The Secret to a Perfect Hot Glue Mold

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

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!

Comments

[AustinS1]

Hey brother who made the post I have been buying the poly plastic beads they make the best mold I've ever seen and you can melt it down and make another one out of it I'm telling you the detail is amazing it's the best thing going I believe I believe they're called Holly plastic but they are multiple plastic beads used for fake teeth and other things please try it it's super cheap and it's super awesome

[SophieBdoesart]

Sister, but thank you! 😁 As it happens I'm familiar with thermoplastic beads, but I prefer to use them to make positives since they aren't as flexible and can be harder to demold. But they're great for fake horns and vampire teeth. 👍

[GenevraG]

Also, more expensive 👀

[LaraLinx]

Late to the party, but wanted to mention that for those of us looking for a safer/healthier way to create small molds, the wax & hot glue method above uses way less plastic and produces less fumes that might contain VOCs!

[amyhumphries860]

That's very cool and very helpful thank you so much for helping me out when I was stuck🤗..

[SophieBdoesart]

Is that a glue pun? Love it! 😆

[tannishenriksen]

I still dont understand how to put 2 together to make a whole..like a ball for instance. I want to put 2 halves together. Its explained but im not getting it..

[AustinS1]

The way I've done it is I just cast the whole thing and then cut it open so for a ball example just get the whole ball in it for right the whole ball with your mold material then let it dry and then cut it open with a jagged line so you can match it back together using hot glue or silicone you can cut it only partially and just pop it out

[SophieBdoesart]

Hey, sorry I didn't see this sooner! To make a 2-part mold with this the first thing you have to do is follow all the instructions except taking the object out of your half-mold. Instead, coat the part of the mold that will touch the other part in its' own layer of wax. When in doubt, just coat the whole thing, but make sure you’re only using a thin coat.

The next part is slightly trickier and it may help to look at a video explaining how to make a traditional two-part mold, but here goes: You will need 2 thin cylindrical objects. Something like a bamboo skewer would be perfect. Find a place on your object where you can stick them close together and attach the ends with a bit more wax. They don't need to be long, they just need to stick out further than the edge of the mold. The purpose of these is to create 2 channels in the mold. One to release air, (called a "sprue",) and one to pour in your casting material. Coat these in wax too. Then, build your clay walls twice as high as before and fill that with hot glue. You should be able to pull apart the halves quite easily. 👍

[SophieBdoesart]

Remove the skewers before you cast your material. They should pull out pretty easily.

[Imaredhead946]

Thanks for sharing! I found FIVE 4-leaf clovers today and was urgently looking for info on resin and molds because I want to put them inside of a molded "something" while they're still alive (I put them in water).

In the back of my mind I thought about hot glue being an option for making a mold but didn't know enough about resin molding to know for sure if it would work and now I do! 😃 Your mold turned out fantastic! Now I just have to figure out the resin part of everything.

Again, you did a fabulous job! 👍 Thanks for sharing! 😊

[SophieBdoesart]

That is so freaking cool. Just be sure to dehydrate or press them first to get all of the moisture out or they'll decompose inside the resin. If you have any of those "do not eat" dehydration packs from products the silica inside works wonders. If not, you could put them between two tissues in a heavy book for a few weeks or risk the microwave pressing option. 😁👍

[kayemmdee]

Hi. I am new to casting, so have a bit of reading on the topic but zero experience. I liked this idea since I thought it would be a good way for me to get started without investing too much money. I even have a project in mind.

I think I am missing a step -- or need something clarified.

QUESTIONS: After the mold is formed -- presumably in this case the shell is completely encased? How do you get the shell out -- assuming you want your project also to be an identical (3-dimensional) object?

Otherwise, I love this and, once I know how to make it work, want to share it with my granddaughter -- who LOVES arts and crafts!

Thanks in advance for any insights!

[SophieBdoesart]

Great question! This tutorial only covers making the mold of half of a 3D object, but if you want to make a 2-part mold, (a mold for an entire object, with limitations,) you could do the same thing, then cover the entire mold completely in candle wax and cast the other side while the object is still in the mold. If you do this make sure to have 2 small tubes, maybe straws, somewhere in the mold from the object to the outside air. One for air, one for the casting material. You can disregard that if you're casting with clay though.

[WackyPup]

Thanks for posting this! I can't wait to try it!!

[SophieBdoesart]

Anytime! I hope you get some good use out of it. 😁

[spark master]

wonderful!

[SophieBdoesart]

Thank you. 😆

[jackysidd]

Brilliant! Cant wait to try, thank you for sharing. I am wondering if I can use this in school as a different method for the children to make fossils.

[SophieBdoesart]

That would be awesome! Let me know if you do. 😁