Paper Pulp and Plaster in the Silicone Molds

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After a whole lot of messing around, I finally found something that works well in the silicone rubber molds I made several weeks ago. But we probably can’t call it paper mache. Oh well – I’ve never been much of a purist, anyway.

In the last two weeks I tried just about every combination of ingredients that I could think of. I told you in my last post, about the molds, that I thought I had a formula that would work well, but it turns out I was wrong. The goo captured details really well, but it took forever to dry. And then when I though it was finally dry enough to remove it from the mold, I would inevitably ruin the nose or the eyebrow – whichever part was lowest and collected all the moisture.

Last night I was about to give up, and then I remembered a series of experiments that Jonty, over at Darkside Creations, has been doing with paper pulp and plaster. He shared his results with the Yahoo Papier Mache Art group. (If you haven’t signed up for the group yet, you definitely should). He said that plaster and paper are fairly strong – if I’d been paying more attention, I could have been painting wolves and other critters several weeks ago.

So, as it turns out, the easiest and least expensive “formula” is the one I’ve decided to use for my series of decorative masks. As of this morning, I finally have some pieces that I can finish. The garbage can if full of rejects.

There are several reasons why I decided on this method, but I know it is somewhat fiddly. It will work for my project, but it might not be the best method for whatever project you have in mind.

My criteria were very specific – I wanted pieces that were fairly lightweight but strong, and that could be said to consist primarily of recycled or natural materials. I also wanted the pieces to come out of the molds fairly quickly so they could dry from all sides. And, although I don’t have a big show lined up or anything like that, I wanted a method that could be geared up for production, if I ever did decide to show them. Not that the world will be clammering for decorative hippo masks anytime soon, but that’s just the way my brain works.

When I reread Steve’s suggestion about layers, I realized that I could use paper strips and paste to add strength to the back of the pieces, so the front, the part that actually captures the detail in the mold, can be very thin and not terribly strong. What I’m ending up with is a sandwich consisting of a paper/plaster front, a layer of cheese cloth to add strength to the “skin” so it can be safely handled, and then several layers of brown paper and paste on the back to give the pieces their needed strength.

I don’t have the backs done on any of the pieces yet, but there’s no reason that I can think of why it won’t work just fine. Paper strips and paste are extremely strong when they’re dry, and the paper/plaster skin should be a nice surface to paint. So – here’s how I did it. (Please remember that you should do your own experiments before you decide that this is a good idea for your own projects.)

The formula:

1/2 cup cold water

1 cup Plaster of Paris

1/4 cup damp paper pulp

Adding Plaster to Cold Water
Adding Plaster to Cold Water

Measure 1/2 cup of cold water into a bowl and then put the 1 cup of plaster into the water and allow it to soak for a minute. While it’s doing that, you might want to go get a plastic bucket that you’ll need when you rinse out your bowl. Remember that plaster will get hard even under water, so you can’t rinse out the bowl in your sink.

Stir the Plaster Until Smooth
Stir the Plaster Until Smooth
Add Paper Pulp and Squish It In by Hand
Add Paper Pulp and Squish It In by Hand

You don’t want to use a mixer with plaster, because mechanical mixing causes the plaster to set up faster. You only have about 5 to 8 minutes as it is, so you certainly don’t want the plaster to get hard any faster than that. This part takes a bit of practice, and you might need to leave your pulp a bit wetter than usual.

When it’s all mixed, you can put the plaster/paper mix into the mold and spread it up the sides with your fingers or a small brush. I didn’t want my camera coated in plaster so I couldn’t get a picture of that part. I made my “skin” very thin – just enough of the mixture to capture the detail.

When the plaster is still wet but just starting to thicken, I placed a piece of cheesecloth over the plaster and used my brush to press the cheesecloth into the mixture.

Pressing the Cheescloth into the Plaster/Paper Mixture
Pressing the Cheescloth into the Plaster/Paper Mixture

I don’t know if the cheesecloth is really needed, but it seems like a good idea. I want the shell to be strong enough to hold up while the paper strips and paste are applied to the back.

The extra cheesecloth was then folded over, to reinforce the edges. By now the plaster will be starting to set up, and the shell can be removed from the mold in about half an hour. I’ll leave the pieces in a warm spot overnight to dry before finishing the backs.

You can see in the photo below that the plaster catches even the tiniest details. It also catches any flubs that might have been in the clay original, of course. (I forgot to add texture to the wolf’s eyebrow, for instance. Oh well, we can’t be perfect. There are a few spots where air was caught under the plaster, and I’ll repair these with paper mache clay.

Wolf Shell, Showing Eye Detail
Wolf Shell, Showing Eye Detail

I now have the shell of one hippo, one wolf and one mountain lion drying. The paper/paste backs will also take several days to dry, of course, so I won’t be able to start painting until next week. That gives me time to play around and make some more originals – it will be nice to get back to creating something again.

62 thoughts on “Paper Pulp and Plaster in the Silicone Molds”

  1. Lately I have been using a new method for casting in silicone molds. I use the regular paperclay and substitute Sheetrock Brand East Sand 45 joint compound. The kind that mixes with water. {here in California I buy 18 pounds for under $10 dollars from Lowe’s Hardware ] I use it like this. First I mix up a batch of paperclay. Than I mix up SEPARATELY an equal amount of the Easy Sand 45. After that I mix the paperclay and Easy Sand together. I find that the Easy Sand is about as hard as plaster but it gives a 45 minute working time. There is also a Sheetrock Brand Durabrand 90 which gives 90 minutes and is supposed to be moisture resistant once it dries. Also for the same $10 dollars I can get 25lbs of Durabrand instead of the 18 lbs of Easy Sand. The only thing is that I haven’t tried the Durabond 90 yet.

      • Hi Jonni
        I use your paperclay recipe like this
        2 cups blended paper towels [strained thru cloth but still wet]
        1 cup Premium Drywall Joint Compound
        1/2 cup Elmers Glue All
        1/2 cup flour

        Put that mix in a container, mix together, and take out what is needed. Than mix up separately an equal amount of the Sheetrock Easy Sand 45 in a separate container. Than mix in the paper mache clay and paper clay together. Than press it into the silicone mold. The use of the Sheetrock Easysand 45 gives you a lot of reliable working time. After about 1 day the mix will get hard enough to gently remove from the silicone mold.
        I have used both Smooth-On Rebound 25 and Smooth-On Dragon Skin 10 medium. I find that the Dragon skin is very soft which is great if you have undercuts and there is less chance of destroying your casts, when removing them from the mold. The dragon skin mold is very soft and must be thoroughly backed up with a plaster mother mold. To make my Dragon Skin silicone mold I brush on layers using the their thickener and alternating color additive. {red and blue} Uncolored dragon skin is clear.

  2. WOW! You Rock It ?
    Is this only way to use to cast paper pulp or Jean fabric pulp can l use like l use to make paper strong is mod poge type glue into the mixture can l do this will it gel set up?I like feed back 1st time be back .?as viewed your staying creative & hopefully prosperous let 5he adventures continue.?????????????

    • There are some videos on YouTube showing how a company in Mexico makes large animal sculptures in molds. I think they’re using recycled cardboard. They don’t explain it very well, but it does show us there are other ways to use the molds to make a paper mache-like sculpture in silicone molds. I’m sure there are lots of other ways, too. I made a few changes to the method, which you can see here, and another reader recently emailed me to say that she tried the paper pulp and plaster recipe and added a small amount of baking soda. She said it will give you a lot more working time.

      I have never used Mod Podge, so you’d need to experiment to see if it would work. Have fun with it! 🙂

  3. Reese and Jonni

    I forgot to mention. For the freezing process I used Sculptamold. Most paper mache clay uses PVA glue and Joint Compound both of these are supposed to be negatively affected by freezing. So if you want to use paper mache clay than it would probably be a good idea to substitute something else for the PVA and Joint Compound. Such as starch for the PVA and flour and/or plaster for the joint compound


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