Cleaning Clay out of a hydrocal (plaster) mold

[Temperance]

I have a lot of stubborn clay that I can't seem to get out of my hydrocal mold.

Any ideas how to get the clay out?
So far I have scraped and scraped and scraped with various tools... I have tried casting a thin layer of latex in hopes the remaining clay would just peel out with the latex (but no such luck!)

This has never happened to me before.... I used a new clay, which obviously doesn't have the same properties as stuff I have previously used.

I have also heard alcohol or mineral spirits can be used to remove oil based clays, but haven't tried them yet.

Suggestions?

 

[Damocles]

In the past I've sprayed my sculptures with Krylon Crystal Clear before making a mold and the clay always peeled right out. What kind of clay did you use?

 

[Temperance]

Permoplast modelling clay: Permoplast® Modeling Clay - Blue ~ Modeling Clay

I bought it at my local plastics store. Since I get all my hydrocal, resin and latex there, I assumed it would be good stuff to work with.

 

[BornKilr]

In the past I've sprayed my sculptures with Krylon Crystal Clear before making a mold and the clay always peeled right out. What kind of clay did you use?

You definitely need a good coat of clear on the clay before casting. But since thats not an option now, get a hair dryer and heat up the clay. It will turn to liquid and you can wipe most of it out with a paper towel. Use mineral spirits on a brush or Q-tip to get the last bits.

 

[Temperance]

You definitely need a good coat of clear on the clay before casting. But since thats not an option now, get a hair dryer and heat up the clay. It will turn to liquid and you can wipe most of it out with a paper towel. Use mineral spirits on a brush or Q-tip to get the last bits.

Wouldn't the melted clay just absorb into the plaster since it's so porous?

 

[Vermithrax 4]

I've always used acetone and a semi stiff brush to get out any clay remnants out of plaster molds and it's always worked fine for me.

 

[BornKilr]

Wouldn't the melted clay just absorb into the plaster since it's so porous?

You're not melting it to completely liquid, just enough to wipe out. And besides, before you use a hydrocal mold, it needs to be clear coated before using, so any clay residue will be sealed under the clear coat.

 

[Friko]

I've always used acetone and a semi stiff brush to get out any clay remnants out of plaster molds and it's always worked fine for me.

I agree. Just get an old tooth brush and some acetone and scrub it out.

 

[Lancer]

You definitely need a good coat of clear on the clay before casting. But since thats not an option now, get a hair dryer and heat up the clay. It will turn to liquid and you can wipe most of it out with a paper towel. Use mineral spirits on a brush or Q-tip to get the last bits.

pardon my ignorance, but how on earth is hitting clay with a hair dryer gonna melt it? isn't it going to go rock hard?

 

[BatTexan]

pardon my ignorance, but how on earth is hitting clay with a hair dryer gonna melt it? isn't it going to go rock hard?

The description of the clay he's using says it never hardens, so it's likely an oil based clay. If so, it'll get soft and melt under the heat, and that should make it easier to get out.

 

[BornKilr]

The description of the clay he's using says it never hardens, so it's likely an oil based clay. If so, it'll get soft and melt under the heat, and that should make it easier to get out.

Exactly. Yes, I am assuming that it is oil based. I use Plastalina and it melts very easily.

 

[Temperance]

Success! Mold is now clean.

For future reference, you can use a heat gun to soften the oil based clay and wipe out with a cloth.
However! Please note that the extreme heat change can be hard on the mold, if the heat is left too long the mold can crack due to expanding in the heat.

Thanks for the advice everyone.

 

[BornKilr]

Glad it worked. Although I wouldn't have used a heat gun for the reasons you mentioned. It gets much hotter than a hair dryer and the melting temp of clay is pretty low. Most hair dryers on med. heat would probably work fine.

 

[Avarice]

I'm new here and this is my first post. Found the forum upon searching for ways to do my project.

First off I'm trying to make a flat mold for a custom title belt out of plastic. I've seen various +/- on ways to go. I've tried a reusable heated compound for the mold, but it's too hot and melts my oil based Monster Clay.

I'd like to know if I can: 1) use plaster of paris (by Dap) to pour over the clay. 2) If so, can I then pour my part out of plastic into the plaster? Do I need a mold release on the oil based clay for the plaster? Do I need to seal the plaster for the plastic pour and a mold release?

Any help is appreciated. If you want to drop me an email or PM as well, that'd be fine.

Thank You,
Eric