My question is this: will I need to bake the plaster mold in an oven to remove moisture after I've taken the master out? Is this a necessary step? Could I let the mold dry out for a few days instead?
Thanks in advance for the assist
Making a Plaster Mold
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Making a Plaster Mold
I'm thinking of using plaster instead of rubber for a mold. The pattern that I'm using is pretty smooth (no greeblies or detail) so I think that plaster will work.
My question is this: will I need to bake the plaster mold in an oven to remove moisture after I've taken the master out? Is this a necessary step? Could I let the mold dry out for a few days instead?
Thanks in advance for the assist
My question is this: will I need to bake the plaster mold in an oven to remove moisture after I've taken the master out? Is this a necessary step? Could I let the mold dry out for a few days instead?
Thanks in advance for the assist
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Scott Hasty
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What are you using to cast into the plaster? If it's any form of resin...you might want to read on...
Unless you are using one of the Ultracals, FORGET plaster. Personally, I would say forget ALL plasters. Ultracal is the best, hardest, lowest shrinking plaster around. I use it in making molds for make-up prosthesis. That being said, you will ALWAYS find trace amounts of water in mixed-and-cured plaster. Water + Resin = A BIG MESS! Besides, for what you'd pay for Ultracal, you could easily buy a quart of silicone.
In this case, I would say use the proper materials or find an alternate method of building it.
Scottie
Unless you are using one of the Ultracals, FORGET plaster. Personally, I would say forget ALL plasters. Ultracal is the best, hardest, lowest shrinking plaster around. I use it in making molds for make-up prosthesis. That being said, you will ALWAYS find trace amounts of water in mixed-and-cured plaster. Water + Resin = A BIG MESS! Besides, for what you'd pay for Ultracal, you could easily buy a quart of silicone.
In this case, I would say use the proper materials or find an alternate method of building it.
Scottie
Last edited by Scott Hasty on Tue Jun 05, 2007 10:56 pm, edited 2 times in total.
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Scott Hasty
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Joseph Osborn
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Baking plaster
Don't bake your plaster in an oven-- it could crack. You want to use gentle heat, about 120-150 degrees F, and air movement to cure the plaster. Depending on the size of your mold, a cardboard box with a little muffin fan and a 100W light bulb may be all you need to get the job done. Alternately, you can put it in the corner of a room and let it sit for a few weeks and it'll dry out on its own.
<i>Fireball Modelworks</i>
What Scott said about the Ultracal.
If you are going to go that route, you can reinforce the mold by embedding strips of burlap into it. When it's set up and dried out, you can seal the cavity with parafin wax (I think, it's been a long time since I did an Ultracal mold) or clear acrylic spray paint (again, it's been a while).
Melt a little wax and rub it in and buff it. If you don't seal it, the resin will never release from it.
HTH
Dennis
If you are going to go that route, you can reinforce the mold by embedding strips of burlap into it. When it's set up and dried out, you can seal the cavity with parafin wax (I think, it's been a long time since I did an Ultracal mold) or clear acrylic spray paint (again, it's been a while).
Melt a little wax and rub it in and buff it. If you don't seal it, the resin will never release from it.
HTH
Dennis
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Scott Hasty
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Yup, parafin is good stuff and makes a good barier to any moisture. But, again, the cost and the PITA factor combined make it more cost efficient to buy a more mainstream product like silicone...DennisH wrote:What Scott said about the Ultracal.
If you are going to go that route, you can reinforce the mold by embedding strips of burlap into it. When it's set up and dried out, you can seal the cavity with parafin wax (I think, it's been a long time since I did an Ultracal mold) or clear acrylic spray paint (again, it's been a while).
Melt a little wax and rub it in and buff it. If you don't seal it, the resin will never release from it.
HTH
Dennis
Let us know what you decide and your outcome! I love to be proven wrong and see success!
Scottie
I am fearful when I see people substituting fear for reason
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Chacal
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When I began using resin, I used to make all my molds in plaster. Things I learned:
Plaster is pretty decent as a mold material, as long as you con't have any undercuts.
Plaster has a grainy surface, no matter if you're molding a glass plate. It will be grainy and not smooth. If you need mirror-like, go with silicone.
You absolutely need to coat the mold with a release agent (I used an acrylic based one, con't remember the name, it was clear, dark green).
The release agent takes care of the moisture problem, as the acrylic layer (acrylic as in acrylic paints, PVA-based) is waterproof after dry.
If you need to make a two-part mold, use vaseline to keep one part from attaching permanently to the other.
You only need burlap/gauze reinforcements if the part is bigger than a foot. If it is smaller, just use a thicker layer.
Wait a couple of days for the plaster to dry before you apply the mold release (the plaster will absorb a bit of the moisture off of it and make a smoother, thinner layer of it).
If you mix the plaster correctly (the right amount of plaster to the water, it gets bone dry in about a day (for about a one-foot sized mold) if you screw up the proportions (either way, too much water OR too much plaster, as paradoxal as it may seem) it'll be moist for a long time, and not too good as a mold.
I used plaster to make molds for clear resin parts to replace the inner warp grilles, main deflector and magnatomic crystal on a 1701-A, ST-V Enterprise and it went without a hitch.
Plaster is pretty decent as a mold material, as long as you con't have any undercuts.
Plaster has a grainy surface, no matter if you're molding a glass plate. It will be grainy and not smooth. If you need mirror-like, go with silicone.
You absolutely need to coat the mold with a release agent (I used an acrylic based one, con't remember the name, it was clear, dark green).
The release agent takes care of the moisture problem, as the acrylic layer (acrylic as in acrylic paints, PVA-based) is waterproof after dry.
If you need to make a two-part mold, use vaseline to keep one part from attaching permanently to the other.
You only need burlap/gauze reinforcements if the part is bigger than a foot. If it is smaller, just use a thicker layer.
Wait a couple of days for the plaster to dry before you apply the mold release (the plaster will absorb a bit of the moisture off of it and make a smoother, thinner layer of it).
If you mix the plaster correctly (the right amount of plaster to the water, it gets bone dry in about a day (for about a one-foot sized mold) if you screw up the proportions (either way, too much water OR too much plaster, as paradoxal as it may seem) it'll be moist for a long time, and not too good as a mold.
I used plaster to make molds for clear resin parts to replace the inner warp grilles, main deflector and magnatomic crystal on a 1701-A, ST-V Enterprise and it went without a hitch.
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