removing hardend silicone from a rock (quartz?)

[hairy perch]

my grandson and i made a rock mold for a coyote habitat. we had rub ed the rock with petroleum jelly, then we had put 4 layers of silicone on the rock for strength. one day later we came back and the silicone was hardend. as we where gently taking the rock out of the mold we had ran into trouble, some of the silicon had stuck to the rock and we cannot get some of the peaces of silicon of... he try ed to peal it of and had no luck. any ideas?

I HAD CHECKED THE ARCHIVES WITH NO LUCK

[Doug Bridges]

Tube silicone? That stuff is glue. You can scrape it off or grind it off.

[hairy perch]

this is his grandson, Kevin. not grandpa, i told him i would like to do some work in his shop, so he told me that i could make a rock for habitat. i asked him how to do it and he told me to go on taxinet and figure it out for my self so i could learn how to solve my own problems. i watched a demostrati on on how to make a mold of a rock and the guy said to use 100% tubed silicone. i cant trow the mold away because i used like 10 tubes of it... PLZ HELP ME!

[Doug Bridges]

If the mold is stuck, breaking apart and torn, how can we help? You will have to cut, scrape or grind the rubber off of the rock. Sorry, but that's mold making. Tear it off and start over. This time have grandpa order some good silicone rubber. Get away from using tube silicone. Heck for the $40 or $50 spent on tube silicone, you could have purchased some SmoothOn Trial kits of Brush-on 40 or Rebound 25 and made a real mold from him.

Sorry dude, but that is molding and casting. I remember my first mold. I threw away $100 of rubber the first pass at it. Keep working on it.

[hairy perch]

thank you very much! i took a pressure washer to it and it came off and i still have the detail in the rock. ill suggest to him about ordering some of that stuff you where talking about.
Kevin-

[eagleriver]

remember, silicone will stick to silicone and theres some silicone in rocks naturally, use a quality release agent

[Doug Bridges]

Eagle, I think you mean "Silicon" in rocks, not Silicone. Silicone is a synthetic material, man made. And yes, silica (silicon dioxide) is used in the manufacturing of silicone.

Tube silicone is an adhesive, not specifically made for mold making. Silicone rubber is specifically made for mold making. 2 very different animals.

I also feel that anytime you make a mold from a rock you should use a mold release or an acrylic clear coat to seal the rock. Rock may contain materials that inhibit the cure on many silicones, especially platinum cure silicones. Sulfur is a major chemical that will inhibit curing. Something else to think about.

[Roadkill]

Rocks also should be completely dried, like oven dried so that the moisture locked up inside will not effect the silicon curing. water with tube silicon will actually increase the curing and bonding. Just something to think about. don't sel in the moisture with releases until it is dry. johnson's Paste wax works very good as a release on rock and stone too. I like to put one layer on, then use the heat gun to slightly melt it into the rocks surface, then take another layer and then lightly polish it after application. The silicon or other molding rubber will just come right off.

[JE]

Here in the UK we can get silicone remover for tube silicone, I am sure you will be able to get it over there also. It simply softens any hard silicone to a point that it can be peeled or washed off any surface. The remover we get smells strongly of citrus ?
John

[eagleriver]

Doug, you are correct, I misspoke, its the silica present in some rocks that the silicone sticks to. I once tryed to mold a glass sculpture and was shocked that the mold material stuck like glue to it, i never did get it all off. I would suggest a clear lacquer coat  on anything that may have silica present, followed by a release agent made for silicone rubber

[John Helm]

Use gasoline to remove hardened silicone - guaranteed. That's why silicone can't be used as carburetor gasket sealant since gasoline breaks it down.  I tried everything to no avail once until I found out about the gasoline.