Welcome Back to Creating a Baby Belly Mold Step Four: Now comes the fun part. You want to have a couple of bowls of water handy. Change the water if it starts to get "creamy". Instructions for the plaster depends on the kind you buy but they are all are pretty close. Fill the bowls up with water, tempeture should be around 22-25 degres celcis. Take the bandges and immerse them into the water for 3-5 seconds. When you take the bandgage out hold the 2 ends up in the air close to each.