Do you mean plaster gause/ bandages ( the stuff that comes in a roll and you just get wet to use it ) ?
You are planning on making armor from this?
That stuff is good and strong when it dries , which is why it is good for making mother molds on top of less sturdy molds, but making armor out of it?
For one thing it is gonna weigh a ton. second it probably isnt going to be the easiest thing to shape. and third, unless you seal it good it will deteriorate back to dust almost once all the water eveaporates it will become brittle.
If you just want to shape it with your hands i would use modeling clay and then make molds from those, that you can make duplicates of your armor in different materials. The one draw back to this method is that it can get expensive.
Another option is to just carve your pasrt out of plaster block and then vacume form plastic on top of those pieces. you can make a cheap vacume forming table if you have a good shop vac and some tools.