Making Urethane Molds for Paper Mache Clay

Black-Footed Ferret, Clay Model
Black-Footed Ferret Clay Model, Being Sealed

This week I made three urethane molds of clay sculptures – a black-footed ferret, shown above; a walrus; and an Arabian Oryx. I intended to make a Caspian seal, but after it was done I decided a walrus would be more fun.

Arabian Oryx and Walrus Clay Models
Arabian Oryx and Walrus Clay Models

The other two models are shown above, after being sealed. The models were sculpted using water-based pottery clay. I allowed the clay to dry to leather-hard stage before making the molds. The ears of the oryx dried faster than the head, and I now realize I should have left them off the model, since they could be added after the paper mache clay was dry. Live and learn…

After the molds were done I then messed around with the paper mache clay recipe, changing it so it would be slightly easier to use in a mold. For that part of this project, I’m definitely still in the experimental stage, so any suggestions will be appreciated. I’ll show you what I’ve done so far with the clay recipe down towards the bottom of the post.

The clay models were sealed with a product called SuperSeal, made by the Smooth-On company. I ordered the sealer, the release, and the Smooth-On 40 rubber mold compound from Farwest Materials in Walla Walla. (They have great customer service). After the models were sealed, I sprayed on the universal release, and allowed the excess to evaporate. Then I mixed up the two parts of the rubber compound and brushed it over the models.

Adding the Rubber Mold Material
Adding the Rubber Mold Material

I allowed the rubber to set up to the tacky stage between coats. After four coats were added the mold looked like this:

Rubber Mold
Rubber Mold

After drying overnight, I made a support mold with plaster of Paris:

Plaster of Paris Support Mold
Plaster of Paris Support Mold

When the plaster was hard, I removed the clay model. The mold is now done. You can see that I cut the rubber mold at the ears, to make it easier to remove the finished piece.

Rubber Mold and Support Mold
Rubber Mold and Support Mold

Now for the fun part. I tried the paper mache clay recipe just as we normally make it, pressing it into the molds in a thin layer about 1/4 inch deep. There were two problems – the clay takes a very long time to dry because air can reach only one side; and small voids mar the surface of the piece where the clay doesn’t fill the mold correctly, no matter how carefully I pressed it into the mold.

For the first problem, I tried using a fast-setting joint compound to replace the regular product we normally use, but my efforts weren’t very successful. It seemed like such a good idea, but…

In the end, I came up with a variation of the recipe that seems to work, although I can’t give exact measurements. Lots of experiments still need to be done. I mixed up a small batch of wet toilet paper, just enough water to cover the paper in a small bowl, and Elmer’s Glue-All. This made a “soup” with a lower paper content than the normal recipe. I then mixed in some corn starch and some plaster of Paris. The corn starch helped the mixture stick together so it was easier to work with, and the plaster caused the mixture to set up so it could be removed from the mold fairly quickly. Obviously, with the plaster in the mix, I needed to work a bit faster than I normally do.

I used a soft brush to paint a thin layer of the mixture into the mold, and then covered it with about 1/4 inch more.  Using the brush and a thin layer helped reduce the number of voids on the surface. As you can see from the photo, the “clay” I mixed up has a consistency like whipped cream cheese. I mixed just enough for one mold at a time, and each mixture came out a little different.

Adding the New Paper Mache Recipe to the Mold
Adding the New Paper Mache Recipe to the Mold

The ferret and the walrus have now been taken out of their molds – I’m still working on the oryx. The plaster has set up, but they are still very damp, and will need to dry for several days. Then I’ll make the walrus’ tusks and the oryx’s horns, fit everything together, and paint them. I’m still not sure how they’ll be mounted – I definitely want to avoid the hunter’s trophy look. Suggestions?

Since the first pieces have not yet dried, we still don’t know how strong they’ll be. They’ll be hung on a wall so they don’t have to be totally unbreakable, but I do need to be able to move them around without worrying too much about breakage. I hope to have at least 12 different pieces finished so I can take them to an art fair at the end of August. You can see the plastic mesh that I’m using to reinforce the pieces below, under the ferret. I might also use some traditional paper strips and paste on the insides of the pieces to make them stronger, if needed.

Walrus and Black-Footed Ferret
Walrus and Black-Footed Ferret

I’m really looking forward to seeing the walrus and oryx with their tusks and horns. I originally intended to only design smaller items for the molds, like the ferret, that I could easily ship – but once you get your hands in clay, who knows what will happen?

As always, your suggestions are welcome. And if you’ve done similar experiments, please let us know how they turned out.

40 thoughts on “Making Urethane Molds for Paper Mache Clay”

  1. Hi there. I currently in the process of making a star wars helmet for my daughter. it wont be too long before I have a silicon mould made ready for casting. could you please give me some advice on if any of your recipes or tutorials would help make a sturdy, smooth helmet? thanks for any help. 🙂

  2. Hi all.
    My daughter wants to make a paper mache horse from one of her horse models which is made from a hard plastic.
    Would this mold making method work on a plastic model without harming the original?
    Or would there be a better way to do this?
    Model magic?

    Thanks

    J

  3. Hi
    I normally sculpt Santa doll with sculpey. I want to try to make plaster mold of one of them and make one in paper clay.
    is it possible to mold the paper clay in a plaster mold? Do I ah be to prepare the mold before? I was thinking to use a sealer in the mold before the molding is it good?
    Hope you understand me, my English is not so good….
    Sylvie , from Quebec

  4. Hello Jhonni! I made a paper mache cat according to your recipe and post your tutorial. But I want to keep it before selling to repeat the same. Do you have a recipe for making a mold. Should I protect my sculpture with a film before remove plaster or should I use a liquid solution? Thank you for your reply. cordially. Delphine

  5. Hi folks

    I am very interested in what you’re doing with paper mache clay. It seems like a natural progression from the old strips of paper and wall paper paste. I do lots of things for fund-raising and I wonder if you would give me the UK equivelant to ‘white glue’ and ‘joint compound’? I would have thought they were the same thing. The white glue may be what we know as PVA glue or wood glue, but what is ‘joint compound’ please.

    I love your ‘trial and error’ approach and your honesty. It’s ‘real life’ for those of us who are continually experimenting. I would appreciate a reply when you have time.

    Thanks for now. Sandra, North Yorkshire, UK.

    • Hi Sandra. Yes, the white glue we use is a PVA glue, so you should be able to use whatever brand you find locally. Several readers have told us that in the UK, the joint compound is called “joint filler.” Tell the guys at the hardware store that you’re looking for the mud that is used to fill the cracks between plasterboard on new walls.

      Enjoy!

      • Thank you Jonni, and your guests. One of the brands here then, is Polyfilla. I will have a go and let you know how I get on. Sandra

  6. Well, finally somebody has come up with a mass production mold that works with paper mache! Hooray for Jonni! – My very good brother, who so admires my creative side, has always had suggestions for me on how I could make some extra $$ with my hobbies. He has suggested exactly what you have done – to make a mold to mass produce my masks! So now that I have your secret, Jonni, naturally I will become rich by trying it, or something like that… Thanks for all of your wonderful, creative ideas that continue to inspire and excite all of us!!!

    • Excellent! (Well, I don’t know about the “getting rich” part, of course.) I can’t wait to see your masks. After seeing some of your other work, I know they’re going to be quite interesting.

      When you have some masks done and ready to sell, remember to check out my tutorial on building your own website. (I really need to come up with a better header graphic… Too lazy, I guess.)

  7. HI
    GREAT WEB SITE WANT TO MAKE A MOLD USING A FROZEN SALMON ABOUT 34 INCHES LONG . ANYBODY HAVE ANY SUGESTIONS ??? YES I WANT TO EAT SALMON LATER IF POSSIBLE IT WILL NOT GO TO WASTE THANK YOU

    • There are a number of videos out on YouTube that show people making molds, but I don’t know if anyone has made one of a fish. The urethane that I used for my walrus and ferret molds is not edible, so I don’t know if you can use it on a fish you intend to eat afterwards.

      Have you considered making your mold out of plaster? Does it have be detailed on both sides? What a project.

      Ideas, anyone?

  8. Hay Jonni.
    I was wondering if you are going to try and make a miniature 3-Dimention mold for say like the 12 inch figures???.
    As I was thinking of, when I have made a couple of my “Breyer” size model Horses, which are about 12 inches in height…I would like to try and reproduce some…=).
    I look forward in hearing from you…=)
    Sharon.

    • Hi Sharon. My mold-making experiment taught me one thing – when I know I can make more than one of any design, I lose interest in making any. The best formula is the easiest one – the paper mache clay using glycerin in place of linseed oil. It won’t give you a perfect reproduction, but the voids can easily be filled in with more clay.

      So no – I won’t be making molds for sale.

  9. I showed this technique to a friend of mine who is using molds. I mixed up a few batches for her. I use light weight joint compound and I included linseed oil in all of them. The variations were quantity of glue and flour. The mix that was the driest, in other words, had the most flour, worked best in the mold. It released well, dried evenly without warping and picked up all the details from the mold. This was during the height of summer in an unairconditioned house during a heat wave and high humidity. Go figure! If it works then, it will most likely just work. She is completely in love with this new medium. Thanks!

  10. Gads, I’m not even sure how I got to this site but sure did enjoy it and want to try the paper clay your showing how to make. My problems is a new server and changing pass words till I’m in la la land with not remembering what each one is. Trying to make them all the same and note books close to write it all down. All the comments here are really great and give lots of good ideas. For the background mounts I agree some sort of real life background the animal or subject would be great.

  11. just found this site..WOW there are other paper crazy people out there…am I happy!…family says nothing made of paper is safe in our home…I start looking at it and see a million things…anyway my question is have you ever worked with Sculpt-a-mold?….I use it in molds as well as free form….it’s handy because it can dry fast….has plaster in it….meanwhile today I’m back to the “real” thing as I want to make a ball base piece..hope everyone has had a look at the newspaper by now!…..oh I’m putting this at the top of my FAVORITES….now I have other people to talk mache with…Yippee….melissa

  12. Looks like you have many devoted fans out here! Going on with my question seems like old news now. I did measure out the paper after I squeezed it, but only used 1 1/4 Cups of the TP. One potential problem there. Also, the joint compound was premixed, but it had quite a bit of water on the surface when I opened it. I tried to mix it back into the compound, but it is also possible that I didn’t do a very good job, so another potential source of the wetness. I added a couple of tablespoons of flour to my clay and it helped a lot, but was afraid to go any further in case the flour threw off the sculpting abilities of the finished product. After reading your article about the molds though, I can see you really are able to play around with the formula quite a bit, so I might get brave and if nothing else, use this batch as practice until I get it right.
    Thanks for your continuing assistance!
    Ann

    • Hi Ann. Yes – you can play around with the recipe and find the combination that work best for you. When you do your experiments, if you discover anything interesting, please let us know!

  13. Thanks Jonni, this is great. Using moulds is something I’ve been thinking of having a go at for quite some time now. This tutorial has given me the kick in the pants I needed to actually have a go.

  14. They look great! Funny timing… I just bought a Smooth-On Mold Making & Casting Starter Kit. I have been holding off using until I come up with something worthy of duplicating. Can’t wait to see what you come up with next.
    P.S. I hope your book is giving you some extra money to play with. Who knows what you might come up with next. 🙂

  15. I’m enjoying reading this technical feedback! 🙂

    On the how-to-mount issue, these are more plaque-like than bust-like, almost high-relief. I like the idea of flush-mounting them to a plaque/tile with some other texture or artwork. I like the idea of mixing the media and approach in one piece.

    Jonni, since your models have less surface texture detail than your other sculptures (fur, warty hair follicles), is this something you might add on to the molded paperclay before painting, or do you intend to keep them smoother? Maybe suggesting surface detail in your paint/stain?

    Really looking forward to seeing horns and tusks!

    • Hi Xan. The walrus might get some whiskers, and I do hope the gesso will roughen up the texture on the pieces, as well – I actually prefer a more “organic” look, but I worried about getting too creative with the clay because it could make it more difficult to make the molds. I thought I’d try to do one or two of these critters, or perhaps a full head or two, each day for a while. Maybe after I’ve done a few dozen I might loosen up a little and put a bit more character in the pieces. And by then I should be more comfortable with the process of creating the molds, too. (Messy stuff, that rubber…)

  16. I made my first recipe about two weeks ago. I followed the one in the book, and it was wetter or stickier than I would have preferred. I then saw the YouTube video, and in that, you used two rolls of the toilet paper (I bought the brand you recommended) and the other ingredient measurements of glue and joint compound were a little different. I was wondering which recipe you use the most for regular sculpting? I don’t want to add any flour – lots of humidity and lots of buggies in my area of the country, so just in case……And, I didn’t put in the linseed oil – couldn’t get the darn top off of the container! Good grief! I recall that you said neither one would be essential to the clay.

    • Hi Ginny. I use the recipe that’s currently on the paper mache clay page, but I don’t always use the same brand of toilet paper. When I switch (to get cheaper prices, I measure the paper the first time I use it. I think the paper I used for my first video was a smaller roll, so I needed two of them. I’m using about 1 1/2 cups of wet paper pulp (most of the water squeezed out), although I think you could add more if you want. The recipe still works if you play with it a little.

      The flour does help create the consistency you want, but if you have humidity problems and you want a stiffer clay, you can replace the flour with powdered marble (also called chalk or calcium carbonate). You need to go lightly on the calcium at first because it seems to soak up water a bit slower than flour, so you could end up with a clay that’s stiffer than you like. Just add a bit, mix, let it sit for a few minutes, and check the consistency. I bought my powdered marble online, but I’ve been told that you can get it much cheaper from a sporting good store, where they sell chalk for making lines on baseball and football fields.

  17. I also have a question about the consistency of the clay. I made a batch two days ago, using regular joint compound, but it had separated into a layer of water on the top. I thought I had mixed it well, and I thought I had squeezed all the water out of my TP, but the clay is VERY soft, really too soft to sculpt.
    How much flour can I get away with adding before it distorts the clay? Thanks for your help!!!
    Ann

    • Hi Ann. This is an interesting question, because I’ve never encountered anything like it. Did you measure the amount of paper in your TP roll after you squished out the water? I can imagine the clay being too wet if there was not enough paper. Did you use Elmer’s Glue-All brand glue, or another brand that might not mix in as well? And did you use the pre-mixed joint compound that comes in a plastic tub? The clay will never be the consistency of oil-based or water modeling clays, but you should be able to spread it with a knife and form intricate details when the clay is layered over an armature. Has anyone else encountered this problem? Any suggestions?

  18. Perhaps an idea for finishing the pieces would be to make a plaque with a bit of background details where each animal would live… Then mount the head into it’s habitat~~~ although to be completely objective, the walrus might not work as well that way as the others because of the bleak environment they live in… Just something in addition to the plain background to keep it from looking like a trophy.

    It sounded like a good idea at the time!
    Ann

    • Interesting idea. Or perhaps it would be fun to use some simple line art incised into the plaque, perhaps based on ancient rock art or carvings from the animals’ habitat. Hmmm. I wonder how that would work with the walrus tusks hanging below the plaque – I think I need to get out my pencil and play with it a bit. Thanks for the tip – and I hope we get your clay problem figured out, too.

  19. These are great, very cool. And I’ll have to check out the smooth-on product. I had a bad rubber mold experience a bunch of years ago and now just make them from straight plaster … but perhaps it’s time to look again. : )

    I’ve tweaked the recipe in a couple of ways, but probably most relevant for you is the very first time I made the clay. I thought I was following your directions but I used dry joint compound powder (regular set, sheetrock brand) because I assumed that’s what you were using. I also clearly left too much water in my toilet paper so needed to add more dry ingredients. I ended up adding more flour, more joint compound powder, also some chalk and volcanic ash (because I had it, and what the hell …) and ultimately getting to a fairly wet clay consistency. (I was thinking I’d be able to roll it out like water-based clay, but it wouldn’t roll easily) … I pressed about 1/4 inch into a plaster face mold (with a glad wrap as a separator), and made a couple of square tiles and round balls and cubes in different sizes. (I was looking for drying time, distortion.)

    When they were dry, I discovered the pieces were incredibly strong. I could throw the pieces on the floor and they would bounce. I could stand on one (one curled because I messed with it while it was drying) … and it didn’t break. They felt more like plastic than paper or plaster, and were fairly smooth. They did take a bit longer to dry, but it was my first try so I didn’t know what to expect in terms of drying time.

    Have you tried powdered joint compound instead of plaster?

    • Interesting… I do know now, after the pieces have had time to dry a bit, that the plaster/glue/cornstarch/paper/linseed oil mix did come out very strong, as well. I have a large bag of it, left over from a previous project, so I’ll keep using it for a while. (I don’t have any volcanic ash, though.) I’ll try the dry joint compound, too, now that you’ve mentioned it, but I’m happy so far with the way the pieces are turning out. Next, I’ll try to figure out how to use the mix in a two-part mold with areas that I wouldn’t be able to reach with a brush. That’s something I’ll work on next week, perhaps. Any ideas?

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