Friday, July 18, 2014

09 Plaster Production Molds Nº 81

Oops !. This mixing bowl is much too small. Click on the image to enlarge it.

Some Arithmetic

I measured the inside dimensions of the mold, and it is 4.75 inches wide by 8.75 inches long by 3.375 inches high, more or less. That comes out to about 140.27343 cubic inches of volume. This is a very rough estimate. There are 14.4375 cuin in 1 US cup. So 140.27343 cuin divided by 14.4375 is 9.71590 cups.

Now, there are 8 ounces in one cup, so 8 oz X 9.71590 cups is 77.72720 total ounces of water. And 77.72720 oz divided by 16 oz of water in one pound comes out to 4.85795 pounds of water.

How many ounces is .85795? 16 oz times .85795 is 13.72720 oz, which can be rounded off to 14 ounces. So the water will weigh about 4 pounds 14 oz.

I want a mold consistency of 67 (which is 2 parts of water to 3 parts of plaster, by weight). So 4 pounds 14 ounces divided by 2 will give me ONE part, or 2 pounds 7 ounces.

To get the total weight of plaster, I multiply 2 pounds 7 ounces X 3 to get 7 pounds 5 ounces of plaster.

So when I find a larger mixing bowl, I will weigh out:

4 pounds 14 ounces of water (just under 5 pounds), and
7 pounds 5 ounces of plaster

That should give me a little bit more plaster than what I need. Better to mix a little bit more than not enough.

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