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I'm hoping that some of you who make your molds can help me out. I'm wanting to make some molds for some custom terrain peices in workin on. I'm looking at using resin to make copies and hopefully sell for some extra cash. I'm researching how to make the molds now. My question is about sealing and release agents. Since I'm on a budget is there something beside special products for sealing the items to e molded and for releasing the casting from the mold? Or do I even néed to do that?

The material I am looking at using is smooth on smooth cast 300.

Having made a few casts of my own with silicone molds, you do need to have some kind of mold release agent. While you are making the orginal as well as when you cast each piece. The stuff I have used is a simple mold release agent that can be brushed on. It is very simple and very thin and works well. I would recommend you look to whoever makes your resin or silicone to see what they have for releasing agents.

Good to know, thanks. I was hoping that there was something household wise I could use, but ill check out what the have as well. Thanks for the info my friend.

For the first half of the mould I just use spray on mould release which costs about £5 so, under $10. When making the second half of the mould I rub some Vaseline over the first half before I put the bits to be moulded in. The reason for this is that, not only does it help with mould release (ensuring the second half doesn't fuse with the first) it also helps to prevent silicone from seeping under the bit being moulded. Once the bit is in position then I give another spray with the mould release and that spray should last a long, long time.

When casting I use Talcum powder, the regular stuff you get for babies and just sprinkle that liberally over both halves of the mould, rub it in with a finger and then blow off the excess. I find that a good layer of Talc also helps a little with flow when pouring the resin.

If you are making chunky terrain pieces and want to save on resin then use some fillite powder. You can use a 1:1 of fillite to resin, sometimes even more and generally I find that adding a little just anyway also aides flow even if that might sound counter-intuitive. Fillite powder is really cheap and you get lots. You can get (at more expense of course) metal powders as well which are very nice to use as they give some nice heft to any bits you cast; great for bases and the like.

Where would I get filite powder at?

I got mine from the same people I bought the resin and silicone from. The company I buy from is called TOMPS but you should be able to find a similar product from whichever company you're using to get your stuff from; if they don't sell it though then send them an e-mail, these people are usually helpful with customer queries and they may be able to point you in the right direction.

Filite is likely a brand name as opposed to an actual material. I dont think I have ever come across the term.

There are a variety of fillers that you can use depending on what you want to accomplish. Glass micro ballons are common for just extending the resin...they also weigh less, so can help reduce weight for large items.

Other fillers can be used to change material properties, colors, and other choices for extending the resin. There is a limit to how much you can add though, as eventually there isnt enough resin to hold it all together.

Here in the US, Smooth On and Alumilite are the two big suppliers that are readily available.

http://www.smooth-on.com/Urethane-Plastic-a/c5_1119/index.html

http://www.alumilite.com/Category.cfm?Category=Support%20Products

Other companies will offer other fillers, and you can even buy them from unrelated companies.

Regarding mold releases, keep in mind that powders quite often retain moisture. Moisture is the bane of urethane resins, causing all sorts of problems. Liquid mold releases, sprays and what not, can often give more reliable results.

Thanks guys. I'm learning alot here.

I use common unscented talcum powder for filler on my PU casts. It changes the resin casts from a translucent to an opaque white, doesn't noticeably change the hardness or the mass or the flow/cast qualities (I use up to about 1/3 volume - you can go up to 50/50 filler with some resins).

Plain talc can be got from ceramic suppliers (it's a common ingredient used to make the liquid clay mix used for casting ceramics). You can also use the normal mild scented baby powder as well, and the resin locks it in, so you won't smell it anyway.

Ok guys. I made a couple small test molds using some 30mm markers I made for warzone. The two part plastic I used appears to work wonderfully. The ice silicon stuff I'm using for the molds has a ton of air bubbles that is males sing up the model being poured. Any suggestions on how to reduce air bubbles when making the mold?

One thing: pour from a corner and let the silicone find its own path over/around the original. Tapping it repeatedly helps. If you can build a shaker table it will really go a long way toward killing the air bubbles.

I've been doing the corner pour, it seems that the. Bubbles get it when I mix the two parts, it gets thick with lots of air bubbles. I tried placing the mold in a plastic bag and using a vacuum cleaner to try to use suction to draw the bubbles out but that didn't work either. I may try to build a shaker as you suggest, just gotta figure out how.

 Red_Starrise wrote:
One thing: pour from a corner and let the silicone find its own path over/around the original. Tapping it repeatedly helps. If you can build a shaker table it will really go a long way toward killing the air bubbles.

Like this: http://blog.kanojo.de/2012/03/28/quickhack-vibration-table-for-resin-casting/

(I think this is based on a spanish blog tutorial but I could not find that one.)

Shaker tables need a fair amount of time to remove bubbles, most RTV silicones do not always give that much time.

Vacuum degassing works great, as does pressure (pressure not removing bubbles, just compressing them).

However, proper mixing and pouring can go a long way to solve the issues. Try not to stir in air. I use paddle bits in order to avoid the air being mixed in. The paddles are always submerged while stirring and the shaft is the only thing at the surface to get air in with...so it is minimal. If you are mixing by hand, focus more on folding as opposed to stirring.

Stirring will normally cause a vortice that sucks air down with it. Quickly folding the mix (pulling from side to side sort of) avoids this and as opposed to little bubbles, it creates large pockets of air that find their own way out.

When you go to pour, a thin pour (either stream or sheet) allows a lot of air to escape as well. Tripours help a lot with this, more expensive then Dixie cups...but worth it. Dont pour to fast though, you can catch air before it has a chance to escape. You can help things along by using a brush to cover your master with a very thin layer of silicone. Thin layers cant hold air well, so this ensures the area closest to the master is void free.

Thanks guys. Ill try that