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Koda Vonnor

What about rigid molds?

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We have lots of great info here about making silicon and other flexible molds, but what about rigid molds? Does anybody have any tips or advice on those?

 

I have an armor project that is under way. I have taken plaster casts and am laying on the clay and shaping the armor plates. After I'm done with the clay, I'd like to make molds of the pieces. I'm having a hard time finding info about making rigid plaster molds from oil-clay models.

 

Does it need some kind of release agent?

If so, is there something that can be sprayed on that will not ruin the re-usability of the clay?

Is there something that can be washed off both the model and the mold?

Would soap-based agents be sprayable?

Would brushing on an agent leave brush marks in the mold?

 

I will be making layered fiberglass casts for all pieces, some of which will have slight undercut edges. All pieces will have non-cosmetic back surfaces, but none of these surfaces will be flat or level. Is this doable in a rigid mold or would a flexible mold work better?

 

Also, what are "mold walls?" I heard Thomas mention those in his project description, but have no idea what he meant.

 

Any help or advice on this step would be greatly appreciated.

 

~ Koda

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Guest bassclarinets

(i know someone who is rarely on the boards who may know more - i will poke them to get them to look on here) ;)

 

jen

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Pam could probably answer in more depth than I can after she gets back tomorrow, but... (the lekku molds start out as a sculpture in oil clay with an ultra-cal hard shell.)

 

You can make plaster molds over the top of the oil clay.

You'll want to coat the exposed plaster portions of your base with a heavy coat of vaseline to keep it from adhering together.

 

You will want to seal the clay with Krylon Crystal Clear spray. (to reuse the clay after this, you will have to scrape down the top layer)

 

Mold release.. with a rigid mold, you'll absolutely need one. To avoid brush strokes in your final project, use a very soft brush.

 

Mold walls and barriers you'll make out of clay to

1. make an exterior barrior for the mold. and

2. divide the mold into seperate parts. (if you don't make a multiple part mold with a rigid one, you're not going to be able to get your finished armor part out without shattering the mold)

 

What material do you plan on on making your final armor plates in? In many ways, that should determine what kind of mold you'll want to make...

THe benefits of a silicon mold for armor plate projects (where you're not looking for a cosmetic appearance back side) is that you won't have any seam lines anywhere. (of course, you'll still want to back the rubber mold with a rigid shell to maintain shape.) Additionally, you can successfully demold the original piece without damaging the clay. (Handy in case something happens and you end up needing a new mold) Downside: it's expensive, and does require a steeper learning curce than familiar plaster.

 

Benefits of a plaster mold. It's faster, and cheaper. But, you probably have a 90% or more chance of damaging the original sculpture while demolding.

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Thank you very much for the info, Scott.

 

I will be using polyester resin laminated with fiberglass cloth. I bought some gel-cote in black and white so I can mix up a silver/gray base color for the final pieces.

 

I guess I was most interested in how to prep the clay before I make the mold. So after the krylon crystal clear coating on the clay, and the vaseline coating on the exposed plaster, I'll still need a mold release on the clay, over top of the Krylon coat? Or were you talking about what to put in the mold before I start laying in the Gel-Cote?

 

I'm not too concerned with keeping the first plaster molds, as I will be making final molds of the hard-masters after I sand them all down smooth, but before I paint them. Those master molds will most likely be rubber, backed with plaster. I probably will finish and wear the hard masters though, rather than re-cast them in the master molds, since I'm lazy. :P I'll keep the final molds just in case. 8)

 

~ BC

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nah, once you've put down your crystal clear, you shouldn't need any additional release agent on the clay. (when it comes time to remove the molds from the sculpture though, get that sucker nice and warm, the clay will soften and make it easier to get your mold off.)

 

For making the final pieces in the plaster molds, I'd say you're definately going to need a release agent. Don't know that vaseline would be a good fit for that one though. Probably something thinner that doesn't capture brush strokes as badly.

 

Thank you very much for the info, Scott.

 

I will be using polyester resin laminated with fiberglass cloth. I bought some gel-cote in black and white so I can mix up a silver/gray base color for the final pieces.

 

I guess I was most interested in how to prep the clay before I make the mold. So after the krylon crystal clear coating on the clay, and the vaseline coating on the exposed plaster, I'll still need a mold release on the clay, over top of the Krylon coat? Or were you talking about what to put in the mold before I start laying in the Gel-Cote?

 

I'm not too concerned with keeping the first plaster molds, as I will be making final molds of the hard-masters after I sand them all down smooth, but before I paint them. Those master molds will most likely be rubber, backed with plaster. I probably will finish and wear the hard masters though, rather than re-cast them in the master molds, since I'm lazy. :P I'll keep the final molds just in case. 8)

 

~ BC

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What about sealing the plaster mold the same way as the clay? I thought I read something (in a wild gooling frenzy) about doing something like that. Then maybe some general spray release agent. I have seen them at Smooth-On and those type of websites. Any stuff you might recommend for plaster -> fiberglass release?

 

~ Koda

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