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  #1  
Old 03-14-2010, 01:42 PM
Rob_Rob Rob_Rob is offline
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Smile Moulding & Resin Casting - really need some good advice

Hi, Iíve got a clay (normal grey clay) figurative sculpture which is 2 thirds life size and is quite complex for a novice such as myself to mould and cast in resin. Iíve never moulded and cast such a large piece before and really need some advice so I donít screw up the whole thing, I have quite a few questions and I understand reading this whole thread would be a little arduous so if anyone can answer just a couple of my questions that would be most excellent, and dare I say it a little bodacious too

The mould is going to need about 20 to 25 pieces. Whilst I decided to jump in and create something much more difficult than anything Iíve done before Iím getting slightly concerned Iíve bitten off more than I can chew. Iím really pleased with the sculpture itself but if things go bad then all my effort will be wasted which would dampen my spirits on this and any future pieces.

Iíve read up on an old forum thread (http://www.sculpture.net/community/a...hp/t-1915.html) about moulding and casting complex sculptures along with looking at a 3 part video on Ron Mueck entitled ďThe Most Realistic SculpturesĒ (on youtube). Part II of the video is very helpful to me in terms of the mould and Part III is a good reference for the casting process. The video links are here:
http://www.youtube.com/watch?v=pTy5c...eature=related
http://www.youtube.com/watch?v=Nh3SB...eature=related
What I understand is that Iíll need to create a bonded silicone, resin & fibre glass multi-piece mould. With a hollow cast made up of a release agent, gel coat layers and then laminated resin layers using fibre glass mat soaked with resin, 4 layers of laminate for a two thirds life size sounds about right going on the above thread. Whilst this is all really useful information a few points arenít mentioned in the thread or video which Iím unsure about, they are:

Mould
1. What thickness should I apply the silicone rubber and should it be cured or semi-cured prior to adding the resin and fibre glass?
2. Am I right in thinking the silicone mould will bond to the resin & fibre glass counter/mother mould? If not then does the silicone mould just sit inside the counter mould? if so that means I have to make the silicone mould quite thick to maintain stability inside the counter mould which is something I want to avoid to keep my costs down.
3. Does the resin and fibre glass need to be mixed together?
4. What type resin and what type of fibre glass do I need, and also what type of silicone do I need?
5. Will I need a wooden frame to secure the position of the mould as in Ron Mueckís example or is my sculpture small enough to get away without one?

Cast
1. Once the individual mould pieces have the gel coat and laminate applied how are they joined together? This really is a big mystery to me. Is further resin poured down the seams whilst rotating/rotacasting the complete mould? Or can individual limbs and parts on my sculpture made up of 2 or 3 mould sections be rotated separately which can then be attached to each other with resin and laminate?
2. There is a large hole in the mould at the back of Ron Mueckís pregnant woman at the base of her spine, is this to enable a person's arm to get in and apply resin and laminate to the seams of the final mould piece? How then is this hole not on the final cast? This really is a puzzle to me.
3. I want to use polyurethane or polyester resin for the cast, what is the best option?

Arrrrg, so many questions and options! Any advice and answers will be extremely welcome. I realise I will also need to experiment and test a bit with the moulding and casting prior to completing each process fully especially considering some of the materials will be new to me.

Thanks for taking the time to read this thread and I hope you can advise me further
Rob (Kent, England)
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  #2  
Old 03-14-2010, 04:20 PM
Andrew Werby Andrew Werby is offline
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Re: Moulding & Resin Casting - really need some good advice

Yes, you really should try something simple before launching into that major project, which sounds like it might be challenging even for someone with a lot of experience in mold-making. Why don't you make a one-sided mask or something similar in clay, then attempt the same mold-making procedures you're envisioning for your big figure? I'll attempt to answer some of your questions below:

What I understand is that Iíll need to create a bonded silicone, resin & fibre glass multi-piece mould.

[Bonded? What do you mean by that? The rubber part of the mold is (or should be) independent of the shell that supports it.]

With a hollow cast made up of a release agent, gel coat layers and then laminated resin layers using fibre glass mat soaked with resin, 4 layers of laminate for a two thirds life size sounds about right going on the above thread.

[While some sculptors like to make their mother-molds, or support shells, out of fiberglass and resin, this is not the only or easiest way to go. Plaster is much less toxic and difficult to work with, especially when making a multi-part shell. It's also much quicker. It's somewhat heavier and a bit more fragile, but I'd definitely recommend it over fiberglass to any beginner at moldmaking.]

Mould
1. What thickness should I apply the silicone rubber and should it be cured or semi-cured prior to adding the resin and fibre glass?

[You want to build up your silicone rubber to a minimum of about 1/4" thick; more is okay. It needs to be fully cured before you go on to the next step.]

2. Am I right in thinking the silicone mould will bond to the resin & fibre glass counter/mother mould?

[No; the good thing about silicone rubber mold compounds is that they don't stick to anything but themselves.]

If not then does the silicone mould just sit inside the counter mould? if so that means I have to make the silicone mould quite thick to maintain stability inside the counter mould which is something I want to avoid to keep my costs down.

[Sorry; if the rubber were stuck to the inside of the shell, there would be little advantage in using it over a rigid mold. Once you've filled the mold and removed the shell, you can peel the rubber off, making complex undercuts feasible.]

3. Does the resin and fibre glass need to be mixed together?

[Usually you paint on some resin, apply the fiberglass cloth, and then apply more resin to the back of it with a brush until it's saturated.]

4. What type resin and what type of fibre glass do I need, and also what type of silicone do I need?

[Since you're in the UK, the brands will be different from the ones we use in the US. But there are three basic kinds of silicone rubber.

1:Single-component types, that come in caulking tubes and cure by evaporation of acetic acid. This stuff is relatively cheap, but it contains adhesion-promotors that make it tend to stick to things. Also, it doesn't cure well in thick sections, has poor flexibility, and smells bad from the acetic acid. It is thick in consistency, though, and won't slide off vertical surfaces.

2 and 3: Dual component types, where one mixes a catalyst and a base, usually 1-to-10 or 1-to-20 by weight. These are what's generally used for making molds. There are two basic types, the tin-soap catalyst type and the platinum catalyst type. The tin-soap type is cheaper, but it doesn't last as long in the cured state. However it's also less finicky about contamination. The platinum-catalyst type works pretty much the same way, but it's extremely sensitive to foreign substances like oils or other types of rubber. If you use either of these, make sure you test it on your clay, with the same release and other procedures you plan to use on your project.

Polyester resin's about the same everywhere. Be very careful in dealing with the catalyst for it, though - it's highly corrosive. One drop in your eye, and you can start shopping for a glass one. The fiberglass cloth should be a light kind, since you need it to conform to complex curvatures - most is made for laying up on flattish surfaces, as in building canoes. Some people use loose fibers for this (but just thinking about it is making me itch...)]


Cast
1. Once the individual mould pieces have the gel coat and laminate applied how are they joined together? This really is a big mystery to me. Is further resin poured down the seams whilst rotating/rotacasting the complete mould? Or can individual limbs and parts on my sculpture made up of 2 or 3 mould sections be rotated separately which can then be attached to each other with resin and laminate?

[The reason you're making all those pieces is so the mold can be disassembled when it's time to remove the casting. Gluing them all together would defeat that. You have to plan your shell so that it supports the inner mold without any pieces of the mold being trapped when the inner mold is filled with hard material and won't flex any more. You can make separate molds of various pieces and attach them later, if casting the whole thing in one piece is unworkable for some reason.]


3. I want to use polyurethane or polyester resin for the cast, what is the best option?

[Polyester is cheaper and it sets much slower. But it does have an exothermic reaction that can cause it to self-destruct if the catalyst/resin ratio is a little off for the volume you're attempting. Urethanes tend to set so quickly that you don't have time to mix them thoroughly before they go off, but there are some formulations that are slower than others - try to find them to save yourself a lot of grief. I haven't seen Ron Mueck's videos, so I'll leave it to someone who has to address your questions about them.]

Andrew Werby
www.computersculpture.com
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  #3  
Old 03-15-2010, 06:52 AM
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fritchie fritchie is offline
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Re: Moulding & Resin Casting - really need some good advice

I'm glad Andrew got to this before me, because I've never used fiberglass molds, though I always use polyester rubber.
Those all are very technical questions, and my main question is - do you really need so many pieces to your internal (bendable) mold? One of the main reasons for using bendable internal molds is that this material, cast thin enough for flexibility but thick enough to resist tearing on removal, can be peeled away from tight bends to reduce the number of mold pieces. To do that, choose your dividing lines strategically. It should be possible to cover several internal pieces with a single, larger external shell this way.
You should add "bumps" or "tracks" to the flexible pieces so they will be held firmly by the shell if this is done. Of course, you must have registration marks in the internal and external mold contact edges so they will meet correctly when assembled. Another significant question is whether you expect the sculpture to be cast in one or several pieces. Most foundries probably would cast pieces and weld them together, grinding any misalignment later.

I do recommend molding a smaller figure first to learn.

Last edited by fritchie : 03-15-2010 at 06:58 AM. Reason: further clarity
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Old 03-15-2010, 09:28 AM
Rob_Rob Rob_Rob is offline
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Re: Moulding & Resin Casting - really need some good advice

Hi guys thanks for taking the time to read my thread and for your input its going to be really helpful to me, its information I wouldn't otherwise be able to get so I really appreciate it.

As to the cast I'm going to cast it in resin using laminated layers, I understand the mould needs to remain separate although I like the idea of using less silicone pieces and just have the mother mould as the 20 to 25 pieces.

I was wondering about the silicone bonding to the resin, I must have misunderstood the video

I also really like the idea of using plaster as the counter mould, I've already made three small portrait resin casts using silicone and plaster for the mould albeit they are only 2 piece moulds not the mammoth 25 I think the figure could need.

Anyway I think what I'll do is going on both of your adivce is to seal the clay sculpture with shellac a la Mueck, test a 2 piece silicone and and 4 piece plaster mould out on one leg and see how it goes. Then I will attempt to not ruin the rest of the sculpture and finish off the moulding. Then I'll cast the figure in pieces and join together as outlined in my first post which I hope is right. I might even make the legs solid to act as a good platform for the rest of the hollow form.

Fingers crossed this will work, if it does I will be sure to post the results and if it doesn't work I'll update this post also outlining my errors and hopefully some solutions.
Wish me luck I might well need it!
Rob
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Old 03-29-2010, 12:48 PM
KLRON KLRON is offline
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Re: Moulding & Resin Casting - really need some good advice

Are there Mold workshops out there that are at least one to two weeks long? The workshops in our area are 2 days max, and I do not think they go into the depth needed to really learn about the mold making process. I live in the Washington DC metro area. Thanks.

Kris
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Old 03-30-2010, 02:43 PM
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Mold Man Mike Mold Man Mike is offline
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Re: Moulding & Resin Casting - really need some good advice

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