The only drawback is that even after curing it stays soft and flexible. Therefore, it has to be reinforced with a mother mold that will enable it to hold its shape. Plaster bandages are commonly used for this purpose. Thin strips of plaster are rolled out, wetted and applied over the alginate. The plaster in the bandage dries quickly to form a firm and supportive shell mold.
However, the plaster itself may tend to peel back or curl away at times, especially on large surfaces. This will disengage the alginate and can distort the shape of the body mold.
We can overcome this problem by making locking keys before applying the plaster bandages. Place small acorns or clay molds with undercuts around the alginate mold while it is still mushy. Ensure that you completely cover these protrusions with plaster bandages as you work your way over the alginate. These ‘keys’ will lock the alginate and plaster molds together to form a hard body mold.
The plaster sets quickly and is demolded from the model before beginning the life casting process.
Keep in mind that at no point do you have to ‘unlock’ the two molds. They are used together during the casting.
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