How to Make a Rubber Urethane Mold for Casting Starfish

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Here's my tutorial how to make a rubber urethane mold for Casting Your Very Own White Finger Starfish.

starfish rubber urethane mold
Now, why would I want to cast starfish when I can buy real starfish for as little as a buck a piece (or even less)? Well, the fact that these pretty animals are harvested alive for decor purposes just makes me cringe, therefor I don't buy starfish (nor shells or any other sea life). If you feel the same, you'll love this project!

urethane mold rubber
What you'll need is Urethane Mold Rubber (comes in two parts) and Mold Release Spray. I ordered everything from ill Street Composites.

how to make a rubber mold
Then you'll need a flat frame or box. Husb made up this simple wood frame. I have three finger starfish that I received as a gift (see Sparkling Glitter Crafts). One of the starfish was a perfect model! Flat and nicely shaped. Oh, and if you can figure out how to make a frame that's starfish shaped, do so! Turned out the square rubber mold was a bit stiff which made it hard to release the cast starfish, so I ended up cutting away lots of material. Why waste rubber mold if you don't have to, right.

make a rubber mold
Apply plenty of silicon sealer around all the starfish fingers so the rubber urethane mold will not undercut. Try to align with the outermost edge of the starfish, then it will be easy to release the cast starfish. I wish I had done a better job with this!! And as seen in the previous picture, coat everything with mold release spray. Be very generous!

how to make a urethane mold
Then, mix the two parts of rubber urethane mold together and pour until starfish is covered. Let dry over night.

mold making
Release time! Disassemble your frame.

how to make mold
And lift off the rubber mold.

starfish mold

rubber starfish mold
And after cutting away all the extra material, I have a perfect rubber urethane mold to cast as many starfsh as I wish! I'll show you how to cast awesome and real looking Faux plaster starfish next week. So stay tuned!

Update: Becca's question (see comment):
How much did the supplies cost to make the mold?
Mold material $24 and release spray $9. If you plan to cast many starfish, it's well worth it! And the plaster is really inexpensive -coming up next week!

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Becca @ The Sassy Penguin said...

Super cute idea. On average though, how much did the supplies cost to make the mold?

So many ideas running through my mind for uses of starfishies!

Maya @ Completely Coastal said...

Becca, I added the answer at the end of the post. Thanks for stopping by!!

Jane said...

Interesting idea...and I see so many other possibilities with this. Thanks for sharing, Maya.

One question...did the bumpy characteristics of the sea star transfer to the mold?

Sherri said...

Maya, that is really cool! I love it!

Maya @ Completely Coastal said...

Jane, yes it did! I will post pictures of cast starfish next week. So check back in then. Okay.

Pink Overalls @DIY Home Staging said...

This is my kind of project! Can't wait to see how your castings turn out and how you will use them. Thanks for doing our homework for us.

Ideezine said...

All is well when the creative ideas soar. This is a great one.

Kateo said...

I am grateful for this tutorial and even more grateful for your message about harvesting the creatures of the sea for craft/art purposes. There is a reason that within many state beach parks and our National Seashores, you are asked to leave the remnants of sea life (shells) in place, as they return minerals and nutrients to the environment.


Sheer Serendipity said...

I love this project, I can think of so many other things that can be made with this method. Have a great weekend!

Unknown said...

Hi Maya,
I really like the idea of making my own starfish. I went to the website and they didn't have the "75-60 RTV".
Any ideas of where to look next? Also, what kind of silicon sealer did you use?

Maya @ Completely Coastal said...

Erin, I would check art supply stores! Regarding silicon sealer, we used window silicon sealer from Home Depot. Hope this helps!!

Diane said...

Thank you for posting this wonderful idea! I, too, cringe when I see dried starfish, seahorse, or any once living being used as decor. I have been trying to find a way to create faux starfish and I cant wait to try it!

'Go With The Faux!'


Laura Haines said...

Could you not trim the excess rubber and use the mold that way? Thanks, Laura

Maya Nagel said...

I tried that, but if you don't trim the excess rubber then the mold is not very flexible which makes it really hard to release the starfish. Maybe if you used the Hydrocal Casting Plaster (reinforced with fiber), you might be able to get it out of the mold without breaking. Hope this helps. Thanks for stopping by!

Maya @ Completely Coastal

JoAnne Speers said...

Great post; thanks so much. I successfully tried this and saved molding material/urethane by using "Plastina" clay to fill in the spaces among the starfishes' arms. I also used it to keep the urethane from running under the starfish "models," since mine weren't flat. I posted a picture on my Pinterest board of the mold-making process.

Maya Nagel said...

JoAnne can you add the link to your pinterest board! I'd love to check it out!!

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