Things You'll Need
Fiberglass is a great material to make objects with, but as fiberglass cloth is soft until painted with resin, it is difficult to use without a mold. You can easily make a mold with air-dry clay by hand. This will allow you to take your time to produce the perfect mold before setting the fiberglass on it. Air-dry clay is cheap and readily available, and it does not require firing in an oven, making it an ideal substance with which to build molds.
Remove the air-dry clay from its packaging and wet your hands with some water. Knead the clay with your hands to warm and soften it.
Shape the clay using your hands into the shape you would like to mold your fiberglass. Remember that when making a mold, you will need to create an opposite surface from the object you would like to produce with fiberglass.
Use a ruler or knife to smooth surfaces and create straight edges where needed. Wet the clay with a small amount of water whenever it becomes hard or difficult to work with, or when requiring the joining of two separate pieces.
Set the clay aside when the desired shape has been made. Allow 24 hours for it to dry and harden before attempting to apply the fiberglass.
Coat with a thin layer of vegetable oil prior to the application of fiberglass cloth and resin to allow the fiberglass to be easily removed from the mold once it has cured.
It is much easier to mold clay than to shape hardened fiberglass. Take the time to make a perfect mold so you will not have to make alterations afterward.