Quick question about the amount of silicone required to make a mold.

Hello RPF. This is my first attempt molding/casting so I'm having some trouble estimating how much materials the process will take.

I'm nearing completion on my first ever piece, a First Class Shaw/Magneto helmet. Here's a picture for reference:



It's about 13" x 8" x 9" if you were to measure it as a cube.

I still need to add the trim and finish the forehead crest (but I'm less worried about that since its going to be a different mold alltogether), but I plan on being done by this weekend so I can make my mold and start making casts. I went on amazon earlier in the week and bought this and this, as well as some mold release. I didn't really look at how much I was buying, but it came in the mail last night and I'm a little worried that I'm not going to have enough. I'm more worried about the amount of silicone since I can always get more plastic later, but I really don't want to get half way through the mold and find out that I don't have enough to finish (because I assume this will ruin the mold?).

Do you guys think that I'll have enough? One thing that crossed my mind was maybe using something else other than silicone to make the registration keys just to save on materials. I saw a video on youtube of a guy using thin slices of dowels, and I don't see why this wouldn't work. Does anyone have any thoughts on that. About how many helmets at a reasonable thickness do you think I can get from that amount of liquid plastic?

Also, did I get the right materials? I know there was several kinds of silicone available, but I didn't seem to find a definitive answer on which was best for helmets. If dragon skin isn't going to work, I can always buy something else and save this for another situation. Maybe the forehead crest?

My initial guess is that you don't have enough silicone to do the proper amount of layers needed for a nice sturdy mold. But I have been wrong before. Since you've already bought the materials, you can start your casting process, and if it turns out you don't have enough, just buy some more and clean the silicone you've put on already really well, and the additional layers should bond just fine. Dragon Skin will work, but I prefer Rebound 25 for mold making. Usually Dragon Skin is used for prosthetics. Are you planning on a two piece mold, or single?

I'm thinking a two piece, maybe side to side rather than front to back so I don't have to worry about smoothing things out on the widows peak part of the helmet. What's the best way to go about doing this? Making the mold in its entirety and cutting it, or walling off half and doing it in two parts?

Also, is it possible to maybe make the detail layer with the dragon skin, then smooth tube silicone on afterwards just to build up the thickness of the rubber? I saw a guy on youtube make his entire mold this way, but he seemed to have a lot of cleaning up to do on the final pull because of seams and air bubbles and such, but as long as that sloppy silicone work isn't touching the piece that shouldn't happen, right? I'm trying to think of local solutions so that I don't have to wait on something else to be shipped to me, and I can't seem to find pourable silicone mix anywhere in my city. How much does it matter about the thickness of the silicone if I plan on putting something like fiberglass or plastipaste on as a mold jacket?

Sorry for the barrage of questions, I'm just trying to make sure my first try at this goes as smoothly as possible and I don't end up wasting too much money.

Just by eyeballing it, I'd say you need at least one more trial size of your silicone to achieve a good mold thickness.

And even though you can always add more silicone later so long as it's free from dirt, dust, and release agents, it's always better to do it all at once to prevent that from even being an issue. And I definitely wouldn't mix and match types of rubbers. So it's either all dragonskin or all caulk.

As for thickness, it's about giving strength and shape to the mold to help it last longer. Molds go through abuse during the demolding process, just pulling the casting out can rip a thin mold. So it's better to beef it up. As a bonus, it will mate with the shell better and give you crisper details with less warping.

Have you thought about what you're going to use as a mold shell yet? You mentioned keys, but not the shell/jacket material, so I'm curious.

-Nick

I'm at the same stage you are with my first Model/mold and being that it's pay day, its time to make the order. The Smooth-on website has a little calculator that will help you determine how much you'll need to make a mold based off the aprox. model size and expected box size. It might help out some.


pitchforknumb On that matter of what to use, I was looking at the Moldstar 16 to make a 2 part mold of a prop gun, would Rebound 25 be a better choice?

Its between plastipaste or fiberglass, but I guess it really comes down to what I can go to the store and buy. I know I'll be able to get fiberglass, but I'm not sure about plastipaste. If I end up having to order more silicone I guess I might as well go ahead and buy the plastipaste as well, so there's that. Does the type of mold jacket effect the sort of keys I need to make?

ryanoh said:

Its between plastipaste or fiberglass, but I guess it really comes down to what I can go to the store and buy. I know I'll be able to get fiberglass, but I'm not sure about plastipaste. If I end up having to order more silicone I guess I might as well go ahead and buy the plastipaste as well, so there's that. Does the type of mold jacket effect the sort of keys I need to make?

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No, I just wanted to make sure you had the entire process sorted in your head. Sounds like you do, though. So that's good.

Also, I added a little more to my post while you were posting this, so check it out. I hope it helps.

-Nick

Ah yes, that makes sense. Did you see what I added in one of my earlier posts about spreading tube silicone onto the original layer of smooth-on for durability? In my head I don't know why this wouldn't work (assuming that all types of silicone will stick together), but I just want the opinion of someone who has done this before.

EDIT: Yes, you did see it, and you replied to it. Thanks.

Meadowhawk said:

I'
pitchforknumb On that matter of what to use, I was looking at the Moldstar 16 to make a 2 part mold of a prop gun, would Rebound 25 be a better choice?

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It depends on what kind of mold you're making. I like Rebound because it's pretty durable and will hold a verticle surface without dripping everywhere. But if you're going to be doing a box mold, and need to pour your silicone, go with the Moldstar.

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ryanoh said:

Ah yes, that makes sense. Did you see what I added in one of my earlier posts about spreading tube silicone onto the original layer of smooth-on for durability? In my head I don't know why this wouldn't work (assuming that all types of silicone will stick together), but I just want the opinion of someone who has done this before.

EDIT: Yes, you did see it, and you replied to it. Thanks.

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I've never tried this before, but I'm pretty sure tube silicone is not a platinum silicone since it air dries. It could work, but I think there would be a real chance of the tube silicone delaminating from the platinum silicone.

pitchforknumb said:

It depends on what kind of mold you're making. I like Rebound because it's pretty durable and will hold a verticle surface without dripping everywhere. But if you're going to be doing a box mold, and need to pour your silicone, go with the Moldstar.

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Thanks for the advice! Yea, I'm planning to do a box mold so sounds like I have the right one picked out. Is Rebound better for brush-on molds?

It looks like I'll be able to get a small size of some sort of smooth on brand rubber from my local Michaels, but it probably won't be dragon skin. Does this difference matter, or do you think it all need to be the same exact type?

Meadowhawk said:

Thanks for the advice! Yea, I'm planning to do a box mold so sounds like I have the right one picked out. Is Rebound better for brush-on molds?

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Yeah, rebound is pretty thick, and if you tried pouring it, you'd get a lot of air bubbles trapped. Make sure to post pictures of your gun. Sounds like a cool project.

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ryanoh said:

It looks like I'll be able to get a small size of some sort of smooth on brand rubber from my local Michaels, but it probably won't be dragon skin. Does this difference matter, or do you think it all need to be the same exact type?

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I'd stick with the same silicone for molding. Putting a different type of silicone, on top of another type of silicone could cause problems.

When did Michael's start carrying Smooth-On? Don't think I've ever seen it available at a hobby store...

pitchforknumb said:

Yeah, rebound is pretty thick, and if you tried pouring it, you'd get a lot of air bubbles trapped. Make sure to post pictures of your gun. Sounds like a cool project.

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Thanks I'll be sure to post a write up for anyone interested. I am doing the Colonial Revolver from BSG, it's been done before but I have some friends that would like one as well so I figured why not make my first piece something I'll reproduce.. no stress involved there! So far its coming along surprisingly well though.

I can't find it on their site, but I saw a very small box of it in the store a few days ago that said it had silicone, mold spray, and pourable plastic. I have no idea how much it costed, or how much was in the box, so I have no idea if its even worth it. I'll post tonight and let everyone know what I find out.

EDIT: So any advice on using something other than chunks of silicone for my registration keys?