Silicone curing on silicone / release agent problems

[Sevv]

Hey

I've read quite a few threads on this, in fact I posted one myself a few years ago but I'm back here with a similar problem.

I have made a clay bust, Chavant medium clay if anyone's interested For years I have used RTV silicone to make my moulds so for this piece I thought nothing different. I did a test piece however just to be sure as I knew I would be casting in silicone.

I tried to make a cast from my test piece in dragon skin fx pro. It cured but the surface touching the RTV was very tacky, no good, further research on here discovered RTV is probably a tin cure silicone. Haven't found out for sure but that seems the most likely. Dragon skin (platinum cure) doesn't play well and won't cure properly.

A recommendation from here suggested using Plat gel 10. Due to its much shorter cure time it stood a better chance. I tried it (new favorite silicone btw!) but unfortunately it still cured tacky.

I've tried (curiosity really) plat gel 10 on cured plat gel 10, not unsurprisingly it dried permanently. I tried using a release agent, Mann Ease Release 200, but unfortunately it still dried as if it was all poured as one. The release agent had no effect. I was pretty shocked the release agent had no effect. I haven't yet tried something like vaseline but id rather not as that might clog up all my skin pours etc

I really want to make a silicone mould and cast in a platinum silicone but using the rule off... plat won't cure on tin but tin will cure on plat... I dont see how I can *confused*

I have the option of making a hard mould of course but id love the option of casting both silicone and resin busts. You can't do that from a hard mould. Maybe I'm using the wrong release agent? I could make an RTV mould, hope I can get it off without causing damage to my sculpt and then make a hard mould... that's asking for trouble though

Can anyone help?

 

[mslz22]

How soon after did you try to cast the bust in the Dragonskin? Sometimes tin cure silicone requires a few days post cure or a slow bake to fully cure or else it is still "active" and can make resins tacky if cast into too quickly. I would assume that the same would go with any material cast into it, even Dragon skin.

The other thing i would consider is making your mold out of urethane rubber. I have a few projects that i have made silicone molds and cast in urethane rubber using Reoflex 40 dry and it works great with no release agents. It does not make a difference if the mold or the casting is the Reoflex, it works either way. I believe there is a brush on additive or application if you usually make your molds that way.

 

[Sevv]

Thanks for the suggestion mslz22, it has actually been a few days since I cast my tin cure silicone so I would imagine its fully cured at this point.

A urethane rubber mould is a good idea, I hadn't thought of that. Ill defiantly look into it. I did go to another local supplier at lunchtime today and they believe my release agent isnt the correct type. Ive bought some Formula 5 and been told it will work Looking forward to testing tonight.

 

[Mr Mold Maker]

As you've found out, platinum silicones will not cure against tin silicones. Sadly, there isn't much you can do to fix it other than trying to use Inhibit X, which will force the platinum to cure.

What you'll run into using Inhibit X is the platinum will want to bond to everything that it touches, so before applying Inhibit X into the mold you need to release it very well. I'd suggest Ultra 4, an epoxy parfilm, to release the platinum.

I've never used Formula 5 so I can't speak on how well it may or may not work, but what concerns me is what I've read says it's a silicone based wax. Some silicone based releases will actually promote bonding.. Nothing sticks to silicone but silicone rule applies with releases as well.

 

[Sevv]

Thanks for the release agent suggestion. I will try to get hold of some Ultra 4 and try it... definatly want the best tool for the job.

I tried Formula 5 last night and... it did work It wasnt what I was expecting but it did work When I have used release agent on two part RTV moulds in the past they have almost slid apart. Came apart very easily. Last night, if you didnt know it was in two parts you'd never have guessed. It bent in your hand as one whole piece of silicone. You really had to know where the join was and really get your finger in to start it off. As it came apart there was trememdous suction and 'stickiness' holding both halfs together. Dont get me wrong once started they did come apart without any problem and they were both perfectly cured on the inner surfaces \o/. It was just harder to get apart than im used too. Im guessing this is just how it is with this type of two part mould.

I am still going to do further tests before I go ahead and cast my bust. Ive spent too much time on it Im going to cast just the chin/lips etc to get a good sample of the texture ive put into its surface. My test last night was just a flat smooth blob. It will be interesting to see how much the release agent effects the skin pour detail, and how easy
it will be to get apart with a much more textured surface.

Interesting this... glad im making progress. Ill take a look at Mr Mold Makers suggestion this afternoon.

 

[Robot]

I can't offer advice on using plat to tin cure silicone, but if you want to use plat to plat without any problems use Royal Jel-E from fuse fx. I've made plat silicone negatives and poured plat silicone inside for the positive and it works like a charm. No detail issues, tacky issues or sticking, just make sure you use it as recommended.

http://www.fusefx.ca/products.html#royal-jel-e

 

[detenten]

I've cast Dragonskin in Rebound silicone molds with great success in the past. The only time I had cure problems was when I used too much Mann Release and didn't allow it to dry completely before casting.