I meant to do this some time ago, but here is the result of my little experiment.
The problem: silicone can be very heavy and bounces back into position when it is quite thick. There is a silicone foam available (Soma Foama) but it is very expensive. Using cushion foam to bulk out a puppet and then putting it into a mould with silicone just results in the silicone being absorbed by the foam, making something even stiffer.
Solution: bulk out the puppet with cushion foam, then coat it with builder's glazing silicone. I have used Dow Corning 799, and it works well. The builder's silicone is very thick, so it does not get absorbed by the foam. It is possible to apply it with a spatula to get a thin coat which is very flexible. It does not inhibit platinum silicone. I have used it behind eyebrow paddles so they can move more freely, and it works well.
Here's a photo of my piece, which remains light and squashy.
Hi Simon, that is very interesting. Now will you put that piece in your puppet mold and pour your regular silicone (Platsil or whatever) around it? And the puppet silicone should stick to the glazing silicone without soaking into the upholstery foam because it's sealed, right?
Great experiment! Thank you for sharing. Please post a photo of the final puppet! Cheers.
Hi Dawn. That experiment was not intended for a puppet, just to prove to myself that it works. I had some spare Platsil that I put over the builder's silicone, and sure enough it doesn't soak in. The Platsil will peel back from the builder's silicone, but you have to pull it, so for most purposes it should be fine, and a little physio wrap would help to anchor them if concerned.
Where I think this will be most useful is in casting a complete torso in silicone. The abdominal area needs to bend and having a great chunk of silicone there would be heavy and solid. So by trimming the cushion foam to allow a skin of silicone, then trowelling on the builder's silicone as a sealer (it can be tinted if needed), it should permit a reasonably lightweight section. I have a puppet I want to do this with, a muscular blacksmith, but I haven't started sculpting him yet, so it might be a while. I was particularly thinking of Nick's problems he had with a sumo wrestler, and this might be useful for that sort of puppet. The silicone skin won't crease and bend like latex foam, so that will have to be considered.
I am also using it for eyebrow paddles, and have one almost ready to go in the mould, so I will post a pic when that is on its way.
It sounds like you have discovered a great technique for a lightweight torso or anything with a large mass that needs to remain flexible and retain the beauty of silicone. Again, thanks for sharing and I look forward to your progress.
That would have really helped when I made a silicone Sumo wrestler! I tried cushion foam, as I do with foam latex, and the silicone did indeed soak in and it was even stiffer than the silicone by itself. I re-cast without any bulky cushion foam, just some wrap on the armature to help the silicone stick to it, and I also used 3 wires in the spine instead of 2, so it worked well enough, but was heavy. the foam wrap on the builder's silicone sounds like a good solution to the non-stick issue.
I recently made a partial mold, from silicone caulk, of the face of a sculpt i'm working on, then melted Monster Clay into it so I had a replica. Anyway, as I'm new to using silicone, I was worried that my original sculpt would cause problems when making a platinum cure mold, due to using caulk on the face, so I did a test on the face I cast from the caulk mold, and the platinum silicone cured fine.
I'm almost done working on my sculpt and will be molding in platinum silicone and casting a stop motion puppet in Ecoflex-30, so I'll be testing out the sponge and caulk method within the next few weeks.
I'll report back with the results. I do worry about it having the "rubber boot" effect, but maybe the foam wrap will give enough grip?
Also, apparently you can get rid of the vinegar smell by kneading the caulk in water with dish soap, it also takes out the tackiness, and then you can use your fingers to smooth the caulk over objects. I've not tried this, but have used dish soap and water directly on my fingers and it does stop the caulk from sticking to you.
Hi Lee. It would be good to see how you get on. I suggest trying the builder's silicone on a scrap of foam, then putting some ecoflex over it, like I did, to see if the grip is sufficient. It will help to leave the surface of the builder's silicone rough for grip.
I have been using glazing or neutral cure silicone, which does not give off acetic acid. So clearly both types work fine. Have also been able to give the stuff a decent smooth finish by using powder on my fingers when shaping it.
Bit of an update on the caulk/platinum silicone curing:
I tried out coating some foam with silicone caulk. Now, the first attempts stayed tacky, even after 24 hours. I tested it on one of those dish washing sponges (the sort with the scouring pad on the top) and also did notice that the smell of that caulk was lingering for over a week (I made a mold from it last week). Anyway, I opened another tube of caulk today and tried it out on some soft PU foam I had bought off ebay (the stuff we use for build up puppets) and let it set, then applied some platinum cure silicone to it and it cured fine. I did change the mixing cups too, as the first ones had colour on the outside, so maybe the plastic had been treated with some chemical? So went back to using the clear mixing cups. Anyway, something out of that lot...... mixing cup, strong smelling caulk or the dish washing sponge, was inhibiting the cure, but it worked in the end!
Edit: I also used corn flour on my fingers instead of dish washing soap. Could be the Fairy Liquid soap that inhibited the cure?
The platinum silicone I used wasn't Eco-Flex, as I've not ordered that in yet (I had been debating learning how to run foam latex instead of using silicone). I used some mold making silicone (shore A5) and that has stuck really well to caulk.
I did see a video showing a method to get silicone to adhere to expanding foam, so maybe it would work in this case, too? Basically, they were making a silicone mask, and on the second layer of silicone they brushed into the mold, they put cotton wool in there with it, so the fibers were sort of sticking out all over the place, then they poured in the expanding soft foam and it made a bond.
I'm glad it worked. Yes, it could be the washing up liquid. I am using icing sugar powder these days, as it washes off nicely and is non-toxic.
The silicone I use is the non-smelly type (glazing silicone) and it works well without creating the stink, so perhaps try that for your next tube. It doesn't cost much more.
I like the cotton wool for sticking the foam to. Will try that out too sometime. Have you got a link to the video?