I have made my scale sheet. It sits in my yard, covered in dry plaster. I tried to lift it carefully and it cracked very quickly.
It's a clean crack and I'm confident I can patch it without comprising the cast. But I AM prepared to have to re-do this....
How can I safely move and flip this massive cast without destroying it? AND/OR if it does get destroyed, how can I avoid this in round 2?
Thank you!
Plaster is not a good medium to cast large objects in unfortunately, as it cracks when you move it far too easily. You may be able to turn it over successfully if you support it very well (you may need additional people to help), but it will be difficult. You can use burlap strips to help reinforce the mould, but if it is a full size one, I'm not sure how much that would help. Also, you cannot get many casts from a plaster mould, they start to degrade very quickly. If you can salvage this one, coat it in an acrylic gloss (test that it is compatible with silicone first) to try to protect the surface. Otherwise if you can't, I would recommend a different moulding material, there are lots out there that are suitable! Good luck!
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Ditto to Kate~
Honestly, I would cut your losses with plaster. You'll spend more time with a headache trying to get that mold to work, than spending time to redo the whole thing.
Forget plaster, Go with Resin based (Shellshock) or fiberglass resin (Bondo/ ect) They will be sturdy and will hold up to multiple pours and handling.
Sorry <3
I'm actually gonna go one further and recommend a flexible mold material rather than a rigid one. Even though hard plastics and resins work well and are much sturdier than plaster, I have heard they are still prone to cracking and can have very sharp edges that can cut fingers if you're not careful. Plus you have to spend ages cleaning the clay (or foam scales or whatever material you've used) out of the mold afterwards. Everything about it sounds like a headache, honestly. I use urethane rubber for my molds, and not only is it easy to use, it's insanely easy to demold (I use Vaseline to make things easier even though you don't even need a mold release with clay, but I can literally just peel my molds straight off my sculpts and the sculpts stay in such perfect condition I can make multiple mold copies from the same sculpt) and the molds are so durable I can throw them on the floor or against the wall and it doesn't hurt them. I honestly don't know why more people don't use flexible mold materials. It's not cheap but in my opinion it's completely worth it for its ease of use and durability.
I'm going to ask the silly question, just for peace of mind Theobromine; is urethane is compatible with platinum silicone? I heard that they won't bond, but it's fine to use for moulds, or is it only particular kinds that are safe?
I think one of the reasons urethane is less popular (at least in Aus) is that it's harder to get (and I assume more expensive) than fibreglass, but it does sound excellent!
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^theyre safe! And this is what I would use if I were to start over on my tail. Also I'm allergic to shell shock so
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Ooh good to know, I'll definitely consider it for future moulds! Also eek, that's no good
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Thank you everyone for so many helpful answers =)
I am trying to keep myself on a bit of a budget, though it's not too tight. Mostly I'm eager. Are these things I would have to order or could I find flexible or plastic casting materials at a local craft or hardware store?
No worries Miss Silverfin, it's perfectly safe and compatible, it's what I've used for every single one of my molds for every single thing I've ever made from silicone and it works so well I've never even bothered with anything else! So I haven't tested anything else personally, but I know there is urethane rubber and urethane resin, so just make sure you're getting the rubber kind (not 100% sure if the resin is compatible with silicone; I believe it might be but I haven't tried it so I don't want to tell you the wrong thing)
Mermaid Anahita, I totally get the craft budget thing. Craft stores only have a small range of mold materials and the only flexible one I've ever seen at one of my local ones is the amazing mold putty, which is a silicone putty but only comes in small boxes so it might not be cost-effective for a large project. I've never seen any flexible mold materials at a hardware store, just fiberglass resins pretty much. If you can find a more specific plastics or molding/casting type supply store near you, that would be the way to go. Do you have a TAP Plastics or a Reynolds Advanced Materials near you? Those are both great places to start (I get my urethane at TAP).
Also, you can actually use a silicone mold to cast silicone into, as long as you use mold release so the silicones don't adhere to each other. Silicone is very commonly used as a mold material in a lot of different industries! Some silicones are cheaper than others; none are as cheap as plaster but they'll all work far better. You just have to make sure NOT to use tin-cure silicone as it will inhibit platinum silicone! In fact...come to think of it, I might make a whole separate thread about flexible mold materials because even though I've referenced my urethane molds a few times in my own threads, I still see a lot of people asking questions about mold making an no one else seems to mention it! I don't wanna clog up your thread though
There IS a TAP near me, I had been there once to look at their platinum silicone (WOAH expensive) which is why it didn't really occur to me to go back.
If you don't mind me asking, how much do you buy it for, and how much do you need? I'm also thin so my scale sheet is rather small compared to some.
Yeah, their platinum silicone is super expensive. I calculated it out once and per ounce it's almost TWICE as much as Dragonskin @_@ so I just buy dragonskin. And the urethane is pretty flippin' expensive too, it's almost $200 for a 2-gallon unit (one gallon each of parts A and B). But you can get what is essentially a test/sample size for about $38 which was what I started with. It was enough to make me a lot of small critter molds that I used for my materials testing. Then I asked for the gallon-size for Christmas :P and I've gotten a crap ton of molds out of it (more creatures, two scale patches and several other random individual scale tests, my whole fluke mold and a bunch of different fin molds) and I still have a decent amount left (maybe 1/6 of what I started with?). I'd recommend at least going there and picking the brains of the employees. I've found them to be pretty knowledgeable, though it depends on who you get, but they at least have a lot more experience and knowledge of mold-making and such than anyone you'll find at a hardware store. Plus they supply all the odds and ends you'll need like mixing/measuring cups that are safe to use with the materials, mixing sticks, squeezy bottles and syringes...
You can also check out what Smooth-On offers. I haven't tried any of their urethane products yet, but I know they have a bunch, and they also have a bunch of different platinum silicones for mold-making. I've also been told about a company called Douglass and Sturgess that offers similar materials but I haven't done as much research on them.
I agree, go with a flexi mold for long term wear and tear. Good to know about urathane molds! I use moldstars, which is a platinum silicone mold for use with other platimium silicones...or anything really! I've just done a bit of an experiment with shell shock, but the jury is still out on that.
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Oh, one other thing I forgot to mention here is that you can also use the urethane (or silicone) to just do a thin skin coat on your sculpt, then pour a "mother mold" or support mold with plaster or other cheap rigid material. That way if the plaster breaks, all you have to do is pour a new mother mold but you won't have lost all the details of the sculpt. And the urethane rubber is durable enough that you really only need a very thin layer, and it captures details REALLY well (like annoyingly well, like it's picked up residual fingerprints on some of my sculpts that I thought I had smoothed out). So basically you can pick up the plaster outer shell (I'd still back it with fiberglass cloth to give it some strength, and that's pretty cheap at the hardware store). Then when you have that flipped over and set down where you want it, you can peel up the urethane skin coat and then just place it right back into the support shell (which is just there to keep it from distorting while you have the silicone in it). There are plenty of Youtube tutorials that will show you how to use these methods.
This is very helpful because I have the urethane on my scales, and it's been sitting for a while because some areas on the edges of the scales are thin and I was worried it would make little tears when I tried to remove the scale sheet.Originally Posted by Theobromine
Some urethane had also leaked through to the other side... I removed it as best as I could, and used the pieces with some fresh urethane to cover and patch some of the thinner spots.
So if I were to pour plaster over this prior to removing scales, would that help prevent this from happening?
Or am I worried to much, and the urethane is stranger than I think it is? Haha
Thank you all again so much for the helpful advise =)
The urethane is really strong. I wouldn't worry about tears as long as you've used enough mold release so it doesn't stick or anything. The plaster would really just be to support the mold and give it a level surface if the urethane itself isn't level (like if you just did a skin coat to save on urethane but didn't pour it deep enough so the back surface is flat, make sense?). Otherwise, I probably wouldn't worry about it! You can always just peel up a bit of the corner and feel it and see what you think. But I haven't had any issues with molds tearing, even really thin ones. For example, here's a small scale test mold I made recently, and you can probably tell how thin it is...the part you're looking at is actually the back of the mold, not the front.
Okay so I'm at a bit of a standstill and here's the situation:
I kept the plaster mold as a fail safe, it broke into large pieces and I can repair it if need be.
My scales are still sitting with urethane on them, most of the layer is thick and above the scales, with very few exceptions of some scales being close to the surface.
When pour g the urethane, some leaked through to the other side and I pulled it all off as best as I could.
I tried to lift a corner, but the urethane wants to break and split. The only thing I can think of doing is turning it over and picking out the scales and partially dismantling the scale sheet.
I have 2 gallons (1 gallon each part a and b) of silicone so I can really only do this once without getting more.
I'm not sure what exactly I should do. I'm very tempted to just repair the rigid mold and use that, but it would have made the urethane a complete waste.
Idk how to post photos here, but I can take some when I get home if that would help.
Any advise MUCH appreciated!
It wants to break and split? That's...weird. Mine definitely does not do that. Can you post a picture/link the EXACT type of urethane you used? Are you sure it's urethane rubber and not urethane resin or polyurethane or something? Did you mix it carefully according to the directions on the package? Pictures would definitely be helpful. You can post pictures by just clicking on the little icon of a photo (looks like a tree in a frame) at the top of the reply window. It's third from the right, after the talk bubble and film strip icons.
I will get pictures and brand name when I get home, but it is urethane rubber from TAP plastics, and it is still flexible. Also I mixed 50/50 as told by the instructions.
But I don't think I used enough release, and it's a little clingy along with some parts having creeped into cracks in the scales.
I'm worried about loosing too much of the edges, because my sheet is big enough to wrap around me with 1 seem, but I can double it and make 2 seams if I HAVE to....
Is it this stuff? http://www.tapplastics.com/product/m...king_system/63
Cuz that's what I use and I've never had that problem. Did you make sure to thoroughly stir Side B (the darker runnier one) before mixing both parts together? Side B separates, but if you read the instructions I'm sure you read that part too...if it's still flexible how is it threatening to break and split, exactly? I guess I'm just having a little trouble visualizing it. And what did you use as mold release? I use craft foam to build mold walls for my larger molds and I just slather on a bunch of Vaseline and the urethane lifts right off it. However, because it isn't very viscous it does like to seep into the tiniest cracks and grab hold. When that happens I've just pulled it out and trimmed off any extra bits. Maybe try peeling up just a small bit and testing how that feels?
It is that same stuff, I did mix up part B because I read it can sepparate, but I just shook the bottle. I mixed it in small bits at a time so I would only seeing this as being an issue in the very first batch (before there's enough space in the bottle to really shake it)
As for describing the issue I'm having, imagine an old rubber band. It's not THAT bad but when I tried to pull up a corner, it wasnt wanting to stay in one piece. It would lift with my fingers, then split right next to my hand where part was hanging on to a scale.
I have a few alright pictures of the whole thing, but it's possible the photo icon isn't displaying on the mobile version of the site, so I'll be able to get more specific when I get home.
I can even record a video and post it on YouTube for you to see
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