silicone setting too fast.... anyone experience this?

[JOATRASH FX]

Hey guys

Thought I might start a new thread for this problem. I was mixing up a batch of RTV tonight to make molds of my Jubal Early pistol parts. I got a new digital scale to make sure my mixture was perfect. I know the usual problem is silicone not setting due to sulfur in the clay and all, but this is the opposite.

The RTV was supposed to have a setting time of 3 hours at the mixture I chose (and I followed everything to the letter since I haven't poured silicone before) but I barely had time to mix it before it went solid! It was the consistency of pizza dough within a minute. I could feel it stiffening as I was stirring. After about 15 minutes it was a solid lump. :wacko

Luckily it hardened so fast I didn't have time to paint any onto the delicate parts of the clay and model, so they're still ready for a new try. My guess is I got a bad batch or the wrong type of hardener/catalyst. I just thought I'd see of anyone else has had this happen to them.

 

[SgtFang]

Is your work area hot? Like 80 degrees or more? That'll kick it in a hurry. Maybe refrigerate your silicone, and mix in smaller batches?

-Sarge

 

[robstyle]

yup, heat and humidity play a big part with materials. I recall mixing 5 gallon batches and barely having time to pour it and thats with 12 hour set time stuff.

 

[JOATRASH FX]

Nope... not that hot. More regular room temp (it ain't summer here in Sweden any longer... :lol)

I only mixed up a small batch... 17 oz.

I gave it another try and used the bare minimum of catalyst, which is supposed to give a 24 hour setting time. This time I was able to apply a little before it went gooey. Now, about 30-40 minutes later it's almost set. There's gotta be something wrong with this stuff- you're supposed to be able to easily brush it on but it's like very, very thick syrup even before the hardener is added. If I brush it on so that it gets in the nooks and crannys and pushes out the air bubbles, I have to use so much pressure it damages the clay.

Anyway... it's almost six AM here now and I've used up all they sent me (I only got a third of the stuff I ordered :rolleyes). I'm gonna give them a call tomorrow in the morning anyway to find out where the heck my other stuff is, so I'll take this up with them too.

Thanks for the tips guys. Whatever happens, I'll try the refrigeration trick with the next batch.

Is your work area hot? Like 80 degrees or more? That'll kick it in a hurry. Maybe refrigerate your silicone, and mix in smaller batches?

-Sarge

 

[philippes]

What is the exact material you're using (e.g. brand, product number)?

Phil

 

[JOATRASH FX]

"Esprit Composite" RTV 181.

It's French... definitely not the stuff you guys usually use! We don't have any resellers for Smooth-on or the other usual brands around these parts.

Some technical data (probably says lots to you experts but not to me since I don't have anything to compare it with)

Viscosity: 35000 MPa
Hardness: 27 shore A
skrinkage: 1%
tear-stretch-factor: 380%


The funny thing is that the stuff is supposed to be so thinly-flowing that to apply it vertically you need to add a thickening agent called "tixotropt". I haven't been able to get hold of the right person where I bought it yet (the one who is familiar with casting processes wasn't there today) but another batch is on the way and I'm gonna shoot them an e-mail.

The second batch I mixed up seems to be curing, but I doubt I got anything even close to a bubble-free casting. The stuff was so gooey that I kept getting strands that looked like melted cheese stuck to the brush and they'd just create new air pockets as I went along. Later tonight I'm gonna back it up with some plaster and then we'll see how bad it is.

What is the exact material you're using (e.g. brand, product number)?

Phil

 

[Beagle Bill]

Maybe they accidentally sent you fast acting catalyst. I'm unfamiliar with your brand, but I know the Ultra Fast catslyst Smooth On makes can cure RTV in as little as 15 minutes. Hope you get this problem solved, I know RTV is too expensive to have mishaps. Good luck!

Bill

 

[JOATRASH FX]

That's my current theory. It looks like my second try might have produced usable mold-halves. I've asked them to send me some silicone thinner with the next batch. Hopefully,with that and cooling it in the fridge, it'll be enough.

Thanks again for the tips guys. :thumbsup

Maybe they accidentally sent you fast acting catalyst.
Bill