New to resin casting, Q's about silicons and release agents

[cyberkid]

So, I've finally decided to take the plunge and start resin casting. I currently have no experience with casting at all.. I'm hoping to buy most of this stuff in person and locally.. since I'm not too sure I'll be casting that much. (I live in Asia... and just the shipping would cost me around 30 bucks for a basic caster's set)
My questions:
1. HTV? RTV? I've read that most people use various types of RTV, but I also see various forms of HTV. I have a dehydrator that does around 40-50c, not sure that's enough though. Any specific serial numbers I should look for? IE: RTV-533 etc? I'm looking for one that will give me decent detail without using a vacuum/ pressure pot.

2. Release agents: I've already bought a Gunze super hei cast resin mix set. Does anyone know if this needs a release agent? (My LHS said no... but he thought RTV was a brand )

3. Shelf life of resins and silicons? (Nothing is mentioned on the Gunze cans)

Thanks^^
Steve

[008]

Too much info to type up, but in general 10:1 mix RTV will require vacuuming and 1:1 mix RTV will not. However, 1:1 will break down a lot sooner from the heat of the curing resin.

Check out other forums, such as Alumilite's or the moldmaking forum under the "metalwork" section on CNCZone's forums.

[hirofkd]

All silicones I've used are RTV, so I can't comment on (1), but

(2) Hei-Cast is one of the best ones I have used because of its anti-bubbling nature, but it contains hazardous substance, so be careful. (Heisen Yoko also has non-Xylene type.)

Usually, you don't need any release agent between silicone and resin, especially when the surface of the master is smooth, and also when the model is still new. What happens is, resin generates heat, and it eventually deteriorates the silicone's surface. Then the cured resin begins to bite the surface. In order to extend the mold life, people usually use release agent. The durability depends on the brand of resin, silicone and how many times (or how often) you use the mold, so it's very hard to generalize. In my experience, a mold can be usable for making as many as 30 copies, but I noticed a rapid deterioration after 50 copies.


(3) Hei-CAST is one of the more durable casting resin I've used, but I don't remember exactly how long it lasted. In any case, I wouldn't trust the resin that's more than 6 month old. It attracts moisture, and the moisture causes bubbling. There are de-moisturizing additives that you can mix with resin to suppress this effect, but the effectiveness is limited. I know it will NOT work on 1-year-old resin. (Yes, I tried...)

[008]

Old resin that's saturated with moisture is quite a sight when cured. It looks like one of those lava rocks with all the holes in it. One side of the resin gets crusty as it absorbs moisture; just don't use the crust and you're good. The other half looks the same so you'll never know. I've been told by one supplier that you can boil out the moisture by either vacuuming it at 29"hg or putting it in an oven for a few hours. I'll try both methods eventually as I still have a half gallon container that I'd hate to throw away. I mistakenly thought I could save money by buying the larger container. Now that I have a supplier about 2 miles away I'll never buy more than the 1lb kits at a time.

As for silicone shelf life I've found that the activator eventually deteriorates and turns into a water-like substance. Haven't tried old RTV with new activator yet though.

[cyberkid]

Thanks guys much appreciated!