You should only do this when the wallboard/drywall is "blueboard" (has a blue colored paper on it). It has the necessary treatments to repel the water in plaster. If you don't have blueboard up, you can use common drywall joint compound to simulate the look of plaster if you wanted. You might mix in a small bit of plaster into the compound to help give it some durability, but only mix small batches or it will dry before you can make use of it.
You should only do this when the wallboard/drywall is "blueboard" (has a blue colored paper on it). It has the necessary treatments to repel the water in plaster. If you don't have blueboard up, you can use common drywall joint compound to simulate the look of plaster if you wanted. You might mix in a small bit of plaster into the compound to help give it some durability, but only mix small batches or it will dry before you can make use of it.