Saturday, April 5, 2014

09 Plaster Production Molds Nº 17

Making a Plaster Build-up [part 2]

Click on any image to enlarge it.

I am going to mix and pour plaster today. First of all, I make sure that I have a lined trash container and a 5-gallon bucket half-filled with water, ready and waiting near my plaster molding table. The trash container will get any extra plaster that is left over after the pour. The bucket of water is for washing off my tools, mixing bowls, and hands.

NEVER put plaster (dry, set, or wet) down the drain pipes.

The tools I will be using to mix and pour the plaster include a scale for weighing the plaster and the water, mixing bowls, a scoop, a sieve, and a yogurt container. I use the yogurt container to bring clean water from the faucet to add to the mixing bowl on the scale.

It is important to use clean, fresh plaster for all production molds. This is a 100 pound bag of U.S.G. White Moulding Plaster. The plaster is kept inside a heavy duty plastic bag to keep it as dry as possible.

I use the scoop to get plaster from the bag, and put it in the sieve. I use a small block of wood to rap the rim of the sieve so the plaster is sifted into a clean mixing bowl.

Before I weigh anything on the scale, I make sure to set it to zero first.

I want a consistency of 67, which is 2 to 3 parts by weight,  of water to plaster. I am using 0.5 pounds as one part. So three parts of plaster weighs 1.5 pounds.

I pour clean fresh water from the yogurt container into another clean mixing bowl until it weighs 1.0 pound.

Always add plaster to water.

I use the scoop to rapidly sprinkle the sifted plaster into the water. I try to sprinkle the plaster as evenly as I can. After all the plaster has been added to the water, I let the plaster slack for awhile, until all the dry plaster has soaked up water. In the snapshot below, the plaster is slacking.

After slacking, I push the island of plaster to the bottom of the mixing bowl with my fingers, and I mix the plaster and water until it is smooth and creamy. It is ready to pour when I can trace an S in the plaster, and see it afterwards.

I turn ON the vibrator.

I pour the plaster in an even stream into the prepared coddles until it rises to the height I want it to be, which in this case, is to the top of the ribbon of clay that defines the shape of the foot. Then I turn OFF the vibrator.

The excess plaster is put into the trash container.

I wash the mixing bowl, any tools that have wet plaster on them, and my hands in the bucket of water.

NEVER put plaster (dry, set, or wet) down the drain pipes.

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