"Have You Used Hard Polystyrene As Mould For Sculpey?" Topic

I'm thinking of capturing some cool SF-looking textures with Sculpey polymer clay:

So, given that …

> The melting point of High Impact Polystyrene (HIPS – stuff like disposable clear plastic plates and clear packaging and lids) is 464°F (240°C);

> And given that the oven baking temperature of Sculpey is 275 °F (130 °C); then

Theoretically, could I use the inside of a HIPS vessel as a baking mould for Sculpey? Or would such a technique chemically alter the Sculpey somehow?

Thoughts?

NOTE: I was initially thinking of using Green Stuff (epoxy putty), but I would have ended up using a lot. Polymer clay is a lot cheaper. Well, I have tons of it already in a bin and don't want it to go to waste.

Thanks,

Dan
TMP link
TMP link
TMP link

For Sculpey no, but for Durham's Rock-Hard Water Putty, yes. I use food packaging all the time as molds with putty.

Sculpey may be baked as low as 200 F and still be plenty sturdy; you just need to do it for a longer time (1 hour verses 15 minutes at the standard temp).

So it might work for you…

CC, looking at your pictures above I'd say the interesting shapes are on the outside but the insides might be smooth or a slightly different shape. I'm tired so maybe I've misunderstood, but if you want to capture the outside shape wouldn't you have to put the plastic shape *inside* the putty?

If that's the case, I haven't tried it yet, but I've considered using expanding foam filler inside thin plastic items to make them hold their shape. I had a notion to make some kind of dropship out of a plastic lemonade bottle with those little Actimel/DanActive bottles for rockets, and I thought this might be a good way to turn the bottles into solid but lightweight parts that I could glue stuff onto.

I don't know if it fits with what you have in mind, so I'm just throwing it out there.

Polystyrene becomes soft and flexible at a lower temperature than it melts, so that might be a problem if you are relying on the plastic to hold the sculpey or want to use it more than once.

You might be able to press sculpey into the shapes and peel it out without too much deformation.

I've considered using expanding foam filler inside thin plastic items to make them hold their shape. I had a notion to make some kind of dropship out of a plastic lemonade bottle with those little Actimel/DanActive bottles for rockets

I haven't tried it yet myself, but from what I've read, the expanding foam exerts a bit of pressure when it expands, so it may distort some thinner plastic packages. Something to test for before committing to it full scale.

I have noticed that Sculpey causes PolyStyrene to melt. So I have to be careful I don't set a glob of Sculpey on something I want to keep.

I sculpted some terrain bases for Wings of War with Sculpy last year with intention of using them as masters for moulding with silicon rubber. I added some extra details made from Evergreen plastic card and over a few days I found to my surprise that the uncured Sculpy had dissolved the plastic card where it made contact. Quite ruined the models and had to spend a few hours fixing things.

Agree with the expanding foam considerations. If you allow the foam to free form in at least one direction it will not warp your form; open top for example.

So if you are looking to make terrain pieces that are more sturdy than the thin plastic, the foam would work nicely.

Apply a layer of inert primer to the plastic first and the foam should bond to it and pop right out when cured.

The over the counter foams come in many varieties but there are the basic three…

single expanding…for no pressure seals like those along windows and door frames

double expanding…for general function and use

triple expanding…for large gaps

I would use the double or triple but be conscious of the expanding aspect so you do not waste material with over fill.

Have lots of molds ready to go so you can fill several at a time, again to minimize wasted material…fill one to the half way mark and go the next one, then come back after a couple minutes and fill more if needed or apply some aluminum foil to retard expansion and increase complex fill potential with a "back filling" action.

:)

28mmMan,

During the "back filling", will trapped air create voids on the structure's surface? If so, what do you suggest to prevent them?

Thanks,

Dan

Ditto that Sculpey and styrene don't go well with each other. Makes a melty mess over time….

Hmm …

Well, once the Sculpey cured (in the oven), the HIPS acting as mould would be peeled off.

There would be no further contact between the two.

Dan

Dan,

The backfill should happen with gravity in this case, but if need be a piece of cardboard covering most of the open space will force the backfill action and yes it will take care of your pockets…most likely lol.

If you are worried then I would start by applying a bit of foam to those questionable spots first and then slowly add more until it starts to expand.

Hmm ….

Now you've got me thinking again.

Could I carefully place a tapered "block" suspended in the middle of the foam, and end up with a rigid but hollow building?

ADHD Dan

Sure.

An easier consideration is to take a thin piece of board (with a couple 1"-2" holes to allow some pressure relief), like paneling, and then attach a plastic bowl open side down to the board.

This way when you secure it to the mold it will create a hollow.

Just prime the board/bowl, let completely dry, then prime again just before the casting…the new prime will act as a release agent and bond with the foam.

:D

Just a couple of disjointed observations here:

(1) The spray-foam you can get in shaving cream-like cans at the DIY store for spray-in insulation can exert enough pressure to warp window frames and make the windows jam; there's a warning about this on the can itself. The important point is that there's a variant that's designed to seal around windows and doors that is more flexible and doesn't expand as much.

(2) If you're going to go to the trouble of fooling around with mold release agents, forms to create cavities and what-not, you should at least consider using some proper molding material. Check out Smooth-On's webpage:

smooth-on.com

and their YouTube channel packed with molding and casting videos:

YouTube link

I've had the melting issue as well. I sculpt all of my figures with Sculpey (EXTREMELY cheap; I can turn out around twenty-thirty figures and some vehicles for around two bucks), and often accidentally leave it in contact with some bitz. It's a serious pain to clean up.