How much alginate do I need?
This is usually the first question we get asked- just before "What kind of alginate should I use?".
As you may know, there are two basic types of alginate molds- The "Bucket Mold" (hands, etc.) and the "Layup Mold" (faces, torsos, etc.).
The Short Answer
|Baby Hand Casting
||~ 3 ounces
|Child Hand Casting
||~ 6 ounces
|Adult Hand Casting
||~ 1 pound
|Adult Double Hand
||~ 1.5 pounds
~ 4 ounces
||~ 1-2 pounds
|Half Torso Front
||~ 0.75 pounds
|Full Torso Front
||~ 1.5 pounds
For a more detailed answer, read on.
The Bucket Mold
In a Bucket Mold, alginate is mixed and placed into a container (bucket). The body part (a hand is a perfect example) is pushed down into the alginate to make the mold. The bucket holds the alginate and keeps it in place.
In a Bucket Mold, the alginate fills the space between the hand and the inside of the bucket so the smaller the bucket, the less alginate you will require. The bucket must be big enough so the body part doesn't touch the inside or the bottom, but not overly large. (Just imagine how much alginate you'd need if you did a hand casting in a bathtub.)
The easiest way to calculate your alginate requirement is:
- Fill the bucket with water
- Put the body part in- allowing the excess water to flow out
- Measure the remaining water
- Since a pint of water weighs almost exactly 1 pound, for every pint (16 fl.oz) water you have left over, use 1/4 pound of alginate. That's our 4:1 ratio
Remember, we recommend our 270-D, 370-SD, 380-CC, 390-S2 and 570-PGV alginates for bucket molds. Bigger jobs generally require more working time.
The Layup Mold
In layup mold, the alginate is applied directly to the skin. Common examples of layup molds are face casting and torso casting. Layup mold alginate requirements are based on square inches of area to be covered by the alginate. Since alginate is usually applied about 1/4 inch thick, some simple calculations should give you what you need.
We have found that 1 pound of alginate mixed 4:1 (water to powder by weight) has a total volume of approximately 137 cubic inches. Mixed at 3.75:1 (our "thick mix") that figure drops to about 128 cubic inches per pound.
Now, since we are only applying the alginate 1/4 inch thick, we multiply those figures by 4 and get an approximate surface area coverage, per pound, of:
- 548 square inches at 4:1
- 512 square inches at 3.75:1
An approximate measurement of the area to be covered can be done by measuring the height and width of the area (in inches) and multiplying them together.
For example, my full torso is approximately 24 inches tall by 18 inches wide, or 432 square inches.
This area could easily be done with just one pound of alginate. Always mix a little extra because it is MUCH better to have a little bit too much than not quite enough.
A face is generally a circle about 12 inches across. That give us a figure of 113 square inches, so a face can easily be done with just 1/4 pound of alginate (actually 3 ounces is generally enough).
If you still have questions, please feel free to contact us. We'd be happy to discuss your project with you.