The Secret to a Perfect Hot Glue Mold

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About: I'm currently in college studying everything I can. I work in a makerspace where I've really been able to grow a lot. Keep an eye out for new Instructables on the way! Thanks for checking out my page!

I've been making molds for a while now, but I often found myself frustrated by the high costs of materials. I love the quality that silicone molds like Smooth-On give, but I wanted to find a cheaper alternative for small casts. Hot glue was the obvious choice for me because of its price, its flexibility, and its incredibly quick cure time. The one major problem with hot glue is that it sticks to almost everything. I needed to find a mold release that would fill any small pores in the positive, allow the object to de-mold easily, and be as inexpensive and readily available as hot glue to avoid defeating the purpose. I tried everything. Oil, petroleum jelly, even some Smooth-On mold release as a test but none of them worked well enough to not damage the molds when I removed the object. I didn't figure it out until we had a power outage and I was digging through my collection of scented candles. The liquidy, melted wax was perfect for coating objects. Hot glue doesn't stick to it but it goes on thin enough to not obscure the details of the mold. Here's how I finally got the perfect hot-glue mold:

Supplies:

  • Hot glue gun
  • Hot glue sticks, (I used 2.)
  • Oil Based Clay
  • UV cure resin (or any cold-cure material.)
  • Something to cast
  • Candle
  • Old paintbrush
  • Wax paper or other nonstick surface

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Step 1: Building a Well

The first thing you need to do is plug in your glue gun. It will heat up while you make a container for your mold. Using your clay on a bit of wax paper, build up some quick walls. You want the well to be just a little larger than the object you're casting. Don't worry if you don't have any sculpture skills. It doesn't need to be fancy, just functional. Try to make sure the clay is stuck firmly to the wax paper to avoid any leaks.

Step 2: Prepare Your Object.

Light your candle and let it sit for a few seconds until it melts into a clear liquid. Using your old paintbrush, coat your object in a very thin layer of the wax. You need to work quickly as the wax will begin to solidify in a few seconds. If you need to spread it any thinner you can carefully hold your object a few inches over the flames and the wax will liquefy again very quickly. When you're dipping your brush into the wax be very careful not to let the bristles touch the flames. It may help to tilt your candle and let the hot wax collect on the inside of the jar. If your object has a large hole in it like my seashell, fill it up with clay before you coat it in wax.

Step 3: Making the Mold

Fill your well most of the way with hot glue. To avoid any unwanted air bubbles you should keep the tip of the hot glue gun submerged in hot glue the entire time you're filling the well. Make sure you have a few extra glue sticks handy because you may need more than one. When it's filled, quickly push your waxed object into the glue, being careful not to burn yourself. You can wait for the glue to cool naturally but I opted to run it under cold water and it cured in about 5 seconds, allowing me to demold immediately.

Step 4: Casting

You can use any cold cure casting material with this mold, but I opted for UV-Cure resin because I had it on hand. Since cold hot glue doesn't stick to anything you won't need to use any other form of mold release. Simply fill the mold with resin and cure it. I cured it in a UV tank that's meant to cure SLA prints but sticking it in sunlight for a few hours, or under a UV light for 30 minutes works just as well. To demold the print pinch the mold between your fingers and push your thumb against the bottom. The cast will pop out easily.

Step 5: Marvel at the Incredible Detail

The seashell that I found was a test to see how detailed I could get these cheap molds. The result was stunning. My camera can't quite capture the delicate ridges in both the original shell and in the cast version but I'm so excited to take a crack at making 2-part hot glue molds and using this method in future projects. I hope you find this as useful as I do and that this Instructable helps bring down the costs for aspiring mold-makers all over Instructables. If you use this tutorial, please post a picture here. I'd love to see how you use this!

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    39 Discussions

    This is brilliant! And a great idea for those of us new to mold making. Especially since the basic materials are already in our craft stuff!

    What kind of materials can you use in the mold? Air Clay ? Or what kind of resin do you recommend? I have been looking for a way to make a mold from vintage high heel doll shoes. I want to be able to mold the sole and heel.

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    JoopB1

    9 days ago

    Congratulations with first prize! I actually expected that your cool idea would have been the grand prize tho! :)

    1 reply
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    SophieBdoesartJoopB1

    Reply 3 days ago

    Thanks! I'm honestly just super happy I was a finalist. 😂

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    DenniseW1

    Question 12 days ago

    I love this tutorial and I was wondering if this could be done with a fast curing UV resin that takes about a minute or two under a nail lamp? I have been planing on making some gaming dice molds but the molds are way out of my price range along with the mold casting supplies.

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    SophieBdoesartDenniseW1

    Answer 12 days ago

    Thanks! It should work as long as it doesn't exceed 400 degrees. 😁👍

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    Todd_M_Sylvia

    15 days ago

    I like the entire method you created. Will definitely try your process the next time I need to replicate/mold a small item/s.
    Thanks again for your kindness, care, and time putting together an easy to uderstand and obviously very helpful tutorial.(warm smilz)
    Best regards always,

    Todd S. - Monroe, Oregon

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    big_F

    15 days ago on Step 5

    Ok what I want to know is how in all my years making molds, I never thought of this. quite often the small mold ends up costing so much more than the items cast from it ever will, using my standard Silicone and resin methods.

    As discussed here already by another member a hairdryer or hot air gun will help with wax distribution on the Positive.

    Thanks for sharing. gonna add this to my "tools"

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    SophieBdoesartbig_F

    Reply 13 days ago

    Right? I can't believe it took me this long. 😂 Honestly, I just used the heat from the candle flame to distribute the wax. But a hair dryer seems much safer.

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    Iamm1ckser

    15 days ago

    Would making a hot glue mold be suitable to pour molten lead into ?

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    SophieBdoesartIamm1ckser

    Best Answer 15 days ago

    I don't think so. Lead melts about 200 degrees hotter than the glue so the whole thing would probably just catch fire. If you're looking for an inexpensive way to cast lead than you should try the method above but with Plaster of Paris instead of hot glue. It will take a bit longer and it won't be flexible but it's way less likely to burst into flames. 👍

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    lnicoulin3Iamm1ckser

    Answer 15 days ago

    no. the lead would be too hot for the mold. IIRC, you need to use a sand mold for metals. RTV silicone will fail after a single casting and is expensive.

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    BardPIamm1ckser

    Answer 15 days ago

    Molten lead is way too hot, the glue would melt (and possibly burn) instantly.

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    HumbertoB3

    15 days ago

    One complement: if the wax layer gets too thick you can always liquidify it with a hot air gun or hair drier to remove the excess..

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    SophieBdoesartHumbertoB3

    Reply 15 days ago

    Great idea! Be careful of flying flecks of hot wax though. 😉👍