Casting and molding problem.
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Thread: Casting and molding problem.

  1. #1

    Question Casting and molding problem.

    Okay, hopefully the more astute out there can help me with this problem I seem to be having. I'm using Micromark's blue 10 to 1 silicone mold maker and for some reason when I cast something it looks like there are places where the piece or mold shrunk. I wish I could get a good pic of it, but unfortunately my camera is on the fritz and since it's light resin, it doesn't show too well. I've also been embedding it the piece to be molded in plasticine clay (slightly better modeling clay) if that's a factor. I brush on a bit of the mix then I pour the rest over, and these "swell cracks" are always fluid looking, so mebbe that's also factoring in? And It may also be the silicone stuff itself. I have no idea how old it is, as Dad got it a while ago for his train stuff and I don't spend a lot of time making sure it's consistently mixed. If anyone can help me zero in on what to fix, it'd be mush appreshiated!

  2. #2

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    I have very very limited experience, but most silicon or resin heats up a bit as it dries and can warp a mold that is too thin or not reinforced enough as it expands and then cools. That may be it, but again i have cast like 3 things in my time and 2 were pretty epic failures while one came out fine.
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  3. #3
    Superfreak!!! Dragonsreach's Avatar
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    Quote Originally Posted by Chrispy View Post
    I have no idea how old it is, as Dad got it a while ago for his train stuff and I don't spend a lot of time making sure it's consistently mixed.
    Two issues to address right there.
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  4. #4

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    Thanks all- I found out it's most likely my inability to mix the stuff thoroughly- so I got one of those hand paint stirrers with the pinwheel tip. Of course, this means I'm putting bubbles in the stuff and have to agitate it a bit to get them out. Last time I tried casting, I somehow got a leak- so it seems I'm having all sorts of problems this weekend.

  5. #5

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    Some clays can cause problems with silicone mold products causing them to not cure properly. Not sure if this is what you're experiencing or not.

    Its always best to avoid creating air bubbles in both your mold material prior to casting and the resin when you are actually casting a piece. Without the equipment to vacuum de-gas, or to pressure cast, you can pour your material slowly in a very thin stream from fairly high above the mold....at least as much as possible given the working time of the products you're using. This will get rid of many air bubbles as they are broken when the material flows slowly over the lip of the container you are pouring from.

    I've done a fair amount of mold making and casting (self taught), all with products from Smooth ON. I've used Oomoo 25 (50:50 mix by volume) and Smooth Cast 305 (50:50 mix and better working time) with good luck. Smooth on publishes a booklet on basic mold making that is fairly good. Read it, make a mold or two, and read it again. It should get a lot easier then. Hope this helps.

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    Quote Originally Posted by heavybolterbob View Post
    Some clays can cause problems with silicone mold products causing them to not cure properly. Not sure if this is what you're experiencing or not.
    Using clay with sulfur in it will cause problems. Try to find sulfur free clay. Micromark used to sell the blue Kleen Klay with their starter kits, but Kleen Klay has been discontinued.

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  7. #7

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    I've been using the Van Aken Plastalina Modeling Clay- I really can't find a yea or nay about sulfur being in it.. But, 'tis all for naught, as the end to this tragic tale begins with me forgetting to put mold release on the other half and it totally encased my original. After much cutting and prying, I was able to get it out- but the hands and necklace broke off and it's now scratched in places where the scissors (even the round tipped mustache ones I was using) nicked it. I may return to attempting to cast stuff in the future, but for now I'm done on this project before it gets worse..

  8. #8
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    If and when you get the bug to try your hand at casting again, I recommend products from a company called Smooth-On in the US. (Dunno where you are, sorry)

    For first time casting, their product OOMOO is easy to use. It's a simple 1:1 mix, doesn't require degassing, and has minimal bubbles in it (I usually don't get any bubbles in the mold).

    Their other products are mixed by weight, some require degassing equipment, some do not. I'll be trying some of them in the future.

    But you seem to have already learned the most important part, when you are making the mold, mold release agent is a must! And you need to follow the directions (number of coats, wait time before pouring) to the letter. Doing so will almost certainly result in a good mold and many successful casts.

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