Problem with POP leaf & silicone

20 years ago

Hi Gang!

This past fall I made a POP mold of an elephant ear leaf and just this week got around to trying to make a silicone cast of it. What a mess! The silicone refused to stick to the surface. It peeled, it balled up, it came up in large globs, you name it-it did it.Then it started pulling up pieces of POP and ruining the mold. It was like working with glue. I had to throw the whole thing away! So frustrating.

Now I'm trying to figure out what I did wrong. Has anyone else had this or something like it happen to them?

I checked the exp. date on the tubes of the stuff, it was '07 so I figured they were good. I used a dry paintbrush and brushed the mold to remove dust. The weather was good, not too humid or dry and the temp. was fine, about 73 degrees. I was working in my garage with the door open but not in direct sunlight.

What did I do wrong or overlook? Or is this just a rite of passage and the next one will be fine?

Help! I don't want to repeat this fiasco.

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Comments (5)

rockhewer
20 years ago
hello nmgirl, Well there are several things you may have done differently. Some questions for you though.

1st, Was your POP mold sealed?
2nd, did you use a release on your sealed POP mold?
3rd, was your silicone 100% silicone?
4th, how thick did you apply the silicone?

Silicone generally will only adhere to itself, but it needs help to come off cleanly from a POP mold. There are several threads posted on this forum that go into some detail about this process.

Let us know your complete process and we can help you a bit better.
User
Original Author
20 years ago
1.I don't understand what is meant by "sealed". Can you clarify?
2. Yes, I did use a release agent.
3.Yes, it was 100% silicone.
4. I tried to put the stuff on no thicker that 1/4 of an inch.
I thought I had read the threads enough to understand the process but it seems I missed something.
And the POP mold was so nice too, I was very happy with it.
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rickharmer
20 years ago
Try diluting your silicone with a few drops of glycerine.This makes it more malleable.Check back in the posts for a complete story by Nobu.I believe it was 5-6 drops of glycerine to the ounce of silicone.
Give it a try!
Regards
Rick
rockhewer
20 years ago
Sealing is putting a barrier on the POP. A spray shellac or my favorite, spray laquer(both are clear), are good sealants. They dont need to be sprayed on, it's just convenient.

POP is an extremely porus material and will soak up any liquid thirstily. Silicone is a liquid that cures faster the more humid the conditions are. Since POP is is so porus it has moisture in it all the time even when seemingly dry (so does wood). So unless you have a even coat of release on the POP it seems the silicone would have bonded to the plaster because of the moisture in it and insufficient release.

Thus sealant would be that barrier there to keep the release on top of the POP. If the sealant coat is good enough use of a release agent may not even be needed. Silicone tends to stick only to itself. It sticks to unfinished wood because it gets into the pores and the moisture in it. That'd be true of anything unfinished. Try a dab of silicone on plain paper and a finished magazine cover, you'll see what I mean. It will peel easily from plastic or a countertop or bathtub too.

So by finishing/sealing the POP you'd be making certain the silicone would not stick to it.
User
Original Author
20 years ago
Thanks rockhewer. In reading up on this I either brain bubbled the part about the sealer or, I suspect, I rolled sealer and release agent into one thing. Big oops.
I'll try again this summer when the leaves have returned.
Thanks for your help.