Suppose I have a detective pikachu mold tray, some hot glue sticks and a small cooking pan.

Can I melt the hot glue sticks in the small cooking pan and use it as a resin, to be pour into the detective pikachu mold tray?

Will it cause any damages to the cooking pan, or the mold tray?

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    Why don't you use the glue gun to apply the melted glue sticks directly to the mold tray? Using a cooking pan will lead to random results, as you will not be able to control the temperature properly. – virolino May 27 at 5:45
  • @virolino, actually the main objective is to turn hot glue as resin, but it seems like it can't work, as described in the answer below. – user275517 May 27 at 9:28
  • So at least I was right about one thing: the temperature control of melting can be a (serious) problem. – virolino May 27 at 9:42

It won't work.

You can melt hot glue in a pan, but it tends to turn yellow and eventually brown if it gets too hot. whether the mold survives the pouring depends on the material.

The real problem is that hot glue shrinks quite a lot while cooling down. The mold surface is cooler than the hot glue, so it sets at the outside first, while the center stays liquid for longer. As the center cools down and shrinks, it pulls all surface areas towards the center, warbing the object and possibly damaging the mold.

I've done this experience with a very small object: a papercut of a treasure chest, no more than 2 x 1 x 1 cm. I wanted to add weight to the object and filled the whole thing with hot glue. Once it was cool, the side walls were notably pulled in and there was a big (relatively speaking) hole at the top of the hot glue, where the top surface was pulled towards the center.

  • Good to know that melted hot glue cannot be used as resin. Thanks. – user275517 May 27 at 9:23
  • If this answer helped you, please consider accepting it as described in the tour. – Elmy May 27 at 9:30
  • I wonder (mostly curiosity): will the result change a lot if the mold was "hot" from the beginning, and the mold+glue would then coll gradually together in a closed chamber with "controlled" temperature? Maybe use the chamber to heat the glue directly in the mold? – virolino May 27 at 9:43
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    @virolino I doubt it would work. The temperature difference between hard and molten hot glue is very small, so controlling the temperature in the chamber needs to be extremely precise. And that doesn't change the fact that the cast would ultimately shrink smaller than the mold. – Elmy May 27 at 11:12
  • Aha. Thank you for the information. – virolino May 27 at 11:18

One way it might work is to mix as little hot glue as possible with as much as possible of something with a lower coefficient of thermal expansion. Sand for example. This will also make it stronger. Hot glue isn't generally a decorative finish but if you're using one that is you might want to melt your glue, coat the inside of the mould, then add your filler. Certainly this would be effective in the case mentioned in @Elmy's answer (adding weight).

Melting in the oven might be better than on a stove as you can control the temperature (including testing a small batch). Some hot glues would actually melt in a pot immersed in boiling water but most need a higher temperature than that. 120°C would be a good place to start. I suggest using a dedicated container such as a clean food tin (or even a glass jar in the oven) as normal hot glue isn't intended for food use, and isn't easy to get rid of completely.

  • The first paragraph was going to be a comment on Elmy's answer. Then it grew. – Chris H May 27 at 12:22
  • @user275517 I just got the idea that a different material would probably be better suited for casting. Candle wax is cheap and easy to melt and I think it doesn't shrink as much as hot glue. Soap is another alternative with a similar melting temperature to hot glue. Both come in different colors, so you can give the cast an artistic touch. – Elmy May 28 at 6:09
  • @Elmy paraffin wax has a rather large CTE (at least as much as EVA which is common in hot glue), but beeswax would work. Crystallisation is important - it's quite an interesting topic (IMO, but physics is what I do) – Chris H May 28 at 8:52
  • @ChrisH, if the supplier did not state what type of wax, can I assume that the candle wax is actually paraffin wax? – user275517 May 30 at 1:05
  • @user275517 I would. There are other possibilities but I think its the cheapest – Chris H May 30 at 5:33

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