Alumilite RTV silicone hardened by itself!

[kaho]

Several years ago I started toying around with resin casting using silicone molds. I bought a carton of alumilite silicone base/catalyst and made a 2 piece mold. The results weren't as perfect as I expected, and the remainder of the silicone base/catalyst set were left away.
Today, I planned out another, smaller mold thinking to use up the rest of my silicone. I got the parts prepped, vent holes planned out, mold box installed, mold release(vaseline) applied, only to find out that my silicone didn't feel the same as 3 years ago.

The viscosity of the silicone was so high that if i put a spoon in it, it would stand by itself for hours. The silicone won't pour anymore, it virtually holds its own shape against stirring unless greatly forced. I almost broke the spoon thats included in the kit.

Does anybody know if the alumilite silicone has a shelf life, and is that the reason for its hardening? Is there anyway to undo its hardening? And if I must buy new silicone, is the old catalyst still usable?

I also tried the 2 part resin today. Those also changed characteristic slightly but they are still usable with some work.

Thanks in advance. Any expert advice is welcomed.

[klutz_100]

Sorry to hear that!

IIRC ALL silicone and resin has a shelf life - usually around 6-12 moths.

I am not surprised you have found something wrong after "several years"

I always buy in smaller portions just for that reason. It might be more expensive per kg etc, but at least I don't get to throw away 50% of a much more expensive pot

[mike@af]

I use Alumilite products all of the time and I've experienced the same. I buy large quantities of RTV and resin and have to use them quickly, but I have been able to extend the shelf life of my resin. For the RTV, it has a shelf life of about 6-12 months after its been opened. The catalyst will also break down and seperate during that time. Also as a side note, be sure to always shake the catalyst before making a mold because it does seperate after a couple hours.

Resin will also break down after a few months as well, it is usually side B that goes bad. Side B will usually seperate in the regular casting plastic, RC3 doesnt seperate. Also, humidity is a huge problem in storing resin as the moisture attacks it. I've been able to extend the shelf life of my resin by nearly 12 months by storing the gallons in a cold, dry (dehumidified) environment. When I close up the jugs, I closes them up very tight, sometimes with a set of wrenchs so no air/moisture is let in or out.

Hope that helps.

[D_LaMz]

well then I should probably start using all of my resin.

[SteveK2003]

I too have heard that silicone has limited a shelf-life, several years is definitely beyond that. Always order your stuff, don't buy anything that's been sitting on a shelf in a store unless you know it's 'fresh'.

I forget the brand but a guy at the LHS says there is some type that is supposed to be amazing stuff, but the shelf-life is only a few months, and you can only get it directly from the manufacturer because it's made to order. Probably pretty pricey too.

[OutaFocus]

Originally Posted by GTmike400

Resin will also break down after a few months as well, it is usually side B that goes bad. Side B will usually seperate in the regular casting plastic, RC3 doesnt seperate. Also, humidity is a huge problem in storing resin as the moisture attacks it. I've been able to extend the shelf life of my resin by nearly 12 months by storing the gallons in a cold, dry (dehumidified) environment. When I close up the jugs, I closes them up very tight, sometimes with a set of wrenchs so no air/moisture is let in or out.

Hope that helps.

Mike, you can use a molecular sieve to absorb the moisture. It pours right into the resin, but you need to use a strainer to keep it from getting into the parts. The nice thing about the product is it's reusable. You can use an oven to bake the moisture out. You can get it from several sources, but I got mine through Vagabond.

[kaho]

Sigh....

Just when I needed them the most.

I was thinking of making another set of rims out of the remaining silicone, but my life became too busy. Its all just bad timing.

However, I have been working on casting things using my old mold, and I DID IT!!





These come from the mold of Spoon Sports SW388/Rota Slipstream wheels I made 2 years ago. When I tried casting the resin kept hardening way before they fill up the entire cavity. This time I used another kind of resin which soft cures in 24 hours, so that I had time to brush a layer onto the faces of the parts, close the mold, and then start slowly pouring the remaining resin into the mold. I waiting a day to pull the part out. From the looks of it there are no bubbles formed on the face of the rims, but its still hard to see because the resin dries translucent.
48 more hours until I can actually work on cleaning it up. =)

[NOMADGAMER]

normally clear resin is almost twice the price of ivory or white.

why are you casting in clear?

p.s. those spoons look great, cast me a set.

[bvia]

Good job!...and yup, a super low viscosity/slow setting resin is the key to being able to cast bubble-free parts without a vacuum/pressure pot.

Bill

[kaho]

I didn't know the difference in color has a price difference, I didn't have much choices when I bought it because the shop sells this and the other one that takes about 5 minutes to cure, and I found out the fast cure resin doesn't work well for me. I bought this clear resin for about $20.
Nowadays I can't even find silicone mold maker in the city where I live! My project is forced to be delayed!

I cleaned up one wheel. It was a PITA to get the flash out of this set. Some sample installations:




Anybody who lives in Calgary knows where to get more silicone RTV mold maker?