Casting instructions

Advanced casting instructions

Casting using dental plaster

Casting using plastic & resin

Customer reviews of US products

Customer reviews of overseas products

There are several kinds of dental plaster so whatever you buy, always look at the compression strength measured in psi (pounds per square inch).

Regular plaster of paris is 5,000 psi compression strength and will chip fairly easily. Hydrocal is around 8,000 psi and is more durable. Merlin's Magic (reviewed below) is around 14,000 psi and is even more durable yet. Excalibur and Die-Keen (also reviewed below) are 18,000 psi and dry so hard it's almost like a ceramic material.

Merlin's Magic comes in white, tan, gray and dark gray. It doesn't matter which color you pick, they all have the same properties. I found that the tan or white colors take stain very well for the wooden plank and wood shingle pieces.

Merlin's Magic cost $39.95 for a 50 pound box and the shipping can cost from $9.00 to $24.00 depending on where you live.

1. Get two disposable plastic cups and nest one inside the other.
2. Pour 2 ounces (60 ml) of water into the top cup and place a black mark on the outside of the bottom cup where the water line is.
3. Place an additional 2.5 ouces of water into the cup (for a total of 4.5 ounces or 135 ml). Then place another black mark on the outer cup at the water line.
4. Remove the inner cup and you you have a reusable measuring cup.
   Here is how you mix the plaster

   

5. Insert a new cup into your measuring cup.
6. Pour in water until it reaches the first line.
7. Carefully shake in the powder until the mixture reaches the second line. The powder must be absorbed into the water before you can determine if the second line is reached.
8. Remove the inner cup, mix up the plaster and pour it into your mold.

Also, the mixing instructions on the package of Merlin's Magic will be different. Their instuctions are used for dental castings, which use a vibrator to shake thicker plaster into their dental molds. If you mix according to their instructions, the plaster may be too thick to pour into a mold.

These two products are almost identical, only the makers of Excalibur have made their product specifically for out hobby, so they're offering is at a cheaper price, cheaper shipping cost, and in the colors of white, tan, gray and dark gray! It doesn't matter which color you pick, they all have the same properties. I found that the tan or white colors take stain very well for the wooden plank and wood shingle pieces.

Excalibur cost $39.50 for a 50 pound box, and the shipping can cost from $9.00 to $24.00 depending on where you live. The Die-Keen was more expensive (from $56 to $74).

You mix this material just like you mix plaster. The Excalibur I'm using is light gray in color (and fairly heavy). Start with a 1/3 cup of water and gently shake (sift) the powder into the water. It will sink quickly. Continue to add the powder until the water won't soak up any more. If all of the powder is wet and there's no layer of water on top, then you've mixed it perfectly.

Gently stir the mixture to remove any lumps. I swear, dentists have the best stuff. The material mixes smoother than any type of plaster I've ever worked with.

Spoon the mixture into each pocket of the mold. Sometimes it helps to pour the blocks 1/2 way, tap the mold sharply to remove air bubbles (I use the handle of my putty knife), then fill them the rest of the way. Even mixed at full strength, this material is thinner than plaster and will flow into the corners easier. Be sure to overfill each pocket.

Let the stuff set in the mold for about 3-6 minutes. Take a putty knife and poke at the edge. If the edge is the consistency of toothpaste, then go onto the next step. This material doesn't act like plaster! As the mixture sets, wet particles continue to sink down into the mold, leaving a layer of water on top. The edges around the blocks will start to set up but the middle of the blocks will still be very liquid.

Lay a paper towel over the mold and let it soak up the excess water that rises to the top. This is why you want to overfill the pockets slightly. If you don't, when you soak it up the excess water your blocks will be short.

Gently scrape across the mold to remove the excess. The mixture will be thin, so you may have to scrape back and forth a few times to level it. The excess won't come off neatly. Let it run off the side of the mold onto your work surface. Once it hardens it will pop right off the work surface easily. Let it set 25-30 minutes before you remove the blocks.

The dental plaster is really strong! I threw a stair section on the floor as hard as I could and it didn't even chip! It also takes glue and paint really well.