I tried using plaster of paris, but my object won't release!?

Question

I have been trying to use plaster of paris to make a mold of a simple object. For a test, I used a small wooden wheel. Its solid with no undercuts, holes in the middle, or anything like that. I rubbed vaseline all over it as a release. Well, it was vaseline for babies, but i think thats the same. I rubbed lots on there but smoothed it down and got it smoothed down in the ridges on the wheel so it would get the detail.

I had rubbed the plastic holding container with this vaseline as well. I checked it about and hour or two after it had become hard. The large block of plaster was able to come right out of the holding container with no problems. The wheel looks like it is permanently a part of the block though. I havent tried to remove it yet because it hasnt been 24 hours, but it doesnt look like its gonna budge at all.

Did i do something wrong? Is wood not a good thing to use?

Answer 1

It sounds like you did everything right. You could try giving the wooden wheel a gentle tap with a hammer from the side and see if that makes it move. (I am assuming you are making a 2 part mold and have problems getting it out of one part). If the wood is very rough I could see problems, and if water will soak into the wheel it could make the wood swell, but the vaseline should prevent that.

One thing which could have happened is that while you didn't have an undercut you had no draft either. If you would make a mold of a cube, you would have some problems getting it out as it doesn't have any draft, despite it doesn't have an actual undercut. And sometimes you have a undercut which is so slight, that you don't realize it's one. See if you can get it out some way (hammer or s******g a kind of handle into the wood to give you more leverage at pulling. Sometimes things get stuck a bit, but can still be removed with some encouragement without breaking the mold. Then check your mold if you can figure out what was wrong.