From: Liquid Plastic Solutions (paul@liquidplasticsolutions.com)
Date: Fri Dec 12 2003 - 19:41:47 EET
Hey there list,
I've seen a lot of people trying to help in this thread and some of the advise is good and some is not so good or at least enough to lead to a less than desirable result. Here's my rules of thumb for using platinum cure (addition cure) silicone systems.
Try to avoid them if you can. I'm not saying don't use them, but unless you know the compatibility of what you're pouring against to your silicone choice you can be very disappointed in results.
The main substances that inhibit platinum silicones are Sulfur, Tin ( as in those used for Tin cure or condensation cure silicones) and amine containing materials. That means anything you may not be sure about could inhibit the cure of platinum silicone. I have even seen times where a person wearing latex gloves handled a part before it was molded and upon demold you could see where the fingertips touched the part because the silicone didn't cure in those areas.
With regard to the use of a barrier coat like PVA or the like, I have seen mixed results. Apart from the barrier changing the texture of the part to be cast, I have seen bleed through areas that result in uncured silicone and the subsequent sleepless night's trying to figure out what to tell the client or the boss.
Again I wish to reiterate that I'm not saying you should never use platinum silicones. They have their place. They are high quality, strong, and have terrific shelf-life. You can cast pretty much any kind of material you want against them without fear of getting a bad result such as in the case of certain soft urethane elastomers. I'm just saying that caution should be used when you plan your molding projects.
I just thought I'd put in my 2 cents worth
Paul Jaeger
Liquid Plastic Solutions
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