Silicone Molding question

TomBrend

New Member
I make silicone molds / casts / appliances pretty infrequently, but steadily enough that I keep buying the 2lb trial size of moldstar from smooth-on.

I was thinking about buying the 1 gallon / 16lb buckets, but I'm worried about whether the silicone will still be good after some period of time just sitting there. Anyone have experience using one-or-two year old silicone?
 
Silicone has a shelf life of about 6 months (see the label for the expiration date). Buy the smaller amount and use as soon as possible. If it gets too old it won't set. I learned the hard way by having to scrape unset brush-on silicone off a sculpture. The silicone was a year old. The sculpture was in wet soft clay and the silicone had the consistency of wet snot. In a time saving zeal I covered four pieces in the stuff. It added an entire day to the build.
 
shelf life varies for many reasons ranging from temperature, proper sealing of the container, and a gray area vendors generally lack focus on is the actual manufacture of the material itself. Vendors act as a reseller for the material, they buy in bulk then repackage the raw material into smaller amounts for retail sales. The "date" on the label is likely the repackage date, not the manufacture date. Some vendors will have material sit in a warehouse for weeks to months and ive even seen longer, before being repackaged for individual retail sale.

As mentioned above, only buy what you can use or if you know it will be used in the direct future.

From personal experience, I just used silicone with a manufactures date of 2009 with no issues. I did however use new catalyst. The consistency was that of peanut butter but thats what was needed for the project. The initial consistency was that of a thick shampoo. Another trick is to use some Vicure. Thats actually to "kick" the silicone to cure as fast as needed. Ive had instances where there was literally minutes to make a mold and have parts from it. Using Vicure will reduce the molds life so its not recommended for anything other than "RIGHT NOW" parts. But, as mentioned, it works well with old silicone.
 
In 2009 I bought a gallon kit of Smooth-On's Rebound 25. After using it a couple of times it sat in the closet for 2 years before I needed to make another silicone mold. When I used it in 2011 it worked perfectly. I'm sure everyone wouldn't have the same results but I tend not to worry about shelf life when I'm buying silicone.
 
I buy silicon by the gallon but it never lasts. I wish it wasn't so expensive!!
I have had urethane rubber go off pretty quick however, it seems like once you open it the clock is ticking so my guess is that your milage may vary.
 
They do (or did) sell can of something you can spray into the opened container to displace the air and give the silicone a little longer shelf life after you break the seal.
 
Smooth-On is the manufacturer... It has a 6 month warranty but platinum silicone, such as Mold Star or Rebound as was mentioned, generally lasts longer (though the 6 month warranty stands)... it is not uncommon to see platinum silicones last a couple of years as customers have mentioned. Tin silicones will adhere more towards that six month time frame.
 
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