Types of Molds
There are two types of alginate molds- a "Bucket Mold" and a "Layup Mold".
In a Bucket Mold, the alginate is poured into some type of container and the mold is made in that. Plaster bandages are not used in Bucket Molds.
In a Layup Mold, the alginate is applied to a surface (like the face or torso). Since the alginate is applied only about 1/4 inch thick, it needs to be reinforced so it doesn't flop around like a deflated balloon when the mold is removed.
Types of Plaster Bandages
The ONLY kind of plaster bandages we're interested in for LifeCasting are the "Extra Fast Setting" ones. These will reach 90% of their final strength within about 5 minutes. If you get longer setting bandages, you will be sitting around a long time in the studio with a fairly upset model. Don't do it.
Sizes of Plaster Bandages
Plaster Bandages typically come in rolls that are 5 yards (15 feet) long. They come in a variety of widths, including 3-inch, 4-inch, 6-inch, 8-inch and 12-inch widths. The most popular are 3- and 4-inch ones. If you are planning a really big job like a full torso or more, you should consider 6- or 8-inch bandages to reduce the amount of time spent applying them.
How to get PBs to Stick to Alginate
When you remove a layup mold from the model, you want the plaster bandage shell and the alginate to come off as one piece. If they separate, it can be very tricky to line them back up together prior to pouring and your results can be compromised.
Various techniques have been developed. All of them depend on embedding something IN the surface of the alginate before it sets. In layup molds, the alginate will set first against the skin- warmer- and last on its outside surface. We take advantage of this phenomenon to accomplish our goal.
Just as you are finishing up the alginate application you will notice that the alginate on your hands starts feeling different. This it beginning to set against your skin. It will still be quite sticky on the outside surface for a while.
One technique is to embed small pieces of dry plaster bandage (1 inch x 3 inch) IN the surface of the alginate- especially around the outside perimeter. This is the technique we recommend in our face, head and torso casting kits.
Another technique uses a sheet of that white polyester stuffing used in inexpensive quilts. It is available at yardage stores everywhere. The sheet is pushed up against the alginate surface where the tiny fibers get stuck in the setting alginate. When the alginate is fully set, peel off the sheet of polyester and many, many of those fibers will remain behind bristling from the surface of the alginate.
In either case, we have given the plaster bandages we will be applying for our shell something to stick to. If done properly.
How to Keep PBs from Sticking to your Model
Plaster can be nasty. If it comes in direct contact with unprotected skin, it will completely encapsulate each and every hair it touches. When the plaster is removed, it will yank them all out- another way to get your model to have unkind things to say about your- probably to your face.
The only reliable way to keep plaster bandages from sticking is to put a thin layer of petroleum jelly or baby oil on the skin wherever the bandages might touch. This coats each of the hairs so the plaster can't stick to them as well. We took a vote and 97% of all models preferred this technique.
How many Plaster Bandages?
The age old question. The answer is- It depends.
Small layup molds like face molds aren't very heavy even after being poured. They don't require very many layers of PBs- maybe 3-4 layers. A couple of rolls of 3x5yd bandages will be sufficient.
Large layup molds like full torsos are heavy and awkward all by themselves and get VERY heavy when poured with LiquiStone. These need to be very strong if you don't want them to bend, twist or fold up when removing them and when pouring them We recommend 8 full layers of bandages for these. This is a lot of bandages- at least a case of 12 4x5yd bandages.
Wetting Plaster Bandages
A flat, wide container is ideal for wetting plaster bandages. Cool water is best. Dunk the bandage into the water for a couple of seconds. Gather it up into a ball and squeeze gently to remove the excess water. Do NOT squeeze too tightly or you will squeeze out much of the plaster as well. Overwetting and oversqueezing are the two main potential problems.
Applying Plaster Bandages
Two things to keep in mind.
DO make the outside edge of your plaster bandage shell one or two layers thicker than the rest. The extra rigidity of the perimeter will help keep the mold from twisting or bending during pour-up. Less distortion and better results.
DO NOT stretch the plaster bandages tightly when applying. If you stretch the plaster bandage you are actually pushing downward on anything that is sticking UP in the mold. A nose is perfect example. This can deform the mold. Apply the plaster bandages on loosely and rub them down into the low spots gently.
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