Advanced Casting Instructions


Advanced casting

Casting using
dental stone

Casting using
plastic & resin

Customer reviews
of US products

Customer reviews of
overseas products

How to mix just enough plaster for one mold.
Using the "wet water" method for better castings.
How to set up your work area for casting multiple molds.
Making a vibrating table for about $40.
How to use a surfactant.

How to mix just enough plaster for one mold.
1. Start with two 9 ounce plastic cups. Fill one of the cups with about 1/2" of water. You can find these at Wal-mart very cheap.

Nest the cup with water inside of the empty cup.

2. Draw a line on the outside cup at water level. Remove the inner cup (with the water), mix up and pour your plaster into the mold.

It looks like I could have used more plaster. Be sure to scrape the mold.

3. After the plaster sets in the cup, flex the cup and the plaster will crack away leaving a clean cup.

We'll use the cup again by placing it back inside the cup with the line.

4. Since we needed more plaster the next time, place a new mark on the outside cup a little higher. Never use the outside cup to mix plaster in. Only use it to measure by placing other cups inside of it. After a few casts, you'll be able to get the mixture very close to filling the mold without much waste.

Using the "wet water" method for better castings.
1. One reason plaster won't flow into the mold is because of surface tension. By using an additive that breaks the surface tension, you can make the water "wetter", allowing it to spread and flow easier.

"Wet" water can be made by adding a little rinse agent. My favorite is "Jet Dry". You add it to your dishwasher to keep your dishes from getting spots.

You'll notice the drop of wet water on the right spreads out more than the drop of plain water on the left.

2. Get plastic container large enough to fit a mold in. Put an inch of water in it and then a very small squirt of "Jet Dry". Gently mix it into the water so you don't cause a lot of bubbles.

If you have several molds you can use a small bucket instead. This will allow you to dunk and leave several molds submerged in the "wet water" solution at one time.

3. Submerge the mold in the "wet water". When dunking a mold for the first time, look closely and you will see several air bubbles caught in the details on the mold. These air bubbles need to be removed in order to get a good cast.

Please note that you only have to remove these air bubbles once. Once the "wet water" solution reaches all of the crevices on the mold, it will continue to flow there again each time you dunk it. From then on, plaster will easily flow into these details.

4. You can remove the air bubbles with your finger, or in small tight areas use a dull pencil or cotton swab.

If you use a cotton swab, try to find the kind with the wooden stick. The paper ones dissolve rather quickly.

5. Remember, you only have to remove the air bubbles before your first cast. After that you simply dunk the mold before casting and don't worry about removing them.

Smack the excess water out of the mold. To do this, hold the mold in one hand and smack it face-down into your other hand. It won't be as messy if you do this over a trash can or towel.

Fill the mold as usual while tapping on the work surface.

6. You'll notice that the plaster will flow everywhere, even off the top of the mold, making more of a mess than usual. Be sure to pound on the work surface as you're filling the mold to bring air bubbles to the surface.

When you need to fill a lot of molds, place a half gallon of water in a bucket and add 3 tablespoons of Jet Dry to it. Dunk the molds in the solution and shake off the excess before filling with plaster.

How to set up your work area for casting multiple molds.
1. Here's a way to set up for multiple mold casting. Start by laying out or taping down a large trash bag down to protect the work surface.

The "pound board" is a small board with pieces of kitchen sponge taped to the bottom. We'll pound on this board to remove air bubbles.

The "trash tub" is an 18 gallon tub I picked up at wal-mart. It's handy because it's wide and short. If you can't find a tub, a wide low cardboard box with a trash bag inside will do.

The bucket of wet water (as mentioned above) contains about 1/2 gallon of water plus 3 tablespoons of "Jet Dry" rinse agent. You can also use dishwashing detergent instead.

Be sure to protect your clothing by wearing an apron or old clothes that you don't mind getting plaster on. For the best casting material (in my opinion), visit our Dental Stone page.

2. Dunk your molds into the bucket and leave them there until you need them. Don't leave them in the solution over night! I did by accident and the mold had a strange residue on it (it rubbed off but still had me worried).

Place a small plastic cup in your casting material box. You'll use this to scoop out and sprinkle the powder when you mix it.

3. Take a 16 ounce plastic cup and fill it a little less than half full.

Sprinkle in your casting material until you get lumps on the top surface that have soaked up the water. When you don't have any water standing on the surface, and all of the particles are wet, then you've added the right amount of plaster.

4. Stir the plaster well. It should be the consistency of a thin milk shake or pancake batter.

Remove one of the molds from the "wet water" bucket and shake off the excess water. In fact, smack the mold face-down on the table to remove the excess water. If there are any soap bubbles in the mold, they will keep plaster from flowing where it should!

5. Pour directly from the cup. Pound lightly on the board as you fill the pockets of the mold.

You will fill about 4 molds before you run out of plaster.

6. After you complete your first four, wipe off the spoon and pound board.

Start mixing up your next batch of plaster while the first four molds are setting up.

7. As soon as you've completely poured your second set of 4 molds, then it's time to scrape the first four.

Place a paper towel over the tops of the molds. You don't have to do this, but it just makes scraping much neater. You also need a paper towel to clean off your scraper anyway, so I use the same paper towels to do both jobs.

8. Scrape the excess plaster off with a 4" wide putty knife. At this point, the plaster should be the consistency of toothpaste.

Clean off the scraper using the paper towel from the mold. Let the excess plaster flow off the side and onto the trash bag surface. When the plaster cures, the excess will easy to remove.

9. After the first set of molds are scraped, mix up and pour your third batch of molds.

When finished, it's time to soak off and scrape the second set of molds. You would continue this process until you run out of molds or space to place them on the table.

10. When you've finished filling and scraping all of the molds, let them set for at least 25 minutes.

Remove the blocks over your trash can so the excess scraps will fall in. I'm placing my pieces into a dehydrator rack so they will dry quickly.

If there is any plaster residue on the mold surface, simply rub the palm of your hand on the mold to remove it. These molds don't need any special preparation or cleaning between casts.

11. There are other methods that my customers will use to cast the blocks so don't feel that this way is the only way you can do it. Many customers use the glass method (placing a piece of glass over the top of the mold instead of scraping it).

In my experience you get a much more exact block height if you wait until the plaster is of a toothpaste consistency and then scrape all the molds uniformly.

Making a Vibrating Table for about $40.00
1. A vibrating table will reduce the number of bubbles in your castings dramatically. Dentists have used vibrating tables for years to get perfect casts when making dentures and crowns. Even chocolate makers use vibrating tables for casting chocolate in molds.

The vibrating table shown here made by Handler Manufacturing costs around $185 (priced January 2014) and is large enough to hold one mold. If you really want one of these, you can call Kevin Smith at Kingwood Industrial Products at (908) 852-8655 (he's a Handler distributor) or check on the internet for a dental vibrating table.

2. That's a little too expensive for me, so I'm going to show you how to make a good vibrating table for about $40.

The most important part of the table is the vibrating device. The best I have found (for a reasonable price) is made by Homedics Inc.. It cost me $28.76 at Wal-Mart in the health and beauty aids section.

If you cannot find this type and want to try other brands of vibrating massagers, you may have to change the way you mount it to the board depending on its shape. I have tried using power tools for the vibration (such as an orbital sander), but they were far too noisy, difficult to mount and vibrated too wildly.

List of supplies needed:
  1. A piece of laminated shelf at least 14" x 12". You can buy the shortest 12" wide shelf you can find for about $5.00 at most lumber yards and they can cut it down for you. Any piece of wood will do, but the lamination makes it easier to clean.

  2. Seat cushion foam. The type I have is 2" thick and called Nu-foam. It cost me $4.77 at Wal-mart in the fabrics department.

  3. Mat board that measures about 6" x 12". You can also use thick card stock from a cereal box or thin card board.

  4. Hose clamps. The largest (on the left) is a 3" dryer vent clamp and the smaller is a 1 1/2" hose clamp (which means it would go around a 1 1/2" OD diameter pipe). You can get both of these at any hardware store. These will cost about $2.50 total.

  5. Two sheet metal screws. I'm using size #6 and they are 1/2" long.

  6. Finally is the vibrating massager shown in detail above which cost me $28.76. If you choose a different type of massager, then you may have to find a different way to mount it.
List of tools needed:
  1. A hammer.
  2. A large nail.
  3. A large flat blade screwdriver.
  4. A medium Philips screwdriver.
  5. A couple of 2" C-clamps.
  6. A large pair of scissors.
  7. A tape measure.
  8. A permanent marker.
  9. Elmer's wood glue or Aleen's tacky glue. Pretty much any type of glue will work here.
5. Use a screwdriver to loosen the hose clamps and unroll them all the way.

On the short hose clamp, measure back 2" from the plain end and put a mark.

On the long hose clamp, measure back 5" from the plain end and put a mark.

6. Get the tape measure and a marker and draw the black lines on the board as shown.

The intersection of the lines is where we are going to screw the hose clamps into the wood.

The photo on the right shows what the board will look like once the hose clamps are screwed in.

7. You won't be able to put a screw through the hose clamp unless you drive the nail through the hose clamp into the board (not all the way). This will spread the slot in the hose clamp out enough so you can get a screw through it.

Now screw a #6 machine screw through the hose clamp and into the board and tighten it down completely.

Do this for both hose clamps.

8. Now that the hose clamps are secured to the board, place the vibrating massager into the hose clamps and tighten them up around it.

The first photo shows the small hose clamp closing around the small end of the vibrator.

The second photo shows the large hose clamp put around the large head of the vibrator. Do not tighten this down too tightly or the vibrator may not work.

Update as of 4/23/06

After using the vibrating table for several months, I've noticed that both hose clamps will break.

The hose clamps break because they make a sharp bend right under the screw heads. The vibration causes too much pressure on the thin edges of the hose clamp and it will snap after continued use. I even tried adding a rubber washer under the screw heads, but the clamps continued to break.

To solve this, I decided to replace the hose clamps with nylon straps. The kind shown here cost about $1.99 and come with a plastic buckle. I used the same #6 sheet metal screw and added a #6 steel washer under it. Otherwise the head of the screw would pull through the strap.

Be sure to put the screw close to the buckle, especially on the small end of the handle. Wrap the straps around the vibrator and pull them as tight as you can. Use scissors to cut off the extra strap.

When finished, the vibrating table will look like this. You won't have the option to tighten and loosen the large belt to adjust vibration, but so far that hasn't been a problem.

Because I can't tighten this kind of belt as tightly (just pulling on it by hand), the vibrator moves around on the table a little and is a little noisier because the pads are hitting the board, but it does an excellent job of getting rid of air bubbles in your casts.

9. Lay the table on top of the piece of cushion foam and draw around it. Use the pair of scissors to cut the foam a slight bit smaller than the size of the table.

If you have difficulty cutting the foam with scissors, you can also make several cuts with a hobby knife.

10. Glue the table on top of the foam using the wood glue.

Finally, take the piece of mat board (or card board) and glue it to the bottom of the foam, making sure that it sticks out about 1".

The mat board will be used to help clamp the vibrating table to your work surface when you cast.

11. Use the C-clamps to hold the table in place.

You can adjust the vibration by using the slider adjustment on the massager, or you can also loosen or tighten the large hose clamp.

12. When mixing up plaster, touch your cup to the vibrating table to remove air bubbles in the mixed plaster.

When pouring plaster into the mold, steady the mold with one hand and pour the plaster with the other.

You will have the best results if you use the "wet water" method along with this table. Using the vibrating table will allow you to mix plaster slightly thicker than normal and still get good casts.

How to use a Surfactant
A surfactant is a wetting agent. It's a chemical agent capable of reducing the surface tension of a liquid in which it is dissolved. This is pretty much what wet water is, which is shown further up on this page.

However, the product I'm reviewing here works a little better than wet water made from a dishwasher rinse agent. I found this product at Pacific Dental Supply and a direct link to the product from their online shopping cart can be found here.

At the writing of this article, an 8 ounce bottle costs $11.50 plus shipping. It may seem expensive but this 8 ounce bottle will get you through a 50 pound box of dental stone. The photo on their shopping cart does not show the spray top but they send it along with the bottle. It's a high quality spray nozzle that puts out a fine mist.

If you run out of the liquid, you can always mix up your own wet water and spray it from the bottle, which works fairly well because of the high quality of the spray nozzle. I thought the spray pump was worth the price alone because of how well it works.

This stuff is pretty easy to use. Just hold the bottle about 6" away from the mold and give it a good even coat on the surface of the mold.

This usually takes from 6 to 8 squirts from the bottle to get the whole surface. Flat floor tile molds take a little less and deep molds take a little more.

Immediately after spraying, pour your casting material into the mold and vibrate it or pound on the mold table as usual. You will see the casting material slide around and creep into all the cracks of the mold.

Sometimes when mixing up your plaster (especially the dark gray Merlin's), you can end up with micro bubbles on the top of the cup - lots of tiny bubbles that do not seem to pop. If you spray the surface of the cup with this stuff, the bubbles break instantly.

I have a sneaking suspicion the colorant is part of the micro bubble problem (though I have no facts to back this idea) because this product causes the colorant to break up on the surface of the plaster as well.

At one point I ran out of the surfactant. Instead I put a tablespoon of Jet Dry rinse agent in the bottle and filled the rest up with water. This worked fairly well and got rid of most of the bubbles in the mold. It still did not seem to do quite as well as the actual product - but it was very close. However, spraying this mixture onto the plaster did not break micro bubbles on the surface.

If you live overseas and cannot get this product, I'm pretty sure that most other brands of "surfactant" would do well also. If nothing else, you could mix up some wet water and spray it on the molds instead. If you do this, be sure to get a high quality spray bottle. Get one that produces a very fine mist such as found in hair care products.

In conclusion I would say that this product is well worth the money. I certainly don't miss the days where I had to dunk the molds (and my hands) in a bucket of wet water to get rid of bubbles.

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