Why Plaster of Paris Casting?
Plaster of Paris has many advantages over other casting materials. We, at ComposiMold have been using Plaster of Paris to create great theater backdrops, toys, and other crafts. Here’s a list of possible reasons why you may want to use ComposiMold’s Plaster of Paris.
- Is it because Plaster of Paris is a low cost casting material? So true. At $1.94/pound
for the 35 pounds of ComposiMold Plaster, there are not many lower cost options.
And at that cost, you can use it for all your casting projects.
ComposiMold Plaster (NOW LOWER PRICE) is strong and hard when cured. If you want a material that can work outdoors,
we recommend Composi-Stone, an even stronger casting material.
- And what about the molding material? Wouldn’t you want a mold making material that is so low cost that you won’t have to buy any more? How about a reusable mold making material that lets you make hundreds of unique molds just by melting and re-melting. And it works very well with ComposiMold’s Plaster of Paris.
- Do you want to use Plaster of Paris because it’s easy to cast with ? Yes, very true. Just add water, mix, and pour into your ComposiMold mold.
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Why ComposiMold’s Plaster? ComposiMold Plaster Additive is specially formulated for strong, hard castings that cure fast. Working time of 15 minutes, demold in 1 hour, complete cure in 24 to 48 hours.
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If you are using regular Plaster of Paris, use ComposiMold Plaster Additive to make stronger castings that cure hard in ComposiMold molds. Regular plaster can leave dull/weak areas on the surface. The additive eliminates the soft skin from occurring in ComposiMold molds.
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You can start with
- ComposiMold Plaster Additive
- ComposiMold-Original
- Bubble Buster
- Mold Release (just use vegetable oil)
Do you want to make metal castings using plaster molds and the lost wax process? How do you make a plaster mold for metal castings? This is the lost wax method. Use ComposiMold or ImPRESSive Putty to make your mold for your wax casting. Then use the wax to make a plaster casting. Then melt/burn out the wax to give your wax casting. Ideally you want to suck the metal into the plaster casting to fill the mold cavity. Here’s a video showing a home process. The high temperatures can be dangerous, so use caution and seek professional help.
Here's another Application! Use Plaster of Paris for Fillers in Resin Castings . Reduce the amount of resin you use in your castings by using plaster as a filler. With ComposiCast resins, you can add up to 50% by volume to your resin and still get excellent casting. This reduces your costs and reduces the heat created during the resin cure.
What do you need for Plaster of Paris Castings?
ComposiMold Plaster or ComposiMold Plaster Additive If you’re convinced that another plaster is better or maybe less expensive, then we highly recommend at least using the ComposiMold Plaster Additive to make the plaster stronger. Add 3% by weight of the plaster additive to make any plaster work better. The ComposiMold Plaster Additive will work with Plaster of Paris, Ultracal, Hydrocal, and other plasters.
Where did the ComposiMold Plaster Additive come from?
Many people were having difficulty making plaster castings in ComposiMold because the surface was drying out in the ComposiMold. We needed a solution that would reduce the moisture from being absorbed by the ComposiMold. Stan and Shawn developed a material that could harden the plaster faster and from the outside first. This stopped the moisture from leaving and also created a stronger and harder overall plaster. The final ComposiMold Plaster product is better and stronger than the plaster of paris.
Why Would you NOT want to use Plaster for a casting material?
No matter how strong and hard we make it, Plaster is still brittle. Unlike a plastic, plaster will break. It also cannot be used for miniature pieces as well. Don't use plaster if your looking for parts for outdoor use or you want a different feel than plaster can provide. This is where using plaster as a filler can be useful to get the lower cost advantages of plaster with the ductility of resins like epoxy plastic.
Instructions for Plaster of Paris Castings
Casting with Plaster of Paris is low cost and easy to do for basic castings.
For ComposiMold, please use our ComposiMold Plaster that has been formulated to cure to a strong solid casting in these molds. By creating cure more quickly, the water in the plaster does not react with the ComposiMold to give strong, hard plaster castings. You can also purchase a powder additive to add into any Plaster of Paris to obtain a similar strong, hard casting.
Plaster of Paris is a great material to use for basic castings and molds and art projects because it is simple to mix and use. The Plaster of Paris sets in a few minutes, although it takes an hour before it is ready to be removed from the mold. It takes 24-48 hours to fully cure. Using Plaster of Paris is easy, but there are procedures to follow that will make you successful in your plaster castings.
Plaster of Paris is not a plastic. It is a hard white substance made by the addition of water to powdered and partly dehydrated gypsum. It is hard like a cement or concrete but white and not as strong. So don’t use plaster for very thin castings. Basic shapes or designs that have a solid backing to them will be more successful. If you need some flexibility or stiffness in the final castings, then move to a plastic.
The ideal ratio for a Plaster of Paris mixture is 3 parts Plaster of Paris powder to 1 part water. Measure out the water and pour it into your mixing container. Some recipes suggest 2 parts plaster to water, but this will create a much weaker plaster casting. The thicker you can be while still being able to pour the better. Start with a 3 to 1 ratio and if necessary add small amounts of water to make it easier to pour.
- Break any clumps of plaster up with a spoon. If you use your hands to mix, be sure to wear gloves.
- When mixing the water and plaster, you should mix the powder into the water. Pour the plaster powder into the water spreading it out over the surface of the water. After it is poured all poured in, tap the sides of the mixing container and let the plaster powder fill with water to reduce bubble formation. The plaster powder will sink into the water. When you are finished adding the plaster, it will be slightly above the surface of the water and not easily absorbed by the water.
- Gently stir the plaster and water to form a nice slurry similar to a thick pancake mix. Gentle stirring of the plaster will reduce the chance of bubbles being mixed into the mixture.
- Pour the plaster into your molds. If you want to learn how to make your own molds, check out our mold making videos and get your free mold making e-book.
A couple other tips for casting plaster:
- Do not pour any extra plaster down your drain. It can harden and destroy your plumbing. You can dilute the plaster so it does not create a hard plaster or let it harden and throw it away.
- To make colored plaster, you can add colorants to the plaster mix while it is still in liquid/paste form. Remember that you will be adding color to white, so you will need more colorant to make darker colors. Any types of paint will work.
- To paint the plaster casting after it has cured, use a layer of gesso or primer first to seal the plaster, and then you can paint the plaster any way you want.
Video of Plaster Casting of a Duck Decoy
Mix plaster and water together to a toothpaste-like consistency. Traditional plasters cure well but leave a slight soft layer on the outside of the casting. To avoid this, apply a layer of ComposiMold's Plaster Release to the mold before pouring casts. Fast curing masonry cements work great and cure extremely strong. Follow instructions for mixing ratios. We also have the ComposiStone specifically for this use: strong, smooth castings.
We also have ComposiStone Hard Plaster which works well for hard, strong plaster castings. ComposiStone is harder than plaster, but smoother than cement. It can be painted with most paints.
Video of Casting Plaster of Paris in ComposiMold Molds
Plaster Casting of a Doll Head (Or Creepy Halloween Ornament)
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Use as little water as possible that still allows you to pour or scoop the plaster into the mold. Lower water means a stronger cast. The ideal ratio is 72% plaster to 28% water.
Before and after you use your mold, wipe it with vegetable oil or mineral oil (baby oil) to keep the mold soft and pliable.
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So how do you make a little extra money in your retirement years? You can do what this couple did, make plaster casting signs. “Thank you ComposiMold. We can make different signs anytime we want, just by remelting and reusing.”
“ComposiMold Plaster was designed to make plaster casting low cost, easy, and work great in ComposiMold molds.” Stan, President and Inventor of ComposiMold and co-inventor (with Shawn) of ComposiMold Plaster, ComposiMold Additive, ComposiStone, and EcoLureMaker.
| Seashell in Plaster of Paris, Use ComposiMold's Plaster of Paris or ComposiMold's Plaster Additive |
Plaster of Paris comes as an easy-to-mix formula that mixes with water and dries to a dense, durable, and smooth and bubble free finish. Plaster of Paris is a great material to use for basic castings and molds and art projects because it is simple to mix and use. The Plaster of Paris sets in a few minutes, although it takes an hour before it is ready to be removed from the mold. It takes 24-48 hours to fully cure. Using Plaster of Paris is easy, but there are procedures to follow that will make you successful in your plaster castings.
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Materials you will need:
Plaster of Paris powder. For ComposiMold or ImPRESSive Putty Molds, please use our ComposiMold Plaster Additivethat has been formulated to cure to a strong solid casting in these molds. By creating cure more quickly, the water in the plaster does not react with the ComposiMold or ImPRESSive Putty to give strong, hard plaster castings. You can also purchase a powder additive to add into any plaster of paris to obtain a similar affect.
Water: Use cold water to cure slower and give you more control over the reaction and give more time to fill the molds.
Mixing container that is large enough to hold to water and plaster. Plastic containers are nice because you can deform them afterwards to break away the hard plaster and re-use the container.
Measuring cup or any cup that can be used to measure out 3 parts of plaster powder to 1 part water.
Make your Plaster Castings
The ideal ratio for a Plaster of Paris mixture is 3 parts Plaster of Paris powder to 1 part water by weight or volume. Measure out the water and pour it into your mixing container. Some recipes suggest 2 parts plaster to water, but this will create a much weaker plaster casting. The thicker you can be while still being able to pour the better. Start with a 3 to 1 ratio and if necessary add small amounts of water to make it easier to pour.
Break any clumps of plaster up with a spoon. If you use your hands to mix, be sure to wear gloves.
When mixing the water and plaster, you should mix the powder into the water. Pour the plaster powder into the water spreading it out over the surface of the water. After it is poured all poured in, tap the sides of the mixing container and let the plaster powder fill with water to reduce bubble formation. The plaster powder will sink into the water. When you are finished adding the plaster, it will be slightly above the surface of the water and not easily absorbed by the water.
Gently stir the plaster and water to form a nice slurry similar to a thick pancake mix. Gentle stirring of the plaster will reduce the chance of bubbles being mixed into the mixture.
Pour the plaster into your molds. If you want to learn how to make your own molds, check out our mold making videos and get your free mold making e-book.
A couple other tips for plaster casting:
Do not pour any extra plaster down your drain. It can harden and destroy your plumbing. You can dilute the plaster so it does not create a hard plaster or let it harden and throw it away.
To make colored plaster, you can add colorants to the plaster mix while it is still in liquid/paste form. Remember that you will be adding color to white, so you will need more colorant to make darker colors. Any types of paint will work.
To paint the plaster casting after it has cured, use a layer of gesso or primer first to seal the plaster, and then you can paint the plaster any way you want.
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