WHY do you do POP? Why not cast your leaf in a cement sand mix, then make your mold? The POP is not outside durable, but the cement sand one is and you would still be able to get a very nice mold from it.
Dena

Dena. Let me share my opinion. I prefer to make leaf castings with POP. I get NO bubbles at all and the casting has ALL the detail of the leaf. They are gorgeous!! I have even mounted the POP leaf on a black fabric covered board and hung it in my house as a piece of art!!!! I have put silicone on these POP leaves, and gotten molds with hardly any bubbles whatsoever. HOWEVER, I have NEVER been able to do a direct cast in concrete and have no bubbles. They tend to have lots. I want the most perfect mold for my trouble, so I do POP first. This is why "I" do pop castings, and then make a mold from them.
#1...direct white portland casting. See the iddy biddy bubbles?????
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#2...direct POP casting...Looky... no bubbles!!!
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#3...Silicone mold made from POP casting. Only a few bubbles!!
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If I had made a silicone mold from the concrete leaf, I would have gotten a few more from the silicone, thus adding MORE bubble holes. This is why I do the extra step. BB

I am sorry, Serene, I did not address your question. My leaf castings in POP are only about 3/8 to 1/2 inch if small leaves. My 31 inch Elephant ear pop casting is 1 1/2 inches thick, with expanding foam put on the back for support. When adding more layers to the casting, the water is almost immediately absorbed, and it is a little hard to spread, so I spoon it on and very quickly spread a little, and spoon on some more. The POP stays damp for several days. When it is finally dry, you will know. It feels very different than damp, cold pop. I have done silicone even before the pop is totally dry. As long as it is firm. It should have hardened withing 10 minutes, tops. Good luck. BB

BB, thanks for the info. I put another layer of POP on top of the three day old still wet POP and it firmed up quickly. Once it set up, I flipped the leaf over and started peeling off the rhubarb leaves. Not one bubble. I'm so relieved that it worked. I've made silicone molds before so the rest of the project I think I can handle. I can't wait to make my first leave with the finish mold!

Thanks for all your help. This forum is great.

Serene

BB thanks for the great information and wonderful pictures!
Your work has always been beautiful.
Serene glad your POP leaf turned out so nice too.
Dena

Again,I'll agree with Dena about direct.I just did 6 broadleaf maples.I applied portland and silica sand(fine mesh)and used 100% admix,no water.I then filled in any pinholes(yep,there were a few)with clay,and cast in silicone(Nobu method).Turned out fine.And,again,more power to you for doing so well with POP.A friend was here this week talking about molding body parts with POP(and the cloth used in casts).She's had good success there as well.I daresay that POP would be,with reinforcement,a better medium to be in with larger pieces.But I'm only working on small leaves that are decorations for our mirror frames.Not big at all.Concrete works quite well here.
Cheers from here.

Hi you experts!!! Anyone know how to fix a broken POP leaf/ lol

I have never tried to fix a broken pop leaf. hmmmm. Seems it would be hard to do, since pop is a funny thing. What exactly are you planning to do witht the leaf? If you just wanted to save it for display, you could form a box larger than your leaf, pour in some pop, and place the leaf on top of the new pop and fix it so it is together nice and tight at the crack and let it set up. It will make a nice wall hanging. Otherwise, I don't know. Will white glue stick to pop??? Sorry, I just don't know. BB

I used super glue to fix a small thin 1 1/2 inch piece of pop that broke off my leave before I had a chance to make a silicone mold. The glue held the pieces together and the hair line crack I filled with additional POP using a fine tip paint brush. I blended the POP in and then sanded it. You couldn't tell where the piece had broken off. I was able to make the silicone mold. Although, when I peeled the silicone away the small piece I had glued earlier came loose. I glued the piece back on using the same method above. I'm not sure if this method would work on larger breaks/chunks.

Serene