Linda Blossom on tue 20 apr 99
It always drove me nuts that plaster was always expressed in parts of water
to parts plaster but there was never a way to figure out how much of what
was needed for whatever volume I was casting. I found something close to
that in John Kenny's book. He said that one quart of water plus 2.75 pounds
of plaster would make an 81 cu inch, or 9"x9"x1" bat. So I was using that
by measuring l x w x h and dividing the resulting cubic inches by 81. When
I did a shape that could not be measured such as a bowl shape I would use
quarts of water to figure out the volume. However, I always made too much.
After a while I figured out that I was using the total plaster/water volume
when measuring when I should have been getting the amount of water only
volume needed then adding the appropriate amount of plaster to the water.
I figured out how much water was needed for an 81 cubic inch volume
container. It turned out to be 61 cubic inches of water (which is 75% of
81.) The procedure for a rectangular container is: measure the length by
the width by the height then divide this number, which is the cubic inches,
by 81 and then take the result by .75 which is the percentage of water to
water/plaster volume. This is the amount of water needed. Then multiply
this number by 2.75 to get the plaster. To do this with a bowl or other
round container, measure with quarts of water. Multiply the number of
quarts by .75 and then multiply by 2.75 to get the pounds of plaster. If I
am casting something that is large, I estimate how many cubic inches I think
it takes up and deduct that from the cubic inch measurement.
Now I realize that there is probably a more efficient way to do this but
being very inefficient with math, this is what I came up with.
Linda Blossom
2366 Slaterville Rd
Ithaca, NY 14850
607-539-7912
blossom@twcny.rr.com
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