Doh! Plaster trouble.

[ilona]

Ok, the genius here tried to make a plaster mold the other day. I poured the plaster into a bowl and stuck another bowl on top, and put something in there to weigh it down until it dried.

It worked beautifully. The top bowl came out no problem.

However, the plaster is stuck in the bottom bowl now and I am afraid to try too hard to pull it out for fear of breaking the plaster or the glass bowl underneath it. Suggestions?

[Landseer]

What about holding the bowl part under running HOT water to make it expand a little while working at loosening?

[ilona]

I'll give it a shot! You mean to get the glass hot, not the plaster wet...right?

[Landseer]

I'll give it a shot! You mean to get the glass hot, not the plaster wet...right?Yes, it doesnt matter if the set plaster gets WET, but what you want is for the hot water to heat up and expand the BOWL, so the water needs to cascade over the entire bowl. Try that first.

[Merlion]

Just a reminder that unfortunately glass does not expand due to heat.

Showing us a photo can help us understand the problem.

Perhaps slipping more than one pen-knife into the gap and gently easing them apart. Of course avoid places where the plaster mold is thin.

[ilona]

LOL...the plaster is a disaster. Luckily the glass bowl made it through in one piece.

Now...anyone have a suggestion for how to make a nice plaster mold of a large bowl?

:rolleyes:

[fused]

Grease the bowl with vaseline, like you would a cookie sheet with crisco.

[ilona]

AH! Thank you.

[Merlion]

Generally I find vaseline a good separator, in addition to wax.

But why do you said the plaster is a disaster. Can't you join the pieces together again?

[ilona]

LOL - I should take a picture of it to show you. I had to chip the plaster out with a chisel, and it is in thousands of pieces now.

[ilona]

I did it again. Only this time I actually kidded myself into thinking a plastic bag lining the mold would make it easy enough to just pull out after it hardened.

I get the feeling this is an IQ test and I am repeatedly failing.

I think I will post a picture of this one so you can all laugh at me.

[Landseer]

Keep in mind that plaster EXPANDS when it sets, that is #1, #2 keep in mind the slightest indentation, ridge, undercut or even a scratch you can hook a fingernail on is enough to lock plaster in pretty good so it won't remove.

[ahirschman]

You should also remember that most plasters expand (A few plaster types have very low expansion rates, but they still expand a little) when curing. So, you will have a lot of trouble getting them out of tight spots. Does your bowl curve in a little at the top? you may try to add many plastic bags, or some paper towels under the bags to give you a little more room to pull the bowl out once the plaster has expanded. You could also apply a fairly thick layer of Vaseline, or use a cheap metal bowl (The type made out of thin stainless) and cut it in half before (or just cut a line to the middle to allow you to open the bowl a little. Then tape it back and pour your plaster.

[grommet]

Maybe let's back up a bit...
What is it you're doing with the mold when you're done? Are you really going to use that side of the mold that's causing problems? What about half of a ball (basketball size?) set that in the bowl for light support & then set your other bowl inside it?
just some thoughts...

[ilona]

Good idea.

I think it might be sinking in, now, this idea that plaster expands! lol

I am going out of town this weekend, but when I get back I will post a picture of the current dilemma and see if y'all have any suggestions for getting out of it.