Rebound 25 & Oomoo 25 refuses to cure on various surfaces

[Hip Cat]

I tried to contact Smooth-On directly, but they're closed for the day.

I'm trying to make a three-piece silicone mold out of Rebound 25. One of these pieces is made of Oomoo 25 because it just functions better that way. I discovered while making the mold that it wasn't cooperating with my cheap modeling clay from the dollar store. The Rebound contacting it was sticky and messy, and simply wouldn't cure to hardness, making the mold useless. However, I also found that this was the case for the Rebound contacting the Oomoo portion of the mold. So I broke out some Roma Plastilina modeling clay, which explicitly states that it is sulfur-free. I made a dip in it, and did a test of how well the Rebound cured when poured into the various hemispherical cavities. One for the clay, one for the Oomoo, and a plastic measuring spoon as a control. The Rebound refused to cure completely after four hours now (the demold time is 70 minutes) on the sides contacting both the sulfur-free clay and the Oomoo. What's worse, I found out that my Oomoo won't completely cure when contacting the sulfur-free clay either, even though it's fine when contacting my dollar store clay. I'm brushing against a deadline and I want to know what gives? They're both brand new, work fine on say, primer and urethane, and I precisely mix them to their 1:1 ratios at room temperature, but I'm still having these issues.

 

[PoopaPapaPalps]

Hmm, never had that happened to me before unless my stuff had expired or mixed improperly. My suggestion is do another small test and leave it over-night; I never mess with the stuff in 4 hours or less in case it hasn't fully cured yet.

Also, if you've not invested in Thi-vex, I recommend you do so if you want to build up layers or anything else. It also helps kick the silicone to cure faster when it's added.

 

[robn1]

I've had problems with Smooth-On platinum silicones not curing against paint, no matter what paint I used. It would cure through but the surface was tacky, but it cured completely if I leave it for 72 hours. Even the 6 hour cure stuff needed three days.

 

[PoopaPapaPalps]

You guys use paint on your molds? I never spray my sculpts with anything but mold-release, mostly for the fact that I have to reuse my clay and don't wanna sculpt with clay bogged down with lead paint.:wacko

 

[robn1]

My "sculpts" so far have been wood, styrene, Bondo, putty and lots of primer. A final paint coat gives the piece a smooth even finish. I've tried a number of different paints and they all cause problems with platinum silicones. I've settled on Mold Max XLSII and it's been fine, it takes 24 hours but it's better than 72.

 

[Hip Cat]

I left it overnight and it's still no better. I called Smooth-On and they informed me that this kind of clay is prone to contaminants that hinder cures, and that the platinum-cure Oomoo interferes with the tin-cure Rebound. That's pretty useful information, lol. Thanks for all your responses!

 

[trooper]

yep, you cannot mold new platinum silicone on tin cured, but you can mold tin cure onto platinum
same goes if your using ground up silicone ( from old molds) as a filler for new molds. I only use it for tin cured silicone because I grind both types in my old meat grinder.

 

[CSMacLaren]

I left it overnight and it's still no better. I called Smooth-On and they informed me that this kind of clay is prone to contaminants that hinder cures, and that the platinum-cure Oomoo interferes with the tin-cure Rebound. That's pretty useful information, lol. Thanks for all your responses!

What make/brand of clay is it? Maybe we should avoid it.

 

[cavx]

What make/brand of clay is it? Maybe we should avoid it.

Sounds like it might contain sulfur?

Also, to add what has been states, you can use air curing silicone on additive but might find adding additive silicone to air curing won't cure.