There shouldn't be any openings for the rondo to spill out. I'm talking a pepped helmet; if properly pepped and resined, there should be no holes for anything to seep out.

OOOOHHH I thought you meant rondo-ing fresh paper...

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I found out long ago that resin binds to paper readily, fusing itself with the other unlike filler.

I also discovered that rondo doesn't bind with a layer of just resin as well as I'd like, so I tried attaching bondo to paper since resin is already in the material, and therefore the filler would attach more securely to the mixture.

The ONLY problem I had was the leakage of rondo. If I could master using rondo-paper... I would have a lot less explosions during sanding.

Speaking of which, lately I haven't used filler that often. When sanding, I really can't get myself to like filler on it's own and a lot of times in rondo. Like I said it doesn't attach onto things as strongly as I'd like a lot of times, so I've been mixing resin in powdered recycled paper and ash. Yep, ash. from barbecues.

I get ok results, but the powdered paper doesn't really help with rigidity so I end up getting expanded-resin... minus the strength. So more volume with less substance... equals not good. I'll experiment more but that stuff makes me happy to work with it. It readily binds to paper and doesn't strip or come loose and clog up the sanding procedure.

 

[RobotChicken]

I've used Plaster of Paris.....for patching walls, and making small Yoshi egg piñatas for a birthday party. I'd never use it on a costume, unless maybe for a China doll outfit. It's brittle, heavy, shrinks when drying, cracks easily, absorbs paint like foam (unless you seal it first), doesn't adhere well to other materials, and not waterproof. Resin is better for this application.